# Panel Saw Tensioning



## Rhyolith (19 Feb 2016)

I friend wants to know how to re-tesion panel saws (if they get bent or other wise damaged). 

Does anyone know how this is done?


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## Cheshirechappie (19 Feb 2016)

I know of four methods.

Method 1 works for definite kinks on some (not all) saws. Place the sawblade with the peak of the kink against the bench edge, and using the thumbs either side of the kink, bend it out. This can take quite a lot of force, but it's best to start gentle and work up the force scale. I've had success with this method on one saw with a kink resulting from jamming in the cut.

Method 2 is one I've not tried, but is said to work for blades with an even curve in them. First, submerge the blade in boiling water, or pour boiling water over the blade. Then, wearing thick gloves, flex the blade against the curve until the blade comes straight. Allow to cool, check, and repeat if necessary.

Method 3 works for blades with multiple kinks. Using a heavy hammer with a clean, preferably polished, face (any marks on the hammer face will transfer to the blade), place the blade on an anvil concave side of each kink down, hold it tight to the anvil, and using heavy, dead blows, knock the kinks out. Again, start gentle and work up the force scale - too heavy a blow could result in cracking, and there isn't a huge margin between yield point and ultimate strength of the material - not much plastic deformation is possible. I've had some success with this method, but it takes a bit of practice to get a blade really straight.

Method 4 works for blades with slight bulges and gentle bends. Using a hammer with a straight (or cross) pein and a block of hardwood, place the blade concave side down, and tap the hammer such that the pein makes a line of blows across the bend. The idea is to use the give in the hardwood to induce a very slight bend in the blade opposite to the bend to be removed. Continue with lines of blows across the bend until it is eliminated. I've not tried this one, but it should be a little easier than the anvil method. Again, some practice with weight of blow would be required.

There was (is?) another, used to remove bulges. The metal either side of the bulge was hammered to stretch it - note, NOT the bulge itself. I've not tried that one, and I suspect it's a rare fault in saws that have seen service, but would be common during the manufacturing process after heat treatment of the blade.

The key to all of these is careful assessment of exactly where the bends and kinks are. The professionals used to hang the saw up such that the blade hung vertically, and use two wooden straightedges one each side of the blade to find the faults.

Hope that helps a bit!


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## biskit (19 Feb 2016)

(hammer) (hammer) (hammer)


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## D_W (19 Feb 2016)

Rhyolith":t1zlfxnb said:


> I friend wants to know how to re-tesion panel saws (if they get bent or other wise damaged).
> 
> Does anyone know how this is done?



Hammer lightly and evenly on both sides of the saw. Inevitably, the saw won't be straight when doing this, but additional strikes on one side or the other (depends on what's under the saw) will bring the tensioned saw back to straight.

Presume every saw you find (other than japanese saws) will have been tensioned on rollers (if it was, in fact, tensioned).


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## Rhyolith (20 Feb 2016)

Thank you Ches. 

I know of the first method, but never heard of the boiling water one before! It seems to me that Methods 3 & 4 require a fair bit of practice to get right, its a another reason to buy old cheap saws to practice on (which i want to do to practice saw sharpening as well). I usaully just cut of the end of bent saws (which leaves me with rather useful stubby panel saws), but it will be good to have a few alternatives. 

My friend thinks there is some kind of "trade secret" to re-tensioning the blade of panel saws (Dissitons usually the subject of the conversation), by re-tensioning I think he means stifferning the saw along its back by stressing the metal to strench the cutting part out (imagine like a coping saw). Apparently a similar thing is done with circular saws, but I have no expierence of that. 

I am talking about the old Dissiton Panel saws here mostly, as it is those me and my friend would like to restore.


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## CStanford (20 Feb 2016)

http://www.wkfinetools.com/tRestore/saw ... Blade1.asp


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## Cheshirechappie (20 Feb 2016)

Rhyolith":2jj0uc3b said:


> My friend thinks there is some kind of "trade secret" to re-tensioning the blade of panel saws (Dissitons usually the subject of the conversation), by re-tensioning I think he means stifferning the saw along its back by stressing the metal to strench the cutting part out (imagine like a coping saw). Apparently a similar thing is done with circular saws, but I have no expierence of that.



There's been much discussion about 'tension' in handsaws, but I've never seen anything that explains what it is, how it works, or even convinces me that it exists at all. Most of the references seem to suggest that a 'tensioned' handsaw is stiffer than one that has not been 'tensioned', but I don't see how hammering a piece of sheet metal of a given thickness and hardness can make it stiffer.

The reason saws were hammered years ago was to correct distortion that occurred during heat treatment - the process by which soft steel was given more hardness and the springiness needed to avoid their being easily bent or kinked in use. Modern heat treatment methods allow the production of flat steel sheet hardened and tempered to spring grade - and crucially, still flat.

If a piece of soft sheet iron or sheet steel is hammered evenly all over, it will work harden, and go from a state in which it bends or kinks easily to a state in which it will hold it's shape better. Maybe that's the origin of the misconception - back in the 18th and early 19th century, the cheapest grades of saw were made from sheet iron hammered to give them some spring. At least one contemporary writer (Moxon?) advised against purchasing such saws, and stated that the steel ones were much better.

Circular saws are different animals altogether. When spun at full cutting speed, a fair bit of tensile stress develops in the periphery of the saw. (Same thing happens to anything spun - the old cast iron flywheels of mill engines have been known to 'burst' if the engine oversped because the tensile stress in the rim exceeded the cast iron's ultimate tensile stress - with very distressing consequences to anybody in the vicinity.) With a circular saw, the tensile stress developed produces an associated strain. In simple English, the rim stretches. The metal nearer the centre of the saw doesn't stretch as much because the stress isn't as high near the middle, so the only thing the rim can do to relieve the strain is to distort into a sideways wave. The saw thus won't cut straight.

To cure this problem, circular saws, especially large ones, used to be made like very flat cones. As the saw reached working speed, the periphery stretched, pulling the cone flat. Modern saws have small cuts around the periphery that effectively divide the toothed edge into segments, and give a little space into which the metal at the periphery can expand at working stress (thus allowing circular saws to be made from flat stock).

A handsaw does not see such stresses. Indeed, the forces acting on a handsaw cutting edge are very low, especially when the saw is sharp and in good condition - a fact readily proved by the lack of effort required to use a good saw. Using a saw with any force risks a jam and a kinked blade.

It sometimes happens when using a panel, hand or rip saw that the toe end waggles about as the saw is returned for the next cutting stroke. I've had this happen when using a saw horse of less than ideal height - a Workmate, for example. It happens because the body position is not good, and the sawing arm isn't keeping a straight line, so the saw is being pulled just a bit sideways, causing the teeth to rattle against one side of the cut. With a better sawing position that keeps the sawing arm straight with the cut, it doesn't happen so much. I've seen people say that to eliminate saw toe-end waggle, they need a saw with more tension. Wrong - they just need a better sawing position.

If someone can explain what 'tension' is in a handsaw, and how it's produced, and demonstrate the fact, I'll listen. However, until I've seen someone make a saw noticeably stiffer by hammering it, I remain unconvinced that 'tension' in handsaw blades actually means anything other than 'straight'.


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## AndyT (20 Feb 2016)

I'm away from my books at the moment so can't look it up, but somewhere I recall a diagram in an old book purporting to explain this tension.

It likened the saw plate to a piece of paper hung up by its top edge, with the teeth along that edge. To have any chance of cutting, the fingers holding the paper need to stretch that edge so it goes taut. This is achieved, so the book said, by hammering the metal behind the edge so it is trying to be longer than the edge, with the result that the edge goes stiff.

I'll try to find the source when I can, or maybe someone else will recognise it.

It could be a load of old tosh, though!

(It might have been in a book on tools for woodwork by JC Brough, which I was looking at having watched a recent video review of it by Graham Haydon, but I'm not sure.)


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## Cheshirechappie (20 Feb 2016)

Indeed, Andy - I'm fairly sure I've read similar here and there, and the authors may well have sincerely believed what they wrote. However, I think it is a load of old tosh.

Firstly, sawblades are substantially thicker (and inherently stiffer) than sheets of paper. Secondly, if part of a sheet of steel is stretched and part not, the shape of that piece of steel must change to accommodate the stretched part. The fact that saw blades stay flat indicates that the strip behind the toothline hasn't stretched at all - the blade would bow if it had.

The hammering process during manufacture is undertaken to change the blade's shape by removing bends, kinks and bulges and make the blade as flat and straight as the smith can manage. Any hammering sufficient to stretch part of a blade that already IS flat must therefore, by extension, remove the flatness created - exactly what is not wanted!

Edit to add - the only way I can think of to make a sawblade stiffer (other than to make it a backsaw) is to make it from thicker material to start with. Stiffness of flat pieces of material is proportional to the cube of their thickness, so not much thicker makes it significantly stiffer. Conversely, not much thinner makes it significantly more flexible.


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## Rhyolith (20 Feb 2016)

AndyT":e4a83mrq said:


> It likened the saw plate to a piece of paper hung up by its top edge, with the teeth along that edge. To have any chance of cutting, the fingers holding the paper need to stretch that edge so it goes taut. This is achieved, so the book said, by hammering the metal behind the edge so it is trying to be longer than the edge, with the result that the edge goes stiff.


Thats exactly what I was trying to state earlier. As thinking about it, it's the only logical way I could think of to make the blade mechanically stiffer... short of some metallurgical magic I don't understand yet  I can see it being difficult to achieve (maybe impossible) to tension the blade in this way without cause it to go all over the place (bend), but maybe if the central portion of the blade (the strip between the back and the cutting edge) were not tensioned and the back was this would keep it straight? I am imagining it working like a hacksaw with is sprung back and tort blade, just in one sheet of steel... mechanically I don't see why I would not work.


CStanford":e4a83mrq said:


> http://www.wkfinetools.com/tRestore/saw/strSawBlade/strSawBlade1.asp


This seems to treat saw tensioning as a real thing, but I have only read the 1st page so far (slow reader). Thanks for the link Stanford, its more or less exactly what I was after  I am very interested to find out whether saw tensioning is myth or reality now though.

Yes, please find that reference when you can Andy. Info on saws is remarkably hard to come by.

Edit: I had a thought, if a panel saw is really tensioned like a hacksaw, then cutting into the the cutting edge of the blade to about half way through (give or take) should cause it to bend upwards of its own accord... If any has a old panel saw they don't mind ruining :?


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## blackrodd (20 Feb 2016)

When I worked in the saw shop, I was not taught the art of Rolling, hammering or tensioning but did watch when possible, probably when I should have been sharpening.
I have found a link below, which helps show when tension is lost, nearly always by overheating.
The handsaw "flapping" is mainly caused by not allowing the saw to dominate the cut, but trying to speed up the saw, easily done when sawing with both hands, and "slogging" away, the timber closing on the blade, 
waxing the blade helped cure this.
In the days before laser welding made cheap TCT blades available, An Untensioned mild steel circular saw blade would not stand the rigours of spinning and sawing in a straight line.
It's heat treated as hard as possible, yet allowing the sharpening by file.
In the mill when the new blade was fitted, the blade was packed each side using the correct wadding and the ever present fag packet unfolded and used.
The fibre packing was about 4 " long and started just after the gullet, and sit in a rebate, about 5/8 deep, but flush just under the bed height.
When too tight the blade would wobble quite soon after start up.
Too slack and the blade would tend to "meander"in the cut, particularly around knots in harder wood.
It was all too easy to burn the saw, when pinching and kickback occurred, sometimes you could get halfway down a
8' or 10' board before trouble ensued.
Then the saw doctor was not a happy bunny, brown and blue hot spots on the blade, had to be hammered and re tensioned, and then the "hotspots"polished with emery tape to hopefully ensure the burn wouldn't catch again.
Regards Rodders 

https://www.youtube.com/watch?v=6rLmeZ8CGBQ


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## Cheshirechappie (21 Feb 2016)

Thanks for that link, Blackrodd - it must be one of very few indeed on the subject of circular saw doctoring!

As I said in my first essay, circular saws and handsaws are very different animals. Circular saws see stresses at working speed that no handsaw will ever see, and have to be set up to cope with those stresses. If you look very carefully at the video, you can see what he's doing - making the saw into the very flat cone I was talking about. When he puts the longer straightedge across the saw, it touches at the periphery, but there's a small gap nearer the centre. You do have to know what you're looking for when you watch, and if you blink you'll miss it - but it's there.


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## CStanford (21 Feb 2016)

Here's a section of an article on the Disstonian Institute web page.

"The next step is that of "Smithing." in this the blades are flattened and made perfectly straight, all inequalities being taken out by the skillful hammering of the mechanics. 

The blades are next "Ground" to gauge and to a taper so that the back will be thinner than the cutting edge. The back of the hand saw blade is ground to taper from the teeth to the back and from handle to point, the tooth-edge being of even thickness from end to end. A saw not ground to proper taper cannot be ranked as a high-class tool. 

After being ground they are returned to the smithers for "Looking-over" and preparing for next operation. 

*Now follows "Tensioning." *In this the blades are hammered so that they shall not be too "fast" or too "loose;'' but shall possess the proper tension, spring or character. If the blade is what is termed "fast" the metal is too long on the edge and needs expanding through the centre, or, if too "loose" the metal must be stretched on the edge. A saw not properly tensioned will run out of its course, in other words it will not cut straight and true. "

Another link that might be helpful: http://www.wkfinetools.com/mLibrary/Gri ... Filing.asp


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## Cheshirechappie (21 Feb 2016)

CStanford":f2q42azb said:


> *Now follows "Tensioning." *In this the blades are hammered so that they shall not be too "fast" or too "loose;'' but shall possess the proper tension, spring or character. If the blade is what is termed "fast" the metal is too long on the edge and needs expanding through the centre, or, if too "loose" the metal must be stretched on the edge. A saw not properly tensioned will run out of its course, in other words it will not cut straight and true. "



That just means 'flat and straight', doesn't it?

I've seen the terms 'fast' and 'loose' (sometimes 'tight' and 'loose') used in other references, where it means slight humps and bulges. A slight bulge is 'loose', and the metal either side of it is 'tight'. All it means is the correction of any out-of-flatness found after grinding. Just as plane sole castings can distort after machining if they're not annealed or seasoned, steels - especially thin, flat plates - can distort if ground after heat treatment, especially if the heat treatment was of the 'old school' type done in coke hearths without the benefits of modern controls. Slight differences in temperature across a plate when it was quenched would give slight variations in hardness and temper, hence slight stresses set up in the quenched plate, hence the distortion as those stresses are partly released by grinding or surface finishing.

Modern saws made from spring steel of even hardness and temper throughout, supplied by the mill in a flat, smooth condition, just doesn't need the corrective smithing, because it stays flat. A saw bent in service just needs enough hammering to bring it straight enough for service again.

Thanks for the link to 'Grimshaw on Saws'. I bought a copy of that from Abebooks (their 'print on demand' service for old books - doubt I'd find or could afford an original!). There's nothing in it that suggests to me that handsaw hammering was anything other than a way to get them flat and straight.


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## CStanford (21 Feb 2016)

"...but shall possess the proper tension, spring or character..." Seems to indicate something other than just the removal of bulges or making the plate flat.

Could be that modern saw stock is 'better' but the saws don't really seem to be any better (not all that worse, either, I'll grant). Maybe they're better in the sense they're more easily made entirely with machines.


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## Cheshirechappie (21 Feb 2016)

CStanford":3dmewahv said:


> "...but shall possess the proper tension, spring or character..." Seems to indicate something other than just the removal of bulges or making the plate flat.



Not sure about that. A sawblade is basically a piece of flat spring steel with teeth along one edge. You'd want it to have 'proper tension, spring or character' - in other words, springy, or elastic; having the capacity to return to straight if deflected. The springiness is imparted by the hardening and tempering, the subsequent hammering corrects any distortions arising. Thus, when finished, the sawblade is flat, straight and springy.


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## CStanford (21 Feb 2016)

Bad Axe Tool Works mention the word 'tension' in their entry regarding straightening saw plate:

"The reason so many saws (particularly back saws) have a chip in the handle or a missing horn is because a previous owner dropped it; this most likely put a kink or bow in the sawplate, because the rib of metal (back, or spine) of the saw no longer exerts even pressure across the length of the blade. Acts of careless sawing also result in bows and kinks in the sawplate. Consequently, many old saws present a taper from toe to heel, because to straighten a bow after dropping the saw (and chipping the handle), a previous owner tapped the spine at the toe deeper into the sawplate—an inelegant correction at best. I can remove the back, judiciously hammer the kink out on my saw anvil, replace the back, equalize blade depth the way Disston (and other manufacturers) originally made the saw, and deliver a restored blade to you that cuts faster with a thinner kerf. Same technique applies for handsaws, obviously without the back. Do understand that hammering a sawplate straight often results in a 90% solution. Once badly kinked, a sawplate will always be weaker in that spot, and overhammering will result in a permanent loss of tension. Sometimes, there is a point where you just have to accept less than perfection. For sawplates with a significant buildup of rust, add another $20."

It apparently applies to circular saw blades as well. http://www.carbideprocessors.com/pages/ ... plate.html

"As a final step the plate is examined with a flat edge and hand hammered to correct high and low spots as well as to ensure proper tension in the steel. 

A circular saw must be tensioned to operate properly; the larger the saw is, the more important it is to have the proper tension. As the saw comes up to speed, the rim stretches much more than the center of the saw, due to centrifugal force. 

An untensioned saw will be loose and floppy at speed and will wander out of the cut and heat up."


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## Cheshirechappie (21 Feb 2016)

That's Mark saying he can't always get them dead flat, which is perfectly understandable. He flattens maybe one or two a week; the old saw smiths of Sheffield and Disston were doing them 50 hours a week 50 weeks of the year. Also, too much hammering on a bad kink can crack the blade - there's not a huge margin between elastic limit (or perhaps more accurately, something like the proof stress point) and ultimate tensile strength in hardened steels - not much plastic deformation is possible.

We covered circular saws earlier in the thread.


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## CStanford (21 Feb 2016)

I didn't realize that the word tension was synonymous with a flat or out-of-flat condition; one can apparently take their pick. :roll:

I always thought the word 'flat' did a nice job of describing the condition of flatness. And 'not flat,' the converse.

The fact that sheet steel stretches, well all steel stretches just ask a bridge engineer, seems to indicate the presence of tension somewhere in it.

The phrase tensile strength has some meaning in physics.


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## CStanford (21 Feb 2016)

I'm going to post this link one more time in hopes that somebody won't go willy-nilly whacking a kinked saw with a hammer and expect good results. You won't get them. Of this, I'm sure. Otherwise, bowing out of the thread.

http://woodcentral.com/articles/handtoo ... _866.shtml


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## D_W (21 Feb 2016)

Am I getting it correct here that some of the posters think there is nothing happening to a blade that's tensioned other than to straighten it?

All one has to do to confirm the effect of tensioning is use a lower grade saw that is not properly tensioned. Saws were rolled to make them stiffer, not straighter.


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## worn thumbs (21 Feb 2016)

Bob Smalser covers the topic well.The topic reminds me of a presentation I saw back in the eighties from a company specialising in shot peening and focusing on the benefits of imposing a force on the surface of the material by impacting it with a lot of small blows.It seems to me that the principle is very similar and like Mr Smalser,I would suggest anybody keen to learn more should seek out a cheap,distorted saw to help them understand the process.


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## Cheshirechappie (21 Feb 2016)

D_W":35qdekx1 said:


> Am I getting it correct here that some of the posters think there is nothing happening to a blade that's tensioned other than to straighten it?
> 
> All one has to do to confirm the effect of tensioning is use a lower grade saw that is not properly tensioned. Saws were rolled to make them stiffer, not straighter.



You are correct in assuming that some of us (well, me anyway) are not wholly convinced. I've read a great deal about it, and seen the word 'tension' bandied about in several rather imprecise ways, but I have yet to see anything that convinces me that taking a flat, straight, properly heat-treated sawblade and hammering it will in some way make it stiffer or springier. 

Something that would sway my opinion is somebody making two identical saws - same grade of steel, same thickness, same size - and 'tensioning' one of them, them demonstrating a difference in performance between the 'tensioned' and the 'untensioned'. Until we can all see a clear difference between the two, it does seem that there is a bit of, "I read it somewhere therefore it must be true" going on. Can those who assert that hammering or rolling a sawblade makes it stiffer or springier prove their assertion?

As far as comparing a lower grade of saw with a higher grade of saw - well, I'm not trying to be rude, but what would you expect?


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## Cheshirechappie (21 Feb 2016)

worn thumbs":18xvxhec said:


> Bob Smalser covers the topic well.The topic reminds me of a presentation I saw back in the eighties from a company specialising in shot peening and focusing on the benefits of imposing a force on the surface of the material by impacting it with a lot of small blows.It seems to me that the principle is very similar and like Mr Smalser,I would suggest anybody keen to learn more should seek out a cheap,distorted saw to help them understand the process.



Shot-peening is a process used for stress relieving (or for heavy cleaning). Needle-gunning has a similar effect. The effect tends to be confined to the surface layers, and is not as effective on thick pieces as heat treatment. However, when heat treatment isn't possible, it can help a bit.


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## Cheshirechappie (21 Feb 2016)

CStanford":31xq8aap said:


> I didn't realize that the word tension was synonymous with a flat or out-of-flat condition; one can apparently take their pick. :roll:
> 
> I always thought the word 'flat' did a nice job of describing the condition of flatness. And 'not flat,' the converse.
> 
> ...



Charles - by profession, I'm a mechanical engineer, so I'm familiar with the precise 'physics' meaning of the word tension. That's what leads me to question a lot of the old writings. 

If you take a piece of flat steel, and stretch part of it, it won't be flat any more. Either that, or part of it will be thinner - you cant increase a material's dimension in one plane without reducing it in at least one other. If part of it is thinner, it's less stiff, not more.


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## CStanford (21 Feb 2016)

I think you just described tensioning a saw.


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## Cheshirechappie (21 Feb 2016)

Charles - if it's thinner, it's LESS stiff. Not more. And if it's bent, it's not much use as a sawblade.


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## D_W (22 Feb 2016)

I'm comparing nearly identical old rip saws. One floppy and with no makers mark, and the other a disston 7.

Both have the same hardness under file. It's something you have to observe by feel. Reading about it will not illuminate anything.


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## Cheshirechappie (22 Feb 2016)

D_W":cppo6tck said:


> I'm comparing nearly identical old rip saws. One floppy and with no makers mark, and the other a disston 7.
> 
> Both have the same hardness under file. It's something you have to observe by feel. Reading about it will not illuminate anything.



A few questions, if I may.

1. From what grade of steel is each saw made?

2. What are the dimensions of each saw, including thicknesses (at the toothline, and at points across the blade to the back.) Putting it another way, are both blades identical in size, shape, thickness and taper grinding?

3. What manufacturing processes did each saw undergo, and to what degree of hardness and temper is each blade made?

Once we know that, we know what we're comparing.


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## D_W (22 Feb 2016)

The saws were identical in size - 26 inch 5.5-6 point rip saws that are about 40 thousandths at the tooth line mid/back, and maybe slightly thinner at the to. Similar thickness at the top of the taper. 

One saw was a disston 7, the other generic with no mark and a warranted superior medallion (but it was old enough to have a nib). 

One never knows what steel was in them, it's a mistake to apply a "is it 1080 or 1095?" kind of thought to it. Most older saws were probably about 8 tents of a percent carbon, and hardened somewhere in the high 40s hardness range. You get the sense of the plate hardness by filing the teeth - both saws were new enough that the hardness was even toe to heel. 

Just as another aside, every time I get an atkins crosscut saw, they are floppy compared to a disston. I would assume it's because of their tensioning process, because there is again, no difference under the file (and I think rob streeper on another forum actually struck these saws to confirm they're about the same hardness). Whatever it is that atkins did, it makes it so that if you want to convert a 7 or 8 point crosscut saw to rip for hardwoods or for resawing really hard woods, the saws don't have the stiffness to do the job without too much (in my opinion) care from the operator. 

I suppose I have yet one more, a "tip top" marked rip saw that's actually a bit thicker than a comparable disston, but still floppier. Same with an old bakewell rip saw. 

What you're lacking here isn't reading, it's getting out and filing and picking up some saws. You're not going to come to a reliable conclusion. 

On a handsaw, the tension is in the surface. If you wanted to do an experiment for yourself, you could get a small but good quality panel saw (like an old disston 12 22-24 inch sized saw) and get a good stiff disston rip saw like a D8, and grind (by hand sanding) the D8 until it was similar thickness to the panel saw - about a hundreth less. If you did that by grinding off both sides, you'd be left with a floppy saw with no tension. 

I haven't used a modern 1095 hand saw, but I have some doubts that they're as stiff as a good 1900 D8, even though you will have a whole lot of trouble finding someone who grinds as much off as disston did in tapering.


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## Cheshirechappie (22 Feb 2016)

It occurs to me that the word 'tension' has been used a lot in this thread. Earlier, Charles informed us that the word 'tension' has a precise meaning in physics (and in engineering, too). He's right about that. I think it might be an idea to define it a bit more precisely.

Consider the blade of a hacksaw. It's installed in the saw frame, then screw fitting at the toe end is tightened to stretch the blade. The blade is now in tension - a uniaxial force pulling in opposite directions at each end, stretching it. Because the blade is stretched taut, it is less inclined to bend or twist. The same applies to a bow saw blade, or a coping saw blade. The force applied by the frame applies tension in the blade.

With a handsaw in normal use, there is nothing applying any force to it. It's just a piece of flat steel with a handle at one end - there's no frame applying any loads. Consequently, it's not in tension.

There are plenty of past writers about handsaws that have used phrases like, "shall possess the proper tension, spring or character", or talk about blades being 'tensioned'. They clearly don't mean placed in a frame of some sort and stretched - which would be the requirement for the proper definition of the word 'tension' to be fulfilled - so what do they mean when they use the word? That's what I'm puzzling over.


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## D_W (22 Feb 2016)

Cheshirechappie":2d6v8em6 said:


> worn thumbs":2d6v8em6 said:
> 
> 
> > Bob Smalser covers the topic well.The topic reminds me of a presentation I saw back in the eighties from a company specialising in shot peening and focusing on the benefits of imposing a force on the surface of the material by impacting it with a lot of small blows.It seems to me that the principle is very similar and like Mr Smalser,I would suggest anybody keen to learn more should seek out a cheap,distorted saw to help them understand the process.
> ...



The tension in old handsaws exists at the surface of the steel. You can grind it off if you get a rusty saw and are forced to remove too much of it.

This topic is quickly getting to a dead end of hypotheticals and what ifs, the saws are out there for you to try. you could even confirm your findings by striking floppy saws and comparing them to the hardness of a good sample like a disston. You're not going to find an answer with modern saws, as none of the modern makers are making a similar quality hand saw to what disston was making in the early 1900s (and to my knowledge, none is tensioning a saw).


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## D_W (22 Feb 2016)

Cheshirechappie":2qih5qt8 said:


> There are plenty of past writers about handsaws that have used phrases like, "shall possess the proper tension, spring or character", or talk about blades being 'tensioned'. They clearly don't mean placed in a frame of some sort and stretched - which would be the requirement for the proper definition of the word 'tension' to be fulfilled - so what do they mean when they use the word? That's what I'm puzzling over.



They are talking about stiffness of a saw, since proper tension makes the plate stiffer and reduces the chance of binding or kinking - which are not just threats to the saws, but are really annoying to a sawyer who cannot saw freely without worrying about binding a saw.


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## Cheshirechappie (22 Feb 2016)

D_W":7btlraf2 said:


> The saws were identical in size - 26 inch 5.5-6 point rip saws that are about 40 thousandths at the tooth line mid/back, and maybe slightly thinner at the to. Similar thickness at the top of the taper.
> 
> One saw was a disston 7, the other generic with no mark and a warranted superior medallion (but it was old enough to have a nib).
> 
> ...



David - I'm happy you like your Disston, but the answers you give to the questions I asked you about your two saws are that they are dimensionally similar (not necessarily exactly the same), but beyond that, don't know. Consequently, we don't really know what you're comparing.

I'm aware of Rob Streeper posting on the Australian forum, but as far as I've read so far, all he's done is hammer some saw blades. I'm not aware of his having compared the performance of a hammered (or rolled, or whatever) blade with an identical unhammered (unrolled, whatever) one, which I think is probably the best way to eliminate the hypotheticals.


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## D_W (22 Feb 2016)

I have no clue what you're going for, but you need to take your engineer hat off for this, because you're attempting to do what engineers often do on woodworking forums, and that is replace several hundred years of industry experience and customer preference with a poorly designed simplified test. 

You cannot hammer modern steel and declare it tensioned in the same way as disston or others would've done. You need to take two saws with similar hardness and similar plate dimensions and steel volume and saw with both. I have done that. The two saws that I am referring to are almost exactly the same in dimension - length, plate thickness, plate height, etc. 

You are unlikely to find someone who knows enough about tensioning a hand saw (at least remotely as well as was done by disston) to draw a reliable conclusion. You may draw a conclusion, but expect that anyone with experience will disregard it as yet another oversimplified "engineering" test that doesn't prove much in terms of trying to extrapolate the results as a conclusion for all saws. Understanding application of simplified tests and their use seems to be a problem for engineers - I've seen it on other forums, and Rob was equally confused in trying to state results from simplified tests that disagreed with historical actuality. 

One that I think he may still hold on to is the idea that he's got spring steel saws that are tempered to mid 60s RC. Don't fall into it. Get some vintage saws and try them and then measure them. If you get first and second or third line saws, I guarantee you fill find the difference between a well tensioned saw and one of the same hardness that is not well tensioned.


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## blackrodd (22 Feb 2016)

Not had time to read all replies, so I hope I'm not going over too much old ground.
I wasn't in the saw shop long enough to know all this, and unless I can find my night school/College books, which taught us to understand why we did, or did not follow certain procedures, in use the various saws, bandsaws, etc.
As I understand it, we all know There are different types of steel, I've posted a pdf which helps to show the different uses.
In a circular saw blade, I think this was achieved by different amounts of carbon, etc and tempered by heat treatment.
Hence the wobbling saw blade when burnt.
As I see it, The hacksaw mentioned will cut mild steel, and will not bend easily and is easy to break, 
Which is opposed to ordinary mild steel which is quite easy to bend, meaning different amounts of carbon content.
The handsaw was different again and has to stay stable in it's length and cut in a straight line under some force.
Obviously The superior saws of old were taper ground from best carbon steel hard enough to stay sharp, soft enough
to file and set without teeth snapping.
Regards Rodders

http://www.eng.utoledo.edu/~tschrede/me ... it%206.pdf


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## MIGNAL (22 Feb 2016)

I'll get my violin bow out and see if I can draw a sweet note from my new Spear and Jackson (far east) panel saw. 
It's always seemed to be a bit floppy to me, even though the steel is thick enough. I'll check but I think it's taper ground too. Once sharpened it cuts OK but something doesn't seem quite 'right' compared to the few similar vintage saws that I've used. Could be psychological, I don't really know. Maybe tension isn't the correct word but perhaps there is something else going on that's a result of the production process.


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## Cheshirechappie (22 Feb 2016)

D_W":20ckforw said:


> You cannot hammer modern steel and declare it tensioned in the same way as disston or others would've done.



Why not? What part of 19th and early 20th century saw manufacturing are we in the 21st century (even us simple-minded professional engineers) incapable of understanding?


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## D_W (22 Feb 2016)

Cheshirechappie":3clk0ctt said:


> D_W":3clk0ctt said:
> 
> 
> > You cannot hammer modern steel and declare it tensioned in the same way as disston or others would've done.
> ...



This is sort of like the question of sales coming to engineering and asking why they can't do a final engineering review and signoff. I am not an engineer, but I am in a technical job and I have come across the same thing ("I'm going to take this to clients, tell me what I'd need to tell them if I was an expert"). Not going to happen over night or by chance.

If you don't know why things that were improved incrementally over hundreds of years can't just be chanced upon, then you first need to get to the point of realizing that before moving on to creating simple tests. 

Rob has hammered saws some, I intend to try it at some point, but I don't expect that I'll duplicate disston's 1900 era efforts or saws made by english and US makers in the early to mid 1800s would have already done that (and they didn't). Neither Rob nor I nor probably almost anyone else will know enough about tensioning saws to duplicate what disston's rollers could do.


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## Cheshirechappie (22 Feb 2016)

Get some saws and try, eh?

Must admit I'm puzzled by this. I've been bothering bits of wood, on a strictly amateur basis, for thirty years now. In that time, I've used a few saws, and in recent years obtained a small selection from everybody's favourite interweb auction site, including a couple of bent ones that I managed to clatter straight. Maybe I'm just a completely insensitive dolt, but my findings about what makes a good saw over those years are firstly, sharp; secondly, straight (keeps to a line much better than a bent one); thirdly, comfortable handle; fourthly, weight - you can keep going longer with a lighter saw. I used to think taper grinding was important, until I used a hardpoint. It ate wood at an almost frightening rate, easily the match or better than any of my resharpenable saws - well, it did when it was new. Not quite so good when it lost it's sharpness.

Of the saws I have, the heaviest tend to be the thickest. One of the thick ones is a 1980s Robert Sorby Gilt Edge with the words "Tensioned Taper Ground Blade" printed on the blade. Horrible handle. It works, but it's not a nice saw to use. The thinnest, and most flexible (dare I say, floppy, even?), is a vintage Groves, which is a make everybody raves about as being about the best. It's a very nice saw - light for it's size, with a kerf a bit thinner than most saws of the size. Then there's my panel rip, converted from a 22" Spear and Jackson Spearior blade that cost me £6 including postage - that was one of the ones I had to flatten. It's a lovely saw to use - as all panel saws are, light and easy on the arm. It can't be 'tensioned' given the hammering (literally) I gave it to straighten it, but it saws beautifully.

Maybe I'm a completely insensitive dolt, but I do wonder - from my experience of sawing, anyway - just how much difference 'tensioning' really makes, or whether it's one of these things the marketing departments plugged, and tool obsessives drool over, in much the same way that some insist that only the everlasting grades of steel are good enough to make a chisel. I do know that my saws saw, they saw to a line without much bother, the lighter ones to use tend to be the thinner ones, and they all work much better when they're sharp.

But still - what would I know? I'm only an ignorant engineer.


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## D_W (23 Feb 2016)

I can spot an engineer on a forum from a mile away, and not only this one, because this kind of thing applies (attempting to set up a straw test and draw a universal conclusion) and happens all the time. 

I don't think your saws are representative of a quality lot of saws from the 1900s or so. I don't know anything about groves saws other than that I have a groves rip saw, and it's not floppy at all. Anything made after 1935, I'd question the quality - saws were in a downward spiral of cost cutting running from circular saws. 

Maybe the saw market is less uniform in the UK. In the US, 80% of the saws directed toward professionals were disstons, probably the bulk begin no 7s and D8s. There are plenty of second line saws to compare them to. I'm less familiar with what is first and second or third or worse in sheffield. 

I have no clue what the context of your use is, but the only way you get a real sense for saws is to use them for everything in several projects (rough ripping, fine ripping, resawing, etc). If you're using them as an ancillary tools to power tools, you can tolerate a lot of substandard characteristics, just as people can easily forget about how excellent a double iron plane is if they only use their bench planes to smooth already machine planed wood. 

At any rate, if you shoot for drawing a universal conclusion before you have more exposure than the saws you list, nobody will have any regard for the conclusion, anyway. The forums are full of people who assert something that is the opposite of what people have known for a hundred or more years. Most people won't use saws enough to know what's correct or not, anyway, you may become a guru and have your results parroted on the other guru's blogs. If I were you, and I saw all of the old texts discussing tension, I would spend more time trying to figure it out and less trying to say it doesn't exist.


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## D_W (23 Feb 2016)

I have been on the wrong side of these things, by the way, stating that old text was vague and what was behind it was hot air. On oilstones, on double iron planes, etc. 

That's partly what makes me less apt to just write off older common knowledge even though I haven't tensioned a saw myself yet (but do have similar hardness saws with similar cross sections that are way different in stiffness - which would be due to ____ if it's not tensioning?).


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## CStanford (23 Feb 2016)

Why would Disston hire, train, and pay the skilled labor required to do this step in the manufacturing process if it weren't necessary? For $hits and giggles?

If it weren't necessary I'm thinking somebody would have noticed.


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## D_W (23 Feb 2016)

CStanford":3ujegheb said:


> Why would Disston hire, train, and pay the skilled labor required to do this step in the manufacturing process if it weren't necessary? For $hits and giggles?
> 
> If it weren't necessary I'm thinking somebody would have noticed.



in 2015, they could target white collar retirees with a scheme like that, but not in 1900.


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## CStanford (24 Feb 2016)

If there was (is) nothing to tensioning then it was one of the biggest marketing ruses of all time -- complete with employees doing faux work but being paid real salaries, etc.

Or maybe they really were that stupid back then. Nah, doubtful.


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## Carl P (24 Feb 2016)

I've found this discussion very interesting and while I know nothing about it, it seems to me that the term 'tension' may be something of a misnomer, possibly stiffening may be more descriptive. Also, as to evidence, unless you can tension a saw yourself, no matter how many saws you may try, because of the variables, all you can really prove is one saw is better than another as in 'the plural of anecdote is not data'. Some kind of test would be essential, grinding down the saw plate will, naturally, make it more floppy, it being thinner and all, and may change the hardness, so is somewhat pointless. The only meaningful test I can see would be to make two identical saws, but with only one tensioned. Alas this is very much beyond my meagre capabilities, so I'll leave that to someone with actual talent, until the results of such a test are known, most of what can be said on the matter seems so much unsupported hot air.

Cheerio,

Carl


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## AndyT (24 Feb 2016)

I've enjoyed it too. I'm no physicist or engineer, but I now have a new mental image of what might be going on inside an old saw blade, which I think fits in with what used to be done in manufacturing.

First, think of a concrete beam. It has some resistance to bending, but not much. When it is supported at the ends and loaded in the middle, it sags down, with the upper parts in compression and the lower parts in tension.

To make a stiffer beam, you can insert steel rods, and pull on opposite ends while the concrete sets around them. The result is a pre-stressed beam. The pull (stress) in the steel does not move anything but it is real, and helps counteract the stretching that would happen to the underside when a load is applied. So we have a concept of an internal stress, which helps keep the beam straight (makes it stiffer).

I think this is what the skilled saw smiths were doing. By hammering, some of the steel was put in a state when it would have stretched out longer, but could not, because it was constrained by other areas of steel around it. They made these small areas of different stress across the whole saw, in a balanced way.

It's extra complicated because forces within the steel on one face of the plate need to be balanced by forces on the other face, or else the plate would bend - and the plate is very thin.
It's extra complicated because the steel was made in small batches and was not as consistent in its internal chemistry and structure as modern steel can be.
It's extra complicated because the saw went through repeated grindings and heatings, which would have affected its stiffness and elasticity.
It's extra complicated because the areas wanting to expand are small and not visible, as are the unstretched areas constraining them.

So, in my imagination, I now see the saw plate as something like a lattice structure (think of a railway bridge) where short elements are variously in tension or in compression, but the whole structure ends up being strong, with the right balance between stiffness and elasticity. 

And the reason that this tensioning is not done any more, is that modern strip steel is so much more homogenous and reliable that it is not needed.

Does that make sense to anyone else?


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## CStanford (24 Feb 2016)

Carl P --- "the plural of anecdote is not data" Priceless!


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## CStanford (24 Feb 2016)

Shot peening:

https://en.wikipedia.org/wiki/Shot_peening

"Shot peening is often called for in aircraft repairs to relieve tensile stresses built up in the grinding process and replace them with beneficial compressive stresses. Depending on the part geometry, part material, shot material, shot quality, shot intensity, and shot coverage, shot peening can increase fatigue life up to 1000%.[2]

Plastic deformation induces a residual compressive stress in a peened surface, along with tensile stress in the interior. Surface compressive stresses confer resistance to metal fatigue and to some forms of stress corrosion.[1] The tensile stresses deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start in the interior."

With saws perhaps tensile stress is a desired characteristic whereas for aircraft bodies, wings, etc. it is not. By striking the saw plate on both sides, equally, rather than relieving tension it increases it.

Things do apparently happen when metal is struck and these things are not necessarily obvious to the naked eye. That is, unless a big crack opens up in an airliner at 35,000 feet.

I think the old guys knew what they were doing. Maybe it isn't necessary these days because of the raw material and processes available but those old saws, when in good fettle, do seem to have a little something 'extra' that modern saws do not -- not a huge difference, but there is something there.


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## D_W (24 Feb 2016)

Carl P":2u1uxyir said:


> I've found this discussion very interesting and while I know nothing about it, it seems to me that the term 'tension' may be something of a misnomer, possibly stiffening may be more descriptive. Also, as to evidence, unless you can tension a saw yourself, no matter how many saws you may try, because of the variables, all you can really prove is one saw is better than another as in 'the plural of anecdote is not data'. Some kind of test would be essential, grinding down the saw plate will, naturally, make it more floppy, it being thinner and all, and may change the hardness, so is somewhat pointless. The only meaningful test I can see would be to make two identical saws, but with only one tensioned. Alas this is very much beyond my meagre capabilities, so I'll leave that to someone with actual talent, until the results of such a test are known, most of what can be said on the matter seems so much unsupported hot air.
> 
> Cheerio,
> 
> Carl



I think you're off base still on one thing - if nobody knows how saws were tensioned, then your test wouldn't prove anything. 

I suggested finding two stiff saw plates, one a hundredth thicker than another or so so that you can take the thicker plate and grind it down to the size of the thin plate. Tensioning is in the surface and that would remove it. That should leave someone with two saws that were formerly tensioned of different sizes, but the ground saw would match the first saw and presumably be floppy. 

What I suggested would be more relevant - find two saws that are the same cross section in metal (i.e., the plate sizes are about the same) and that are the same hardness, search until one is floppy and one is not. If those things are all true (same plate size/thickness and same hardness), what else would someone think is occurring. These are water or oil hardening steels we're talking about, there's not mystery making them stiffer other than physical working of the steel. 

OR, to my knowledge, there are a very few remaining sawsmiths in japan making saws entirely by hand. You will read in some places that there are non, but stan covington on another forum knows a guy who makes about 20 saws a year entirely by hand. Ask the guy about tensioning, see what he says. As charles says, you can believe he's tensioning a saw for no reason, or you can take the much more probable view that he knows what he's doing and you can learn something from him. 

A "talented" amateur reproducing what took the saw industry a century to perfect in manufacturing is not a good test. First, the amateur has little chance of getting things as right as a history of progressive improvement, and second, they have zero ability to do tensioning the way it was done in manufactured saws (which, of my use, were better and more consistent than the more handmade saws from an earlier era).


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## D_W (24 Feb 2016)

It's suggested that it's "not needed" due to the homogeneous 1095 available now, but to assume that the current batch of steel is a lot better or more homogenous than the house steel disston would've used is suspect. It was probably made with a similar process. 

I've got a roll of 1095 that is 4 inches tall and 0.042" thick. It's stiff compared to unhardened steel, but not stiff compared to a saw made in 1900 or so. 

I wouldn't trade a 1900 D8 for a modern boutique carpenter's saw, even without the price difference. Modern backsaws are a better bet because there's no need to tension a plate held in a saw back.

When someone doesn't notice the difference between various saws, I wonder how much they're sawing - dovetails? sticking? crosscutting boards here and there? It's sort of like someone who only smooths weighing in on the important aspects of a fore plane.


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## AndyT (24 Feb 2016)

D_W":22pgsfin said:


> It's suggested that it's "not needed" due to the homogeneous 1095 available now, but to assume that the current batch of steel is a lot better or more homogenous than the house steel disston would've used is suspect. It was probably made with a similar process.



Ok, how about, "now that steel strip is sufficiently consistent in its characteristics to make a decent saw, further treatment by hand hammering would cost more than the market would bear, given the very small number of new saw purchasers who would appreciate the marginal improvement and be willing to pay the large amount it would cost, given that the skill and knowledge needed to tension saws by hand have virtually disappeared."


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## CStanford (24 Feb 2016)

That pretty well sums it up Andy. Plus, people already pay a lot of money for boutique saws that have not been hand hammered. Assuming one has all the orders one can handle, has apparently distinguished his firm from the crowd, there would be nothing much to gain.


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## Rhyolith (24 Feb 2016)

To me, what Andy described (about the lattice structure) makes sense. There are other examples where there are forces present within a single piece of steel, such as plane soles where the annealing process is used to remove/manipulate them for better overall performance of the tool. I do not see why it is not possible to manipulate them to the overall benefit of sawing in a hand saw too. We know that hacksaws benefit from a stretched/tensioned blade so its not much of a jump to assume panel saws would benefit in a similar way (why wouldn't they?); particularly if the steel was not very uniform to start with. So as far as I am concerned it probably could have been done and defiantly would have been beneficial. 

The only question in my mind is *can stretching/tensioning the blade in the manner that a hacksaw frame does be have been done in a Panel saw?* to answer that I/we need to ask *How?* And that can only be answered by a actual saw maker. So has anyone got any contacts on this front? 

Further: I really think the argument of whether the type of stretching/tensioning mentioned above (like a hacksaw) of benefit is a red herring... of course it would be just try sawing with an un-tensioned hacksaw to see that :? *The debate is whether that is what "tensioning" means in a saw makers context (what it means in physics is irrelevant, science is a language on to itself) and how it was done. *


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## CStanford (24 Feb 2016)

I guess the forum's next move is to try to identify a maker of new saws who is tensioning by hand-hammering. Might be a tall order.

I suppose an old 'saw doctor' would suffice as well. We have all Bob Smalser has written on the subject unless he could be encouraged to post on this forum and in this thread.


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## MIGNAL (24 Feb 2016)

I've tried tapping on my saws with the knuckle. All the new saws ring like a church bell (even the back saws), my old saws don't! 
Unfortunately I don't have enough examples of old saws to make it a meaningful test. It's probably not a meaningful test anyway but if someone catches you listening to the sound of an old saw at least you'll be termed eccentric. They just might use a slightly stronger term of phrase though.


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## D_W (24 Feb 2016)

AndyT":11q58txe said:


> D_W":11q58txe said:
> 
> 
> > It's suggested that it's "not needed" due to the homogeneous 1095 available now, but to assume that the current batch of steel is a lot better or more homogenous than the house steel disston would've used is suspect. It was probably made with a similar process.
> ...



That's pretty fair. I would sum it up as if the customer can't tell the difference, then why bother with the expense?


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## Cheshirechappie (24 Feb 2016)

D_W":1804rnkf said:


> AndyT":1804rnkf said:
> 
> 
> > D_W":1804rnkf said:
> ...



Or perhaps, if the customer can't tell the difference, there isn't one.

One thing that does occur to me is that if somebody had discovered a process that made thin metals stiffer, it would have had huge commercial potential in many other fields of engineering. Aircraft work, for example, in which it might have reduced or eliminated a great deal of the expense and trouble of fitting stiffening ribs, and eliminated their additional weight. Automotive body panels are another application that springs to mind. Engineers (and especially business accountants) are always looking for ways to do things using less material. That no such process exists (well, to my knowledge, anyway) suggests that the difference it made to a sawblade wasn't especially dramatic.

Also bear in mind that sawblades had to be hammered to straighten them after heat treatment, the processes at the time being incapable of producing flat, hardened and tempered stock, which is something the steel mills can do now, as Andy says. The understanding of material science, stresses and metallurgy was even more imperfect in the late 19th century (indeed, it was pretty much in it's infancy then), so the use of words in a technical context tended to be very loose by modern standards. They very probably looked at springs and thought of 'tension' - hence phrases like 'proper tension, spring and character'. Just meant 'springy' to them - which is, after all, what you're after; flat, and springing back to flat if deflected.


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## D_W (24 Feb 2016)

I'll pose a scenario:

* A 1900s customer who worked professionally with saws (without the help of power tools, often on site work) could tell the difference and would pay for it (despite having very little disposable income)
* A modern hobbyist can't tell the difference

So the odds on favorite is .....to start by assuming the hobbyist is correct? 

I can tell the difference, and i'm only a hobbyist. But I use my saws for everything - ripping, crosscutting, resawing. And it is in ripping and resawing that the differences become so stark, and for the same reason, conversion of a saw designed for crosscutting isn't always a great choice for creating a fine-toothed ripping saw. 

We have no chance of recovering what disson knew about tensioning handsaws at a commercial level. We may have some hobbyist makers or boutique makers who would like to recreate a different process using hammers, something that could've been done prior to perfecting rollers (and was probably done). 

We're talking about the same audience who pretty much was universally sold, for a while, on a plane having an extremely thick single iron, bevel down, as being tops for functional planing (but for some reason, planes weren't made that way 125 years ago). 

The buying audience these days isn't very demanding, especially the people actually spending money. Those are the folks who are just coming into the hobby after making a living elsewhere and having discretionary money to spend.


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## Cheshirechappie (24 Feb 2016)

Ah - so you can tell the difference, but the rest of us modern hobbyists can't....


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## MIGNAL (24 Feb 2016)

http://www.crosscutsawyer.com/viewtopic.php?f=4&t=750


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## Cheshirechappie (24 Feb 2016)

MIGNAL":2q6aa1ft said:


> http://www.crosscutsawyer.com/viewtopic.php?f=4&t=750



Interesting.

One question it doesn't answer is what difference there is between a blade so rolled and one not. If any.


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## Rhyolith (24 Feb 2016)

MIGNAL":2frmzlpo said:


> http://www.crosscutsawyer.com/viewtopic.php?f=4&t=750


Yes, that is interesting!  Its still a bit vague though, do you have an account on that forum? maybe could ask for some details on the process of tensioning? Might finally answer some of the questions rolling round this thread (thank you all for the debate and input by the way, I found it very good read  ).


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## MIGNAL (24 Feb 2016)

No account. I wasn't even aware that a forum existed specifically for crosscut sawing! 
It has been an interesting thread. I'd certainly heard of 'tensioning' saw plate but I've never known anything about it. I'm not sure that I've ever believed it existed. In truth I probably haven't paid any attention to it. Planes are my thing. Saws are for my next life.
Someone needs to join and PM that French chap Diabolo. No doubt he'll have more to say on the matter, especially since he seems to be a saw maker, even if not in a commercial capacity.

There's also mention of it on the following, especially the final post on the difference in steel. (post 16). Stephen Shepherd is the guy who wrote a very good book on traditional Finishes and a very good book on Hide glue. 

http://www.fullchisel.com/blog/?p=137


Assuming this hammering did take place (and I've no idea either way) when did it stop? Roughly, when did saw plate stop getting hammered and when did it become rolled? Is a Disston from eg. 1935 inferior? 
Presumably it wasn't only Disston that was doing this and it applies to other makers of quality saws.


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## Rhyolith (24 Feb 2016)

Aren't Dissiton still about? I thought they were? 

Also I thought Lie-Neilsen claimed to tension saws (have not checked that yet)... i vaguely remember someone i knew having a problem with a small LN tenon saw and it being fixed via tensioning... but I cannot remember the details so don't rely on that account. 

Thanks for the link Mignal, will read it tomorrow... bed time for me should have been 40mins ago


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## Cheshirechappie (24 Feb 2016)

Yes - it's all speculation at the moment. Lots of questions, no answers (though it seems some are more certain about things than others).

I suppose in the fullness of time, somebody will work it out. After all, the skills of making moulding planes disappeared. I dare say some said the skills had gone for ever, and we'd never replicate what the old makers could do. Then along came Clark and Williams, Matt Bickford, Philly, Caleb James.....not to mention John Whelan and Ted Ingraham, and probably several others. If it's been done before, it can be done again.

I still think the clincher will be if somebody produces two identical saws, one 'tensioned' and one not, and demonstrates a significant difference. Until then, it's all hot air.


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## Rhyolith (25 Feb 2016)

Cheshirechappie":2vg1sge1 said:


> I still think the clincher will be if somebody produces two identical saws, one 'tensioned' and one not, and demonstrates a significant difference. Until then, it's all hot air.


I see where you coming from with this, but I think there are too many variables for a test like that to be meaningful. For example: User's: skill, psychology, preference, physical capabilities, past expierence. Saw's: Metallurgy, past treatment, overall age, sharpness, size, weight.... etc. There are just to many that you cannnot be certain about in an old saw alone (prove me wrong here) and thats not even including the huge influence the user has. 

Plus as we don't actually know for certain what tensioning is yet, so how can we know one of the saws is tensioned (properly)? Particularly as all the examples seem to be 100 years old. So for me the clicher is definalty finding that out.


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## Cheshirechappie (25 Feb 2016)

Rhyolith":31kfsuvz said:


> Cheshirechappie":31kfsuvz said:
> 
> 
> > I still think the clincher will be if somebody produces two identical saws, one 'tensioned' and one not, and demonstrates a significant difference. Until then, it's all hot air.
> ...



Just to clarify, I didn't mean that somebody compares two vintage saws. What I meant is that somebody takes some new spring steel and makes two new saws from it, one 'tensioned' and one not. If there is a noticeable difference between the two in performance, or stiffness, or waviness of the toothline when it gets hot, or whatever, then it's clear that the 'tensioning' has done something. The maker would also know exactly what they had done differently with the two saws, and could describe the process, if not the exact metallurgical effect.

I suspect there may be a bit of 'suck it and see' involved in this. The links Mignal posted suggested some sort of rolling process rather than hammering, but the point of controlled testing is that you try something on one workpiece and compare with an identical workpiece not so treated to see what the effect is. It may be that quite a few controlled tests along these lines are needed to work out which is the most effective - or it may be that it demonstrates that none of them are particularly effective.

A fun project for somebody!


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## AndyT (25 Feb 2016)

I'm away from books again, but perhaps someone could check what our best saw historian, Simon Barley has to say on this. I think it's that final tensioning was only done on the top grade of saws, not on the second or third grade. That would fit with the collective idea that it's something not everyone would notice or appreciate.


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## Cheshirechappie (25 Feb 2016)

Simon describes 13 steps in the manufacture of saws.

1) Preparing the flat sawplate.
2) Paring, toothing and marking.
3) Hardening and tempering.
4) Grinding.
5) Smithing.
6) Further grinding, glazing and smithing.
7) Rubbing.
8) Blocking.
9) Stiffening.
10) Setting and sharpening.
11) Fitting the back.
12) Handling.
13) Packing and despatching.

The most relevant section is probably section 5, Smithing. Simon writes, "The saw plate might at this stage to the uneducated eye look flat, but it contained multiple and almost invisible irregularities which the trade called 'fast' and 'loose'. These were corrected by a saw maker's hammer that had two faces at right angles to one another and which produced the marks shown in figure 1.13 [The marks look rather like chequer-plate, for those familiar with it.] The sheet also had to be hammered to produce stretching of the edge and hence "tension", in order to increase its ability to return to straightness when bent. Flatness and tensioning were achieved by the smith's hammering in one place after another, and on both sides, constantly checking for the right result using a sawmaker's straightedge (figure 1.14)."

Under section 9, Stiffening, he writes, "Although there is no mention of this stage in the statement of prices, it appears always to have been part of the manufacturing sequence in the Sheffield saw industry. It involved heating the sawplate up to a fairly cool red heat, thereby restoring the flexibility that had been diminished by rubbing and blocking. There are indications in one manufacturer's advertising material from the 1970s that stiffening was reserved for the best of their four qualities of handsaws. A stiffening trough was also referred to in the Wilson saw stock inventory of 1774, but there is no other information to enable us to know how or at what stage it might have been used at that time. In the account of saw manufacturing at Spear and Jackson's works in 1861, stiffening was described as coming after setting."

Which suggests that there was a process of hammer tensioning of some sort, carried out during the plate flattening stage (or one of the plate flattening stages, more accurately). How much difference it made, and whether it was done to all saws, isn't stated, and figure 1.14 shows smiths working on circular saws, not hand saws. 

However, the description of 'stiffening' is very confusing. Heating a near-finished saw blade to a red heat, even a fairly cool one, is most likely to anneal (soften) it, and certainly won't stiffen it. It may have been a way of recovering plates that wouldn't flatten easily by annealing them to take out all the hammer stresses put in, before re-hardening and tempering, and then going through the processes again - but that's just me speculating. 

Again, more questions....


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## D_W (25 Feb 2016)

AndyT":j2spp7di said:


> I'm away from books again, but perhaps someone could check what our best saw historian, Simon Barley has to say on this. I think it's that final tensioning was only done on the top grade of saws, not on the second or third grade. That would fit with the collective idea that it's something not everyone would notice or appreciate.



That goes toward my earlier comment, too, about similar hardness saws not being similar in stiffness. I've not noticed the floppiness I described other than on unmarked saws, but I have to admit I don't have any mid-line saws. Just saws that are old enough to be pre-roller tensioning.

The japanese describe tensioning as a separate step from straightening, also, and at least in one place, I saw it described as ensuring that the plate stays straight.


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## D_W (25 Feb 2016)

Cheshirechappie":1foiz021 said:


> Rhyolith":1foiz021 said:
> 
> 
> > Cheshirechappie":1foiz021 said:
> ...



The trouble with your test is that it can only prove that tensioning is successful if someone who is not skilled in it can find a result. Your initial hypothesis suggests or at least implies that you think there's a great chance that it doesn't do anything. your test can't prove with any reliability that it doesn't stiffen a saw plate or provide some other benefit, because failure of someone who has no clue what their doing isn't proof that something doesn't work. 

The best tensioned saws (with more language coming in later posts that it was reserved for higher lines of saws just supporting what I've already noticed, but you discount, anyway) were done with rollers. that's my experience. Saws like a Disston #12 or even the older D8s (which are wonderful saws, despite their ugly appearance and gigantic handles - unequaled by anything anyone is making now).


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## ED65 (25 Feb 2016)

Very late to this thread but just wanted to go back to something way back on the first page which might be critical.



Cheshirechappie":3etfnz8i said:


> Edit to add - the only way I can think of to make a sawblade stiffer (other than to make it a backsaw) is to make it from thicker material to start with. Stiffness of flat pieces of material is proportional to the cube of their thickness, so not much thicker makes it significantly stiffer. Conversely, not much thinner makes it significantly more flexible.


How about increased harness? As might be created by work-hardening the steel. 

This is a well-understood process among traditional panel beaters and the steel used is quite similar. Edit: also with the making of steel drums. I can't imagine some hardening not occurring when hammering a saw, although the magnitude of the effect is likely a lot less since the changes in shape are so much more limited. 

I agree incidentally that the use of the word tension _might _be a red herring, older written sources are a minefield when it comes to this sort of thing both with regard to modern technical usage of the same term and how it might be used in day-to-day speech. However, I'm not convinced there's no internal tension in a well-made traditional saw plate, sorry


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## ED65 (25 Feb 2016)

Carl P":3ksnwalt said:


> as in 'the plural of anecdote is not data'.


That's a good one, love it!

But actually, it can be. Multiple anecdotal accounts are a form of data, they can't simply be discounted particularly when there is some consistency. I'm not saying we accept it blindly, it must be confirmed by further testing of course. But that's not to say it is being discounted as data, after all scientific test data must also be confirmed.


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## D_W (25 Feb 2016)

ED65":1dzsr95v said:


> But actually, it can be.



Presuming my comments about the stiffness of actual saws are being called an anecdote (as well as the writing - I don't follow that much of historical writings, etc, you have to know if the source was a writer turned toolmaker or a toolmaker turned writer, etc). 

My comments are a data point (as are any others where someone has actual experience), and not an anecdote.


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## Cheshirechappie (25 Feb 2016)

ED65":1om23m6c said:


> Very late to this thread but just wanted to go back to something way back on the first page which might be critical.
> 
> 
> 
> ...



You are quite right that the phenomenon of work-hardening exists. Indeed, it was used in the 18th century to make cheap saws from sheet iron - the soft iron was hammered until it became springy. One of the contemporary writers (Moxon, if memory serves) warned against the purchase of such saws, stating that they were much inferior to steel ones.

Panel beaters normally work with low-carbon steels rather than the high-carbon steel used to make springs and saws, but they do encounter work-hardening, having to anneal work (heat it to red heat and allow to cool slowly) before they can carry on. Saw steels are a bit different, in that they are deliberately heat-treated to a fairly high degree of hardness before any hammering takes place, so there's much less scope for increasing hardness by hammer work. It will happen to some extent, though, and if saw blades are over-hammered (or worse, bent sharply, then bent back by hammering), the increase in hardness can be sufficient to push the steel to it's upper limit of tensile strength, and a crack - a catastrophic failure in engineer-speak - will occur. The same can happen if a set tooth is bent the 'wrong' way.

You're perfectly entitled to your opinion on internal tension in a traditional well-made saw blade - and at least you expressed it politely! My position remains, as it has been throughout the discussion, open-minded but sceptical. The links Mignal found certainly provide some interesting material, though as the first suggests that 'tensioning' was done to reduce the likelihood of a saw developing a wavy toothline if it became hot, and Simon Barley's writings suggest that it was to give a saw the capacity to return quickly to straight if bent, there still seems to be some - well, lack of clarity, shall we say.

No doubt in the fullness of time, the problems will be solved and the questions answered!


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## Rhyolith (25 Feb 2016)

I really really want to know what saw tensioning is now... as I am pretty much convinced it exists. 

Can someone post a photo of a saw that is defiantly tensioned? I am just curious to see one (I do have a few old Dissitons, but I know little about them).


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## D_W (25 Feb 2016)

Rhyolith":o2cysnln said:


> I really really want to know what saw tensioning is now... as I am pretty much convinced it exists.
> 
> Can someone post a photo of a saw that is defiantly tensioned? I am just curious to see one (I do have a few old Dissitons, but I know little about them).



Any disston #12 or D8 (at least the older D8s...I have one newer D8 that has a shorter plate and it's less stiff, even accounting for the plate height). 

Even the #12 small panel saw that I have for crosscut has excellent stiffness (a 24 inch saw that's 11 point), despite having a smaller plate cross section than some larger crosscut saws that I have. It files like any other saw (I have had saws that are hard enough such that they're really hard on files, but it's not one of them).

Of course, those were tensioned with rollers, so there's no evidence of the tensioning. 

Bob Smalser's write-up on saw tensioning describes what's occurring in the metal pretty well. Whether or not it does a 100% job of explaining what's going on, I don't know. 

re: earlier comments about a layer of hardened surface - that may be true, but it would be very shallow if it was there.


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## CStanford (26 Feb 2016)

And then there's 'retensioning' back saws:

http://www.badaxetoolworks.com/retension-a-backsaw.php


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## CStanford (26 Feb 2016)

Another useful link:

http://www.wkfinetools.com/tRestore/saw ... tAm-01.asp


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## Cheshirechappie (26 Feb 2016)

Charles - the first link is about the old trick of straightening out a slightly cockled backsaw blade by tapping the back of it's spine. Nothing about hammering the blade itself. The second link, if you read it carefully, is about getting hand saw blades flat and straight, and circular saws slightly dished to allow for thermal expansion of the edge and centrifugal forces at working speed. Neither link, if you read them carefully, makes any reference to the type of 'tensioning' under discussion here.


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## CStanford (26 Feb 2016)

The links are for general consumption. Somebody might find a nugget that strikes a chord, or make a logical inference you've decided you are unwilling to make. Resources are so few and far-between it makes no sense not to put them out there and let participants judge for themselves.

I don't see any of this as an argument per se, but if it is, it's certainly going to be one you'll 'win' by default if you get to make the final judgment about what does and does not apply.

Things that walk and sound like ducks are often actually ducks.


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## Cheshirechappie (26 Feb 2016)

CStanford":1rn0qvh8 said:


> The links are for general consumption. Somebody might find a nugget that strikes a chord, or make a logical inference you've decided you are unwilling to make. Resources are so few and far-between it makes no sense not to put them out there and let participants judge for themselves.
> 
> I don't see any of this as an argument per se, but if it is, it's certainly going to be one you'll 'win' by default if you get to make the final judgment about what does and does not apply.
> 
> Things that walk and sound like ducks are often actually ducks.



What sort of duck, though?

The problem with the word 'tension' is that it has a very precise late 20th and early 21st century technical and scientific definition, which didn't really exist in the late 19th century. Consequently, when reading late 19th century texts, one has to try and interpret the meaning the writer was trying to convey. For a start, they probably didn't mean "dramatic tension", and if you assume they mean "the state resulting from the application of a uniaxial force tending to stretch an object" the text often makes no sense at all, because there is no frame or mechanism to apply such a force.

Context, as so often, is all.


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## CStanford (26 Feb 2016)

Probably the physical state of a piece of sheet steel when certain areas are thinner than another.

Personally, I couldn't care less what it's called. My only concern would be the efficacy of producing such a condition in a saw blade. 

It's clear, I believe, that the major manufacturers thought there was something to it. I'm happy to give them the benefit of the doubt.

As to the change in meanings of words from the 19th to 20th to 21st centuries -- have fun with that.


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## Cheshirechappie (27 Feb 2016)

CStanford":273k99in said:


> Probably the physical state of a piece of sheet steel when certain areas are thinner than another.
> 
> Personally, I couldn't care less what it's called. My only concern would be the efficacy of producing such a condition in a saw blade.
> 
> ...



It's some effect connected with taper grinding, then, perhaps?

Earlier in the thread, D_W told us that whilst he could detect this difference, he thought the rest of us bumbling amateurs possibly couldn't. If you take that literally (not sure that I do, by the way), then the difference it makes is marginal at best.

The links Mignal posted seem to come closest to shedding light on the issue, but even they raise more questions than they answer. So far, there are some strong opinions, some head-scratching, but no solid evidence or proof either way. I don't accept the argument that Disston had a secret process, now forgotten, that could not be replicated in the modern world. If it's been done before, it can be done again. So far, nobody seems to have achieved it; nobody has demonstrated a noticeable difference between a 'tensioned' saw and an identical saw 'untensioned', which leads to some scepticism that it exists at all, or if it did, that it made more than a marginal difference.

Did 'tensioning' just mean the process of getting a sawblade flat and straight? Were Disston very good at marketing kidology in implying that their (granted, very good) saws had a little magic something nobody else knew about?

We don't know. If somebody can answer our questions, please do. Until then, it's just another rather pointless internet discussion bordering on argument, rife with opinion but short on solid evidence, as far as I'm concerned.


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## MIGNAL (27 Feb 2016)

In other news I used a Stanley speed cut yesterday (on some Oak). Amazing what a cheap bit of steel can do. Made this guy seem like he was cutting at snail speed.

https://www.youtube.com/watch?v=c_KGrltTSZg


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## CStanford (27 Feb 2016)

Chappie, what was it about the shot peening link I posted that didn't convince you that tension and compression forces are present in sheet steel and can be manipulated by striking it?

While shot may be more efficient, what is it about a hammer you think wouldn't accomplish essentially the same thing(s)?

"Shot peening is an important and, for safety reasons, an essential process in many industrial sectors, primarily in the aerospace and automotive industries.* Peening dates back to Bronze Age armourers;* although in more recent years, this technique has been used by engineers who worked the surface of a component with a ball peen hammer in order to induce internal compressive stress and thus increase service life."

"Shot peening is a cold working process used to produce a compressive residual stress layer and modify mechanical properties of metals and composites. It entails impacting a surface with shot (round metallic, glass, or ceramic particles) with force sufficient to create plastic deformation.[1][2]

It is similar to sandblasting, except that it operates by the mechanism of plasticity rather than abrasion:* each particle functions as a ball-peen hammer.* In practice, this means that less material is removed by the process, and less dust created."

"Shot peening is often called for in aircraft repairs to relieve tensile stresses built up in the grinding process and replace them with beneficial compressive stresses. Depending on the part geometry, part material, shot material, shot quality, shot intensity, and shot coverage, shot peening can increase fatigue life up to 1000%.[2]

*Plastic deformation induces a residual compressive stress in a peened surface, along with tensile stress in the interior. *Surface compressive stresses confer resistance to metal fatigue and to some forms of stress corrosion.[1] *The tensile stresses deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start in the interior."*


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## CStanford (27 Feb 2016)

S&J was apparently still hand-tensioning into at least the mid-20th century:

Spear and Jackson, Story of the Saw (1961) (PDF can be found at the Toolemera website).

In Sheffield, at Spear and Jackson's Aetna works,
Spearior quality hand and tenon saws and Mermaid
quality circular saws are all made from steel melted in
electric arc furnaces. The ingots to controlled analyses
and free from impurities are hammered or roll-cogged
to slabs (or 'cheeses', as circular saw slabs are called
in the trade), cross-rolled to plates in a sheet mill and
passed through blanking press or paring shop in an
annealed or soft state, and then go to the particular
production department. *The handsaw blank *is toothed
by rotary or reciprocating punch, hardened and
tempered, tested, hammered flat and* tensioned by
highly skilled smithers*, before going forward to be
ground and glazed.


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## Cheshirechappie (27 Feb 2016)

Shot peening can induce a compressive stress in the surface of a component, which is very useful because cracks can't propagate in a compressed surface. They can in one under tension. Thus, the technique can be used to increase the fatigue life of components, or to relieve fabrication stresses, such as those produced by welding operations.

If something like a saw blade has compressive stresses induced in the surface, they must be balanced by a tensile stress in the core. However, if the component is in equilibrium, the net effect on the whole is zero.

I can find no indication anywhere that shot peening a piece of metal will stiffen it - and believe me, I've looked. That's about an hour of my life I won't get back again!

As to the S&J link, it doesn't say anything about what 'tensioning' is, or what it does to the saw, so it doesn't really inform us any more than any of the other links.

By the way, I've been looking on the interweb for Disston marketing pamphlets and information. The ones I've found so far don't mention the word 'tension' at all in connection with saw blades. Can you, or anybody else, post a link or a photo of the relevant page of any Disston literature that does - it must be out there somewhere.


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## Cheshirechappie (27 Feb 2016)

Rhyolith":3nt9kfmt said:


> Aren't Dissiton still about? I thought they were?
> 
> Also I thought Lie-Neilsen claimed to tension saws (have not checked that yet)... i vaguely remember someone i knew having a problem with a small LN tenon saw and it being fixed via tensioning... but I cannot remember the details so don't rely on that account.
> 
> Thanks for the link Mignal, will read it tomorrow... bed time for me should have been 40mins ago



Yes - Disston are still about, but they don't make handsaws - http://www.disstonprecision.com/


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## Rhyolith (28 Feb 2016)

Cheshirechappie":137nkaut said:


> If something like a saw blade has compressive stresses induced in the surface, they must be balanced by a tensile stress in the core. However, if the component is in equilibrium, the net effect on the whole is zero.


This is exactly how I think tensioning works. If the tensile stress on on the cutting edge, then too all instensive purposes its stretched like a bow saw blade. This stretching of the blade in bow saws something of known benefit and without doubt makes the saw cut better, so why wouldn't that work in Handsaws?


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## D_W (29 Feb 2016)

Cheshirechappie":2cs6m3ol said:


> Earlier in the thread, D_W told us that whilst he could detect this difference, he thought the rest of us bumbling amateurs possibly couldn't. If you take that literally (not sure that I do, by the way), then the difference it makes is marginal at best.



I'm a bumbling amateur, too, but I guess that in the recent past, I've done a fair amount of sawing on rough wood. I was kind of surprised that more people didn't speak up about a higher dollar saw being stiffer without being harder to file (and despite having at least as much of their cross section removed for tapering). 

Some of the rest was kayfabe to some extent. 

Maybe the selection of saws is different in the UK. The bulk of the $50 clean saws here that were intended to be used on a jobsite by a professional were disston, but there were plenty of cheap saws, too (often branded by disston or some other substandard companies). 

The saws with good stiffness are just a bit nicer to use. Less rattling in the cut, fewer surprise (but harmless) binds. I'm not going to make the claim that they kink less because you have to be pretty seriously horsing a saw to kink it. 

I think the statement just before here is apt - something causes the saw to be stiffer. I would assume it's tensioning (which is a step that japanese makers still list separately from straightening). It can be noticed, by amateur or whoever else. Maybe it just takes the right kind of work to notice it. I guess if I think back to when I used saws only for crosscutting, I didn't really know what the big deal was about the better saws. If there is marketing to marks, I think it is at the very top of the range where saws had sayings put on them and were given things like rosewood handles.


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## AndyT (29 Feb 2016)

Way back on page one of this thread, I mentioned a note in an old book about saw tensioning. It was in "Woodwork Tools and How to Use Them" by William Fairham, one in a series of handbooks published by The Woodworker in the 1920s. 

It was actually about backsaws, but I think it's applicable to panel saws. It said:

"The sheet of steel which forms the saw blade is hammered so as to make it flat; it is also hammered so that the centre of the blade is slightly expanded, and always pulling at the toothed edge to keep it taut and true. The condition of the saw is, in fact, like a piece of paper as at Fig 20, the toothed edge being stretched tight and the body of the saw loose."







Sorry it's taken me a while to get round to posting this, but I've been away.


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## Sheffield Tony (29 Feb 2016)

I have to say I share the scepticism mentioned earlier in this thread as to whether a significant amount of tension can be created without the blade becoming dished, poping between bulging out one side or the other. I also wonder how much roller pressure or hammering is needed on a tempered spring steel to stretch it significantly whilst cold ? But then I'm an engineer too :wink:


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## D_W (29 Feb 2016)

As for the rollers, I think the engineering term would be "many elephants of pressure". 

It would be interesting if someone could come up with a picture of the rollers at disston. I'm sure they don't look like skateboard wheels. Even if they had 50 tons of pressure on them each, or more, it would've been trivial for disston to make something like that given the size of their operation.


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## D_W (29 Feb 2016)

As to the odds of the tension being a real difference (it's possible that my generics were just dogs, and not necessarily lacking tension, but just bad saws - that are floppy because they're lacking ____...I don't know what). 

These saws were sold to people in an era where there wasn't a lot of disposable income, in an era when labor was probably fairly cheap compared to tools and equipment, and they were sold in droves at an extra cost. I know how my relatives (who were farmers) lived back then, and they didn't spend extra money on much. 

There probably wasn't a bloated tax rate to write off equipment against, either. It sort of reminds me of the double iron discussion - cost a lot of extra money to get one put in a plane, but there are still people who call them a con on the craftsman.


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## Corneel (29 Feb 2016)

The pressure of a hammer can be very high too, because the area of the impact is small. When you can straighten a saw with a hammer, it should be possible to do the "tensioning" with a hammer too.


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## worn thumbs (29 Feb 2016)

AndyT":3dy1014w said:


> Way back on page one of this thread, I mentioned a note in an old book about saw tensioning. It was in "Woodwork Tools and How to Use Them" by William Fairham, one in a series of handbooks published by The Woodworker in the 1920s.
> 
> It was actually about backsaws, but I think it's applicable to panel saws. It said:
> 
> ...



Excellent post and it reminds me of the tenon saw I found in a box of old tools I bought at auction in the eighties.It hadn't been of interest but when I had sorted the other items and sold on those I had no use for it languished at the back of the workshop for a while.Finally I picked it up with a view to either binning it or making it usable.After a good scuff with wire wool and WD-40 there were bulges apparent and the whole saw felt floppy.Since I had a block of steel and a hammer (most of us own hammers,don't we?) I had nothing to lose but the time and I spent an hour or so making things less bad.It worked and I was able to set and sharpen the saw.It was even good enough that a good few years later I sold the saw to a carpenter for twice the price I paid for the box of old tools.Could I do it again?Probably and eventually,but it demonstrated to me that tensioning with a hammer works.I think we have arrived at a point where the general principle has come to the surface,even if it seems counter-intuitive.


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## Sheffield Tony (29 Feb 2016)

Well yes, but people also were impressed by "Electro Boracic steel" (whatever that meant) and corrugated plane soles. I've no doubt various processes were done, and were either thought to, or claimed to, improve the tool. Whether it actually made a difference is harder to tell !

(sorry, got out of sync there - this was in response to D_W's comment that people would pay more for the higher quality "tensioned" saws)


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## D_W (29 Feb 2016)

Corneel":rqqyx6om said:


> The pressure of a hammer can be very high too, because the area of the impact is small. When you can straighten a saw with a hammer, it should be possible to do the "tensioning" with a hammer too.



Definitely. Just less uniformity in results, maybe. It wouldn't take a very large hammer to distort the metal, it doesn't take much to straighten a saw and leave visible burnish marks.


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## D_W (29 Feb 2016)

electro boracic must've been an alternative to carbo magnetic.


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## Bedrock (1 Mar 2016)

As a non-engineer, I can at least understand how this tension might be applied to a back saw, because the back gives the blade something to brace against, but am I right in deducing that this would have to be done once the blade is firmly fixed into the back?

I don't see how the tension is introduced into a handsaw where there is nothing to hold the top edge against the tension, unlike a bow or coping saw.
Can someone please enlighten me?
I have 4 handsaws, 2 old Disstons, one a D8, and 2 S&Js, one of each rip and the others cross cut. Of any of them, one of the S&Js cross cut, is noticeably more flexible then the others. It's a nice saw to use, but if my hand is not relaxed, rattles in the cut. Does a more flexible blade necessarily indicate a better quality saw, and thus is it more likely to have been "tensioned", however applicable that might be to a hand saw?
I doubt that any of the throwaway hard points so prevalent today, are tensioned in anyway, but seem to perform reasonably well. That being the case, what benefit might any reasonably competent workman notice from such a saw being tensioned?


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## D_W (1 Mar 2016)

Bedrock":1eyjm9rv said:


> As a non-engineer, I can at least understand how this tension might be applied to a back saw, because the back gives the blade something to brace against, but am I right in deducing that this would have to be done once the blade is firmly fixed into the back?
> 
> I don't see how the tension is introduced into a handsaw where there is nothing to hold the top edge against the tension, unlike a bow or coping saw.
> Can someone please enlighten me?
> ...



Other way around...the stiff saws are tensioned and the stiffness makes them preferable.

Less rattle, flop, bind, etc are the reason that stiffness is preferable. 

The heavier you use the saws, the more you notice the difference.


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## Cheshirechappie (1 Mar 2016)

Stiffness is down to the material's dimensions, not any change in it's mechanical properties. It's proportional to the cube of the length, and it's also proportional to the cube of the thickness. Consequently, quite a small increase in a saw blade's thickness gives a noticeable increase in stiffness.

Just to develop this a bit, consider a handsaw or panel saw, clamped to the bench at the handle end, with the blade poking out flat across the workshop. Now, take a loop of string, and put it round the blade a given distance from the handle. Hang a weight on it, and measure the deflection. Now take another saw, identical except in thickness, and do the same. You'll find that the thicker saw has a significantly reduced deflection.

In engineer speak, we'd analyse this as a cantilever fixed at one end. The beam formula for deflection is (weight applied times length cubed) divided by (3 times modulus of elasticity of the material times moment of inertia). The moment of inertia of a simple rectangular section is (breadth times depth cubed) divided by 3.

Thus, the deflection caused by a given force applied (the weight) is proportional to the cube of the length, and the cube of the thickness. The material property quoted, modulus of elasticity, is pretty much constant for steel under any condition of temper, hardness or whatever (it varies very slightly with temperature, but unless you get up to a couple of hundred centigrade or so, the variation is insignificant).

More practically, if anybody cares to measure the thickness of their blades with a micrometer, they'll find that the stiffer ones are the thicker. It's a tad more complicated with hand and panel saws because of taper grinding, but in general the thickness of metal for the inch or two behind the tooth line will pretty much define the saw's stiffness. An increase in thickness from 0.030" to 0.036" will increase stiffness by a factor of 1.73.

Sorry that's all a bit technical, but it's needed to explain why stiffness is related to thickness, not to the steel's metallurgical properties or internal stresses.


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## Cheshirechappie (1 Mar 2016)

I think I may have an idea what 'tension' is on saw blades.

Back on page 2 of this thread, Worn Thumbs mentioned shot peening. If you look this up in Wikipedia - https://en.wikipedia.org/wiki/Shot_peening - and scroll down to 'History and further developments', you'll find the interesting fact that shot peening was invented in the late 1920s because somebody noticed that blacksmiths peened the tension side of leaf springs with a ball-pein hammer to increase their life. The blacksmiths didn't know why peening springs increased their life, they just knew it worked.

We do know, now. It's to do with the internal stresses in the metal, sometimes called residual stresses. Residual stresses have been known about for a long time (or perhaps more accurately, their effects have), but even now they're not particularly well understood. Wikipedia again - https://en.wikipedia.org/wiki/Residual_stress .

As far as the springs were concerned, the peening worked because it caused a compressive residual stress in the surface of the metal. That was beneficial because when the spring was loaded, and tensile stress built up in it, the stress had to cancel out the residual compression, and only then start building tension. Thus, the spring could bear a bit more load before failing. Another advantage is that cracks, which start easily in components under tension do not in components in compression (which way do you nick and bend a stick to break it?).

It's not hard to surmise that in a place that works steels a lot, somebody making springs would mention to somebody making saws (from the same steel) that a good peening would make saws last longer, because it works for springs.

Thus, I suspect that inducing a residual compressive stress in the surface of a saw blade makes it less prone to cracking since cracks don't start in compressed material. Why call it 'tension' then? Well, I don't know, but perhaps because the idea came from spring-making?

A residual compressive stress can be induced in the surface of a metal by hammer-peening it, by shot-peening it, or by rolling it. Modern spring-steel comes from the mill with a cold-rolled finish (they call it 'temper rolled', which is rather confusing) to give it a good surface finish (the bulk of the reduction from cast ingot is done hot). That will effectively give modern saw makers pre-'tensioned' material to work with. The old makers, who hot-rolled their steel from the ingot, then shaped and toothed the soft steel, then heat-treated, had to 'tension' as a separate operation, either by hammering or rolling.

Well, that's not proof positive, but I offer it as a working hypothesis. It seems to fit the historical facts as far as we know them, and it fits with modern materials science knowledge. 

Thoughts?


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## D_W (1 Mar 2016)

Cheshirechappie":21z2lie1 said:


> More practically, if anybody cares to measure the thickness of their blades with a micrometer, they'll find that the stiffer ones are the thicker.



So, you've concluded now that there's no such thing as tensioning without actually proving it. 

I mentioned earlier that I measured my saw plates for taper and tension (I measured them with calipers at the front top, front bottom, back top and back bottom to get an idea of how they were ground. I did that long ago out of curiosity, though. The floppy saw that I'm comparing to a good rip saw was just as thick as a disston D8, and it was tempered only in one direction (there was more steel left in it). 

Nearly every rip saw is about 4 hundredths or slightly more at the tooth line, and the small panel saws are about a hundredth thinner. They vary a lot at the front and top, depending on how much they were ground. The saws with more steel remaining aren't any less stiff in use (they're more stiff, actually, but not because of thickness).

I think you should do a little bit more homework and actual hands on use before you make a definitive conclusion. I guess you wanted to come to this thread and authoritatively state that saw tensioning has no effect and you've ignored everything since then. =D>


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## Cheshirechappie (1 Mar 2016)

Oh well, can't please all of the people all of the time.

On stiffening hardened and tempered high carbon (spring) steel by hammering, or rolling, or shot-peening it, I stand by what I wrote. It just doesn't happen. Stiffer saws are thicker saws, and as described, it doesn't have to be much thicker to be appreciably stiffer.

You say I wanted to come to this thread and authoritatively state something. Well, I didn't, and I haven't. Virtually from the off, I've said I'm open-minded but sceptical about 'tensioning'. I now have a hypothesis about what tensioning is (so I'm not saying it doesn't exist), but I do state categorically, as I have for some pages, that it isn't some way of stiffening steel by hammering it. I think it's more a way of making saws less liable to crack and break - extend their fatigue life, in technical terms.

The idea occurred whilst I was lying in bed on Saturday night. I was (not intentionally - the mind was just doing it's own thing, as they sometimes do) mulling over the shot-peening Wikipedia reference, and remembered a passage from "The Village Carpenter" by Walter Rose. It's on pages 59 and 60 - "The saw, eventually purchased, was of marvellous quality, a delight to use. But I took it to work on a new house, it was borrowed by the labourers for cutting firewood, and on my return I found it in my basket broken in two." I've never broken a saw, and I don't know of any other instances either.

If they're so hard to break these days, why is it? Maybe because the compressive stress in the surfaces makes crack formation very hard - the same compressive stress that the old blacksmiths used to peen into their springs, and that results from cold rolling or shot peening. Maybe that's why (and how) saws were 'tensioned'.

I've spent those odd moments when I haven't been doing things I ought to be doing since then trying to pick holes in the idea, but I can't. It just fits the known data. That doesn't mean proof, but it does mean it's an idea worth offering as a possible explanation.


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## D_W (1 Mar 2016)

You have stated something specific. You've specifically said that you can't tension a saw by hammering or rolling it. 

So you're making the claim that it was either a sham or someone was misguided (and that includes a gaggle of engineers working at disston, and not in the stone age). 

As well as a gaggle of japanese saw makers. 

If Lloyds took bets, and you asked if you can make a saw plate stiffer by hammering or rolling it, I know which bet I'd take.

The poster who described two saws here should have an interesting opportunity at this point to take a set of simple calipers and compare the saws he was discussing as he clearly noticed a floppy saw and two stiff ones, just as I have in the past. Do I know for sure that it was tensioning that made them stiffer? No, for all I know, they could've been different hardness. 

By the way, the tensioning step isn't described as something that makes a saw more flexible and less apt to break. All decent saws can have their toe turned to their handle unless they are defective or damaged. It makes the saw stiffer and more likely to return to straight.


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## pedder (1 Mar 2016)

Wow 7 pages and nobody has looked for the hammer marks on saws.


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## Cheshirechappie (2 Mar 2016)

D_W":3r8o44kt said:


> You have stated something specific. You've specifically said that you can't tension a saw by hammering or rolling it.



That accusation is flat wrong. I have not stated that you can't 'tension' a saw by hammering or rolling it (though earlier in the thread I was pretty sceptical). I have stated - and continue to state - that you can't STIFFEN a saw by hammering or rolling. (You can, however, work harden a piece of soft metal so that it becomes springier and more elastic, but that doesn't actually make it stiffer. You can, to a much lesser degree, induce a bit more work hardening into a piece of hardened and tempered spring steel by hammering it, but again, that won't change it's stiffness.)

That leaves us trying to interpret what all the old sources meant by 'tensioning', the problem being that whilst some explicitly state that it was a process in saw manufacture (though I've yet to see one that says when this step started to be used), they're all frustratingly vague about what it was or did. Some strongly imply that it was carried out during one of the smithing operations, and involved hammering, but that's about as much as they tell us.

The suggestion that it may have been a technique borrowed from spring-making practice, using a process of peening to increase the life of springs, is just that - a suggestion. It isn't proof. However, it fits the metallurgical facts as we understand them in the 21st century, whilst the idea of stiffening a hardened and tempered saw blade by hammering does not.


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## Rhyolith (2 Mar 2016)

Andy's post has made be confident that my original hypothesis of saw tensioning in panel saws being the same as in bow saws (stretching of the blade/cutting edge) is correct. I am not at all convinced that stiffness is even relevant to saw tensioing, I think its a seperate process or at least not the principle objective of saw tensioners.

*Please answer these questions (especailly Ches.):
- Whats better a bow saw with a tensioned or un-tensioned blade?
- Is it possible, by mechanical means such as those in Andy's book, to expand to central area of the saw panel to manipulate the tension of the cutting edge in a panel saw?*


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## MIGNAL (2 Mar 2016)

If you can't reduce a difficult engineering problem to just one A4 sheet of paper you will probably never understand it.
 Page 8 and I'm still none the wiser.


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## Cheshirechappie (2 Mar 2016)

MIGNAL":3s4b2euv said:


> If you can't reduce a difficult engineering problem to just one A4 sheet of paper you will probably never understand it.
> Page 8 and I'm still none the wiser.



Sorry  probably my fault, using technical terms like 'stress' without explaining them.
materials 
Just for the sake of (some attempt at) clarity, I'll try to explain a bit about stress, as used in engineering and materials science world. It's not quite the same thing as the stress all of us encounter in everyday life; though I suppose there are parallels of a sort.

An engineer would define 'stress' as a way of measuring a material's capacity to cope with the loads applied to it, and define the point at which the material can't cope with the loads, and fails. A simple example would be a crane cable holding up a load. The cable would have a tensile stress in it, because it's in tension. The stress is defined as the load applied divided by the cross-sectional area affected by that load. So if the crane cable had a cross sectional area of 1 square inch, and the load was five tons, the stress in the cable would be 5 tons per square inch.

The load applied to the cable would tend to stretch it a little bit, and the amount by which it stretches (the extension) divided by it's original length gives another figure engineers use quite a bit - strain. Up to a point, if you divide the figure for stress by the figure for strain, you end up with a constant, called the Modulus of Elasticity (or sometimes. Young's Modulus). Note the word elasticity - that's because up to a point, many materials behave like a piece of elastic - apply a load, and they deform a bit, but take the load off again, and they return to their original shape.

However, that's only up to a point - after that point, they deform permanently. In other words, they behave plastically. That point is known as the 'yield point'. Keep on applying load, and they keep on deforming permanently - up a point. THAT point is when the material gives up and breaks - the Ultimate point.

Thus, a piece of (say) mild steel subjected to gradually increasing tension load will behave elastically up to it's yield point, then plastically up to the Ultimate Tensile Strength of that grade of steel.

Each material has it's own points for Yield and Ultimate, often quoted by material suppliers.

Just to make life more interesting, you can modify the yield and ultimate for many materials by such actions as heat treatment or cold work. A piece of spring steel in it's annealed - soft - state will have quite a low yield point, and a longish plastic range. However, harden and temper it, and it will have a very long elastic range - a high yield point - but a much shorter plastic range thereafter, but it's Ultimate will be much higher than it was when it was soft. Conversely, a blacksmith or forgemaster can heat the spring steel to a suitably high temperature when it will have a very low yield, but a very long plastic range - so he can do a lot of drastic shaping without causing the steel to fail. Also, if you take your piece of soft spring steel and cold work it (hammer it, bend it, draw it through dies or whatever) you will increase it's yield point by work-hardening it. This is very noticeable with metals like copper and brass. Once it's hard - high yield point, short plastic range - you can soften it again by annealing, thus restoring a low yield point and large plastic range.

Confused yet? You will be!

Stresses are 'tensile' if the material is being stretched, and 'compressive' if it's being squeezed. (There's also shear stress, which happens when the load applied is trying to 'shear' the material - bolts, rivets and shear pins often see a stress of this type.)

Now, let's consider our saw blade. If it's just lying on the bench, it's not subject to any stress. If it's picked up, and the toe end bent round so that the blade takes up a curve, it's effectively acting as a beam (a cantilever, in this case). Beams see both tensile and compressive stresses; if you take a piece of flat steel and bend it into a gentle curve, the outer side of the curve is now a little bit longer than it was when straight, and the inner side a little bit shorter. The outer side is thus in tension, and has a tensile stress, and the inner side in compression, and has a compressive stress. The line through the middle remains the same length, and sees no stress - that's the 'neutral axis'. Thus, our bent saw blade is in tension on the outside of the bend, and in compression on the inside, with stresses to match. 

It now gets complicated. So far, we've only considered stresses resulting from externally applied loads or forces. However, there exist another sort of stress known as 'internal stresses', or sometimes, residual stresses - https://en.wikipedia.org/wiki/Residual_stress . They have been known about for quite a long time, but even now are not well understood, perhaps because they are very difficult to measure. They can be a problem, or they can be beneficial. They tend to find an equilibrium within a piece of material, so a piece of steel - such as a sawblade - just sitting on a bench on it's own, can appear stable, and under the influence of no loads (and hence stresses) applied to it. There can, however, be stresses IN the saw blade. If any loads are then applied externally, the stresses resulting from those loads add to the internal stresses.

Most failures of relatively strong materials like spring steels tend to happen when a crack starts in part of a component under tensile stress. The crack runs quite fast, and the component breaks in two. It's much harder to start a crack in part of a component under compressive stress. Try bending a stick of wood, then putting a nick or sawcut in the tensile (stretched) side of the bend - it'll break sooner. Not so if the sawcut is in the compressed side.

Let's now imagine some way in which we could manipulate the internal stresses in the saw blade such that the surface layers were in compression (and to balance the stress distribution, the centre was in tension). When the saw lay on the bench, it would be stable, because no external forces were applied. Now let's pick up the saw and bend the blade into a curve, as before. Now, the outer side, which had a tensile stress in it as soon as the bend started, starts with compressive stress, so as the bend develops, the stress comes from compressive, back to zero, and only then starts to become tensile. Thus, the maximum tensile stress the surface sees is lower than in the saw blade with no internal stresses. Cracks start in materials with tensile stress in them; less tensile stress, less chance of cracks starting.

Way back in the mists of time, blacksmiths discovered that if they peened the tensile side of leaf springs, the springs lasted much longer. They didn't know why, they just knew it worked. It works because peening a surface (or rolling it lightly, or shot-peening it - https://en.wikipedia.org/wiki/Shot_peening ) puts a compressive internal stress in the surface. Thus, the maximum tensile stress the spring surface saw was lower than one not so peened, so cracks were less likely to start, so the spring was less likely to break.

Springs and saws are made from pretty much the same grade of steel (sometimes in the same works, in times gone by). Not hard to see that what works for springs would also apply to saws (which are just wide, flat leaf springs with teeth on one edge).

Thus, I think 'tensioning' is a process that makes sawblades less likely to snap in use, and it's done by peening the surface of the saw blades. Light rolling would work too, as would shot peening. I've no idea why it's called 'tensioning', but as the idea came from spring-making practice, maybe that has something to do with it.

Well - that's the brief :shock: explanation. I don't know if it's the full answer to the question of what 'tensioning' is, but it seems plausible from the materials science standpoint.

Right. I'm off for a rest after that!


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## Cheshirechappie (2 Mar 2016)

Rhyolith":3kz4sq8l said:


> Andy's post has made be confident that my original hypothesis of saw tensioning in panel saws being the same as in bow saws (stretching of the blade/cutting edge) is correct. I am not at all convinced that stiffness is even relevant to saw tensioing, I think its a seperate process or at least not the principle objective of saw tensioners.
> 
> *Please answer these questions (especailly Ches.):
> - Whats better a bow saw with a tensioned or un-tensioned blade?
> - Is it possible, by mechanical means such as those in Andy's book, to expand to central area of the saw panel to manipulate the tension of the cutting edge in a panel saw?*



The bow saw blade is placed under an external tension, so the 'tension' in the blade is only there if it's stretched in the bow-saw frame. It's not there if the blade is just lying freely on the bench - or if the blade is used without the frame. Handsaws and panel saws are used without any frame stretching them.

If the middle of a hand or panel saw blade is hammered to the point where the metal yields (see previous post - I'm not typing that lot again!), but the metal either side of it is not hammered, you get a bulge developing in the blade. That bulge can be removed by stretching the metal above and below it - the old saw smiths used to do that to get blades cockled in heat treatment flat again.


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## MIGNAL (2 Mar 2016)

Thanks CC. Much clearer. Now can you explain why Building 7 came down at free fall speed?


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## Cheshirechappie (2 Mar 2016)

MIGNAL":16uthlux said:


> Now can you explain why Building 7 came down at free fall speed?



Not tonight. I've got a blister on the end of my typing finger!


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## Rhyolith (3 Mar 2016)

Cheshirechappie":fr57oynd said:


> Rhyolith":fr57oynd said:
> 
> 
> > Andy's post has made be confident that my original hypothesis of saw tensioning in panel saws being the same as in bow saws (stretching of the blade/cutting edge) is correct. I am not at all convinced that stiffness is even relevant to saw tensioing, I think its a seperate process or at least not the principle objective of saw tensioners.
> ...


Well I am not convinced. What you merely makes me think its hard to do rather than impossible.

Unless more evidence comes to light, I think expanding the central area of the saw and thus streatching the blade is what tensioning is. If this is what it is then it will make a difference, as evidenced by bow saws.


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## AndyT (3 Mar 2016)

As an aside, to anyone who's followed CC's essays in this thread, and thinks they would like to get a more scientific understanding of concepts such as stress, strain, elasticity, stiffness, cracking, malleability etc I would recommend a couple of books. 

Both by JE Gordon, published by Penguin/Pelican, they are Structures, or Why Things Don't Fall Down, and The New Science of Strong Materials or Why You Don't Fall through the Floor.

Probably in your local library (the links can help you find them) or pennies secondhand. 

They cover the fields mentioned and a bit more, illustrated with everyday examples. I find that while I am reading them, they make perfect sense - but I admit that I struggle to reproduce the explanations as clearly as CC has done.


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## ED65 (3 Mar 2016)

Cheshirechappie":2utxtkab said:


> I have stated - and continue to state - that you can't STIFFEN a saw by hammering or rolling. (You can, however, work harden a piece of soft metal so that it becomes springier and more elastic, but that doesn't actually make it stiffer. You can, to a much lesser degree, induce a bit more work hardening into a piece of hardened and tempered spring steel by hammering it, but again, that won't change it's stiffness.)


Hang on a sec, isn't harder metal stiffer by definition? I hope this isn't one of those things where the engineering understanding of the word is utterly at odds with how a layman would use it [-o< but I've experienced firsthand that work-hardened steel can bend less easily than the same steel in a fully annealed state, surely that does mean it is stiffer?


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## D_W (3 Mar 2016)

Harder steel (of the same alloy) is stiffer, yes.


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## D_W (3 Mar 2016)

Rhyolith":3rsj2i1f said:


> Cheshirechappie":3rsj2i1f said:
> 
> 
> > Rhyolith":3rsj2i1f said:
> ...



Here's what disston said about saws that were "loose" (hard would be a good term, meaning a layman is not likely to chance into - say - finding some guy to just hammer around on a saw and then make a conclusion that you cant increase stiffness by manipulating the metal). 

http://www.disstonianinstitute.com/factorytour.html (halfway down - this all occurs after a blade has been hardened, tempered and ground - as we were told earlier in this thread, all of this stuff is unnecessary)

_The next step is that of "Smithing." in this the blades are flattened and made perfectly straight, all inequalities being taken out by the skillful hammering of the mechanics.

The blades are next "Ground" to gauge and to a taper so that the back will be thinner than the cutting edge. The back of the hand saw blade is ground to taper from the teeth to the back and from handle to point, the tooth-edge being of even thickness from end to end. A saw not ground to proper taper cannot be ranked as a high-class tool.

Taper Grinding

Grinding
After being ground they are returned to the smithers for "Looking-over" and preparing for next operation.

Now follows "Tensioning." In this the blades are hammered so that they shall not be too "fast" or too "loose;'' but shall possess the proper tension, spring or character. If the blade is what is termed "fast" the metal is too long on the edge and needs expanding through the centre, or, if too "loose" the metal must be stretched on the edge. A saw not properly tensioned will run out of its course, in other words it will not cut straight and true._


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## Rhyolith (3 Mar 2016)

Thats still quite vague. Even though it supports my thoughts on what tensioning is, its not enough to "prove" anything definitively.


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## D_W (3 Mar 2016)

Rhyolith":1fz0dzxq said:


> Thats still quite vague. Even though it supports my thoughts on what tensioning is, its not enough to "prove" anything definitively.



No, proof only comes in a craftsman's sense sort of way. That is, until someone has enough skill to actually duplicate what Disston is talking about, we are left to guess one of two ways:
1) the above process either does nothing at all or it doesn't stiffen the tooth line (it's clear that disston doesn't think that tensioning is intended to make the saw more flexible or keep the steel from failing - that is taken care of long before)
2) that the process does something, and then decide what we think it is. Certainly the tensioning is described in some places as ensuring that the saw will return to straight, and in this case, it has to do with tracking. A stiff saw tracks better. If someone doesn't believe that, try making a very tall backsaw with a thin plate. See what happens. 

I'm satisfied to prefer the stiffer saws. How they got that way without seeming harder under the file, and while having more of their plate ground off is, apparently, not going to be explained.

I thought at one point I'd like to hammer a floppy saw to see if I could tension it, but I don't know if I have a candidate in my shop or not (I have one or two, but I might rather sell them and get some money for them rather than beating them into valuelessness). At this point, after reading about it, I'm thinking that my odds of actually stiffening a saw as an inexperienced amateur - they're pretty low.

Just because I have not much confidence in my ability, or the modern boutique saw makers' ability to tension a saw as disston describes doesn't mean I think they couldn't do it.


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## Cheshirechappie (4 Mar 2016)

D_W":2wod5reb said:


> Here's what disston said about saws that were "loose" (hard would be a good term, meaning a layman is not likely to chance into - say - finding some guy to just hammer around on a saw and then make a conclusion that you cant increase stiffness by manipulating the metal).



*sigh*

I've spent 8 pages saying that you can't make a piece of hardened and tempered spring steel stiffer by hammering it. How much more often will I have to state that before it finally sinks in?

Whatever 'tensioning' is (see rest of thread for discussion) it isn't a way of stiffening saw blades. If you want a stiffer saw, make it from slightly thicker material.


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## pedder (4 Mar 2016)

Still discussing? Why not look for the hammer marks. Or try. 
Prove it. This can't be dissolved with words.


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## CStanford (4 Mar 2016)

Chappie, unless you are a metallurgical engineer (are you?) why should we accept what you say any more than you accept what we say or by extension the links that have been posted?

I'm an accountant by professional training. That doesn't mean I could walk into General Electric tomorrow and take over their general ledger accounting for derivatives, special purpose entities, and/or foreign subsidiaries who use different bases of accounting.

If I recall, David W. is a licensed actuary. I'm certain that he has a broad range of expertise in many areas but surely there are some parts of the profession he would initially be uncomfortable dealing with. Aren't all professions like this? Why is yours any different? Would one hire a bridge engineer to design biomedical devices?

You've assumed, perhaps erroneously, that you are somehow the most qualified participant in the thread. I'd rethink that.


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## Rhyolith (4 Mar 2016)

I have been emailing tool companies to try and get some more information to work with, this is a semi-useful response from Lie-Nielsen.


Lie-Nielsen":1dhmnokg said:


> “The Disston Saw co was the first maker of what is called Crucible Steel here in the US. They were very secretive about the process that they used to prepare the steel for their saws, and they also were very tightlipped about the process they used for tensioning their saw plates. They did hammer tension the saws, but there is no documentation of what that actually meant. It is far more likely that it was the formula used for the steel and the heat treating process for that steel that gave their saws tension, than that it was the hammering itself. I could be wrong, but I have talked to other makers as well and none of them have been able to get provable results from hammer tensioning. You can hammer out a bow or a kink, but it does not seem to increase or decrease the stiffness or “tension” in the saw.
> This was either a form of misdirection on their part or a technique that has been lost to time. I wish that I had a better answer for you, but it is definitely not an old wives tail. Hammer Tensioning was done, it just may not have been done to give the results that we think.”


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## CStanford (4 Mar 2016)

One would have to believe they beat saws with a hammer just for the hell of it, or as previously mentioned it was a marketing ruse practiced by every major saw making firm of the era we're discussing.


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## Cheshirechappie (4 Mar 2016)

CStanford":1sabvvex said:


> Chappie, unless you are a metallurgical engineer (are you?) why should we accept what you say any more than you accept what we say or by extension the links that have been posted?
> 
> I'm an accountant by professional training. That doesn't mean I could walk into General Electric tomorrow and take over their general ledger accounting for derivatives, special purpose entities, and/or foreign subsidiaries who use different bases of accounting.
> 
> ...



Charles, I hold a degree in Mechanical Engineering. That involved the study of, among other subjects, Strength of Materials and Metallurgy. I am currently a Corporate Member of the Institution of Mechanical Engineers, and a Chartered Engineer. My professional responsibilities have included, among other things, twelve years of responsibility for the analysis of stress in complex specialist chemical plants, mostly pipework and it's supports, but also on occasion pressure vessels and various ancillary bits and bats. That included ensuring that they new designs were safe for all operating and fault conditions for the design lifetime of the plant, and ensuring that it cope with possible events such as extreme wind, heavy snow load (in the UK? Ha!) and earthquakes (that one was quite interesting), so I do know a bit about stress. In a voluntary capacity (one day a week, basically), I have 25 years of rebuilding and operating full size steam locomotives, which includes a lot of hands-on manipulation of castings, forgings, plate, bar-stock and sheet metal.

So all in all, yes - I do feel that I have some qualification to comment on the stresses in metals, and on their manipulation. Whether I'm the most qualified person commenting on this thread I don't know, but I do feel that I have some relevant specialist knowledge to contribute.


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## Cheshirechappie (4 Mar 2016)

Rhyolith":22w7wfhf said:


> I have been emailing tool companies to try and get some more information to work with, this is a semi-useful response from Lie-Nielsen.
> 
> 
> Lie-Nielsen":22w7wfhf said:
> ...



Thanks for posting that, Rhyolith. It's interesting that other people, independent of the discussion on this thread, haven't been able to pin down what 'tensioning' is, either. It's also interesting that Disston's writer was 'secretive' about it - possibly because he didn't really know either.


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## D_W (4 Mar 2016)

pedder":2x78hwzi said:


> Still discussing? Why not look for the hammer marks. Or try.
> Prove it. This can't be dissolved with words.



If the boutique sawmakers haven't been able to figure it out, what chances do we have just beating around saws?

We're not likely to find many saws with hammer marks on them, most of us have saws that were made when straightening was done with rollers, or at the very least, a light dressing of the metal was made after the saw was finished so as to have a bright and uniform plate. 

If we go back to when saws would've been tensioned by hand, we don't have any good reason to believe the saws haven't been hammered between then and now, especially since they likely wouldn't have been tensioned as well as a later saw and would probably need to be straightened with a hammer at some point. 

What we would like to have is someone comparing saws of similar hardness (where one is known as a second or third line saw, and another - or ten - first line - all from the same maker), and where the tensioned saw has less metal in its cross section, and see if we can find that the better quality saws deflect less under a given weight. 

Or we can just use them and know they're stiffer and more likely to remain straight in a cut (that part is pretty easy to notice if someone wants to actually go to the trouble of using a saw for more than cutting off 2x4s)


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## D_W (4 Mar 2016)

Cheshirechappie":pfth96uq said:


> Thanks for posting that, Rhyolith. It's interesting that other people, independent of the discussion on this thread, haven't been able to pin down what 'tensioning' is, either. It's also interesting that Disston's writer was 'secretive' about it - possibly because he didn't really know either.



That's beyond naive. You're talking about print that was made at a time when saw makers were intensely competitive with each other. They're not going to create a 12 step process, show and describe everything so that someone else can just do it, too. 

Plus, you assume that just because you and I don't know what a fast or loose saw is, that nobody would've known what it was in 1900 - also very naive. For all we know, it may have been a common term back then.


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## Cheshirechappie (4 Mar 2016)

D_W":3s3zbbop said:


> Cheshirechappie":3s3zbbop said:
> 
> 
> > Thanks for posting that, Rhyolith. It's interesting that other people, independent of the discussion on this thread, haven't been able to pin down what 'tensioning' is, either. It's also interesting that Disston's writer was 'secretive' about it - possibly because he didn't really know either.
> ...



The terms 'fast' and 'loose' are described quite fully - at least, I understand what they mean ('fast' means wavy at the edges but straight and flat down the middle, 'loose' means straight and flat down the edges, but bulging in the middle, both conditions can be cured by stretching the straight bit, thus pulling the wavy bits straight). It's the term 'tensioning' that's frustratingly vague.


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## pedder (4 Mar 2016)

One the one hand all I have is the writing of a PR manager of a industry corporate group. On the other hand, every engineer, I've spoken to, think it is completly nonsense. 

Oh yes and proofs can't be found today, because, they changed the way.

So nobody can describe the procces, no proofs can be found and it can't be done by one of us....

Get a hammer and a floppy saw and try your luck it can make you rich. :lol: 

Cheers
Pedder


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## CStanford (4 Mar 2016)

Bob Smalser, in the link already posted, states:

"When a thin blade is struck on an anvil by a convex-faced round hammer, a dimple is created; often so small it can’t be seen by the eye. Steel from the area around the dimple is pulled inwards toward the point of impact, making the steel in the circular area radiating from the dimple stiffer, or “tensioned” on its surface."

If this statement is true, metallurgically, then it would seem that we have our answer. A lot of these little dimples would add up to a saw that had been 'tensioned.'

He goes on to say:

"Hundreds of such hammer blows applied in certain patterns equally to both sides of a handsaw blade can make it stiffer, can true a warped circular sawblade, or can dish a large bandsaw blade to conform to its wheels while at the same time tensioning the cutting edge."


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## MIGNAL (4 Mar 2016)

Should be easy to prove then, just with the use of a hammer, an anvil and a bit of saw plate.


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## CStanford (4 Mar 2016)

http://sro.sussex.ac.uk/43235/

http://www.scientific.net/KEM.410-411.449

https://www.google.com/search?q=sheet+m ... 3IhAAcM%3A

https://www.google.com/search?q=sheet+m ... CTxW-bM%3A

"The UltraSTEELTM process, developed by Hadley Industries Plc (Hadleys), is a novel surface dimpling process used on steel strip prior to cold roll forming. This dimpling process increases the strength of the final rolled products and enhances other product properties such as fire test performance and screw retention."

C. J. Wang, D. J. Mynors, M. English, "Simulating the UltraSTEELTM Surface Dimpling Process", Key Engineering Materials, Vols. 410-411, pp. 449-456, 2009


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## Rhyolith (4 Mar 2016)

I think there is yet another divide here: What Disston meant by "saw tensioning" and a number of other techniques that can justifiably be called "saw tensioning". It seems increasingly that whatever Disston did will remain a mystery, which is a shame really.


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## MIGNAL (4 Mar 2016)

Was this 'tensioning' exclusive to Disston?


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## CStanford (5 Mar 2016)

It wasn't confined to Disston.

See my link earlier in the thread to S&J's 'Story of the Saw.' Spear and Jackson were tensioning their Spearior line by hand hammering AT LEAST as late as the early 1960s, the date of the publication.

They used the same term, tensioning, in the publication and also mentioned that it was done by 'highly skilled smiths.'


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## Rhyolith (10 Mar 2016)

Got a reply from Spear and Jackson concerning Saw tensioning.


Spear & Jackson":24jcxuqf said:


> In the early days when materials were supplied in the normalised state, craftsmen would roll tension and hammer the blade to induce spring back and tension.
> Below is an extract from an old Woodsaw journal that mentions tension.
> 
> 
> ...


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## Rhyolith (10 Mar 2016)

And more from Lie-Neilsen following more queations, not sure there is anything new here. 


Lie-Neilsen":q1s0q3vq said:


> I believe all of their saws were hammer tensioned. It seems most likely though that it is the steel itself that made for a nice stiff saw plate. There is no one today that makes steel the way that Disston did, so even though modern steels may be more consistent, the results are not the same. Since that formula and how the steel was treated was a carefully guarded secret, it may not be possible to recreate what they did today. We can analyze old blades and get steel made to the same specs, but no one knows what they did to it after that. Like many things from the past, those oldtimers may have taken the secrets to their graves.
> 
> None of our saws are “Hammer tensioned”, but the backsaws are tensioned after they are fitted to the back. All of our Panel Saws are also taper ground, which only a couple of other makers are doing today.



And a little more on the apparent tensioning of Lie-Neilsen's brass back saws... I have asked for more info on this. 


Lie-Neilsen":q1s0q3vq said:


> We slit the brass backs to receive the saw plates, then rather than just relying on friction and adhesive to hold them in place, we compress the brass back onto the plate, which also increases the tension in the plate.


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## D_W (10 Mar 2016)

I'd be curious to know how they've concluded that it's the treatment of the steel (presumably by temperature, and not by rollers) that they think has stiffened the saw. Of course, everyone's allowed a guess or five. 

I say that because there's no way they heat treat their own saw steel.


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## Corneel (8 Apr 2016)

A liitle late reply, but I found an scientific article about saw tensioning in circular saw blades and bandsaw blades. If you have access to Springer you can read it here: http://download.springer.com/static...ad4970bed7f4a74c3178ab1b3ef78fc6fb4f4300c4dfc 

A short paragraph about hammer tensioning:

The traditional way of tensioning both circular and band saws is by hammering their surfaces. The hammer blows in- dent the saw steel and squeeze it laterally in the plane of the plate. These highly localized deformations induce the tensioning stresses. Harmmer tensioning is very much an art, and great skill and experience is required to achieve good results. When done well, hammering can be as effective as more modern methods. However, hammer tensioning is usually not recommended for general use because the results can be very variable. Also, the hammer blows make the saw blade surface uneven and can initiate fatigue cracks.


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## CStanford (8 Apr 2016)

The firm Spear and Jackson were doing this at least as late as the 1960s, maybe later. Perhaps they were delusional. I tend to think not.


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## Corneel (9 Apr 2016)

The article I linked to above has something like 50 references. There is not a shadow of doubt by the authors that saw plate tensioning is a real thing, and can be explained perfectly well in scientific terms.


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## Rhyolith (9 Apr 2016)

Corneel":3ey94rs4 said:


> The article I linked to above has something like 50 references. There is not a shadow of doubt by the authors that saw plate tensioning is a real thing, and can be explained perfectly well in scientific terms.


Is it soley circular saws though? There is some debate to whether tension those and panel saws is the same thing. There seems plentiful info on circular saws but not panel saws.


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## Corneel (9 Apr 2016)

The article is about circulair and bandsaws. There is absolutely nothing about normal handsaws, nobody wants to research those and put a lot of money into it.

But I think bandsaws can be compared one way or another to handsaws. Of course, the speed is about 10 times faster.

The whole idea of and the art of tensions saws comes from the handsaw world. It was done long before mechanised sawing.


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## woodbrains (10 Apr 2016)

Hello,

I only took an interest in this thread when Corneel added a post yesterday, and just read the whole thing. I'm not an engineer, but have always believed the old texts stating that saw blades were tensioned by hammering. I did not know any better, so assumed (automatically) that the info must have come from some real world processes from saw makers. It seems a bit of an unlikely thing to be a fictitious phenomena, stated in so many published texts. Then I read the engineers here who say it is not possible to make a plate stiffer without increasing thickness! Surely this can only be true if all remains the same. Doesn't tempering, case hardening, annealing etc. vary stiffness without grossly changing thickness? Wouldn't stress hardening from hammering alter stiffness? I understand differential cooling of die cast magnesium alloy (for example) introduces tension in the structure, enabling thinner sections to be manufactured for the same stiffness. I spoke to a chap from Vauxhall motors a few weeks ago who mentioned that some car bodies are being made from thinner plate to reduce weight, but being stiffened to compensate--during the baking process involved when curing the paint finish! (I find that idea wonderful, modern manufacturing is truly sophisticated) So in my mind, it is clearly possible to make metals stiffer without increasing thickness. 

Mike.


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## Cheshirechappie (10 Apr 2016)

woodbrains":1fa69c8r said:


> Doesn't tempering, case hardening, annealing etc. vary stiffness without grossly changing thickness? Wouldn't stress hardening from hammering alter stiffness?



No.

Doesn't say much for Vauxhall cars if they make the bodywork stiffer by painting it, does it?


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## D_W (10 Apr 2016)

Painting and metal deformation are the same thing?


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## woodbrains (10 Apr 2016)

Cheshirechappie":1bpbudte said:


> woodbrains":1bpbudte said:
> 
> 
> > Doesn't tempering, case hardening, annealing etc. vary stiffness without grossly changing thickness? Wouldn't stress hardening from hammering alter stiffness?
> ...



Hello,

When I was a schoolboy, our metalwork teacher persuaded the weediest lad in class to bend a bit of thin steel plate, whilst holding it, arms straight above his head. After flattening it out, he got the butchest lad to try the same, knowing he would fail miserably. This was to demonstrate stress hardening. Has stress hardening become a myth?

Mike.


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## Cheshirechappie (10 Apr 2016)

woodbrains":u50rear1 said:


> Cheshirechappie":u50rear1 said:
> 
> 
> > woodbrains":u50rear1 said:
> ...



No. But it does not make metals stiffer, it pushes the yield point up the stress-strain curve, making them (in effect) more elastic and capable of standing higher strains before permanent deformation occurs -as it happens, exactly the qualities you want in a handsaw blade. See previous essay a couple of pages ago (I'm not typing that lot again!) for details.


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## woodbrains (10 Apr 2016)

Cheshirechappie":2mmp7nie said:


> No. But it does not make metals stiffer, it pushes the yield point up the stress-strain curve, making them (in effect) more elastic and capable of standing higher strains before permanent deformation occurs -as it happens, exactly the qualities you want in a handsaw blade. See previous essay a couple of pages ago (I'm not typing that lot again!) for details.




Hello,

If that is not a definition of stiffer, I don't know what is!

Mike.


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## Corneel (10 Apr 2016)

I had some trouble understanding that one too at first! Let me try to explain:

Take two strips of steel, same steel, one hardened, the other not hardened. Clamp them on one side to your bench and hang weights on the other end. 

You will see, until one of the blades reaches its yield point, they behave exactly the same. So they are just as stiff until the unhardened one starts to permanently deform. They are equally stiff until that point.

The article I posted above described how they increase the stiffness of a plate by putting tension into it. In circular saws and bandsaws this is important to reduce vibrations so the blade can run at higher speed. They describe several methods.
- Hammering. The hammer compresses the steel in a small area which puts the metal around it in tension.
- Rolling. The same but in a manner that asks for less skill from the operator.
- Heating spots up to +/- 400 degrees. While cooling again this causes deformations which act the same as the hammering process.
- Heating during operation. With induction coils, usually near the hub of a circular saw blade, they heat it up to 80 degrees. This creates enough tension in the blade to change its behaviour under speed. It seems this works with temperatures down to 30 degrees!.

Why doesn't the plate deform into a rollercoaster under all that hammering? That's the skill of the operator to keep any deformation so small and well balanced between the various dents that it doesn't effect the plates straightness as a whole.


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## CStanford (10 Apr 2016)

I posted several links in a post on page 10 of this thread dealing with the dimpling process of steel. It changes it. Apparently, for the better if well done.


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## woodbrains (10 Apr 2016)

Corneel":slv7w05k said:


> I had some trouble understanding that one too at first! Let me try to explain:
> 
> Take two strips of steel, same steel, one hardened, the other not hardened. Clamp them on one side to your bench and hang weights on the other end.
> 
> ...



Hello,

You are saying, if I interpret it correctly, the hammering or rolling or whatever, causes the plate to be differentially hardened. Now if there is no difference in stiffness until the less hard part reaches its yield point, and we never reach that point as it would ruin the saw plate, then there is no benefit to the process at all, apart from straightening any defects during manufacturing. Clearly there must be something else going on. Do we run saws close to the yield point of the less hard steel and the harder steel prevents the yield occurring? Distortion through heat buildup is prevented by the tensioned portion of the plate, so the tensioning process is beneficial to circular saws. This heat cannot be what we would term HOT though, surely the steel dissipates the heat fairly quickly. I guess a few degrees is enough to cause thermal expansion in the metal and cause vibrations in an untensioned plate. So I would assume that handsaws could get warm enough at the toothlike to cause similar unwanted distortions without getting hot enough to draw temper for instance. So it would be beneficial to tension the handsaw plate with hammering/rolling for the same reasons as the circular saw plate. Whatever words we choose to use to define stiff (incorrectly maybe) there is something happening to the saw plate that is hammered to one that is not, that provides some benefit.

I would add, the grain structure of hardened steel is different to unhardened, so we can never truly compare like for like in the side by side tests such as Corneel suggests. Hardened steel has a smaller grain structure and I don't see why this could not be stiffer to a similarly dimensioned unhardened steel. Stress hardening changes the grain structure. In fact hasn't the stress hardened steel essentially become a different material? This would explain quite a lot.

Mike.


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## Corneel (10 Apr 2016)

Not really (I think). I'm far from an expert in this field, just trying to tell what that article from 1984 was all about.

In my previous message there are two different things, thirst why hardened and unhardened steel have the same stiffness. Well until the unhardened gets deformed of course which happens at a rather small load allready.

The second part is me trying to explain how you can increase the stiffness of a hardened plate of spring steel (a saw). A local deformation, more precisely a compressed spot of steel, causes tension in the surrounding steel. Chappy tried to convince us with a theory that that is impossible. But there seems to be a group of scientists who have studied this back in the 70's and 80's and came up with a plausible explanation. But you really should read the article. I gave a link on the previous page. There is also a whole list of references in that article, which really is not much more then a literature study.

I you can't access the full text, I'll see if I can copy it next week when I am at work again.


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## Corneel (10 Apr 2016)

Allen, F.E. 1972: The merits of the high strain bandmill. Forest Ind. Rev. 4:9–15
Allen, F. E.; Porter, A. W. 1975: Automatic roll tensioning method and apparatus. U. S. Patent No. 3919900
Aoyama, T. 1970 a: Tensioning of band saw blade by rolls. Part I. (In Japanese) J. Japan Wood Res. Soc. 16:370–375
Aoyama, T. 1970 b: Tensioning of band saw blade by rolls. Part II (In Japanese) J. Japan Wood Res. Soc. 16:376–381
Aoyama, T. 1971 a: Tensioning of band saw blade by rolls. Part III. (In Japanese) J. Japan Wood Res. Soc. 17:188–195
Aoyama, T. 1971 b: Tensioning of band saw blade by rolls. Part IV. (In Japanese) J. Japan Wood Res. Soc. 17:196–202
Aoyama, T. 1974: Tensioning of band saw blade by rolls. Part V (In Japanese) J. Japan Wood Res. Soc. 20:523–527
Aoyama, T.; Ohmori, Y. 1977 a: tensioning of circular saw blade by stretcher, Part I (In Japanese) J. Japan Wood Res. Soc. 23:280–285
Aoyama, T.; Ohmori, Y. 1977 b: Tensioning of circular saw blade by stretcher, Part II. (In Japanese). J. Japan Wood Res. Soc. 23:286–289
Bajkowski, J. 1967 a: Spannungsverteilung in durch Walzen vorgespannten Gattersägeblättern (Distribution of stresses in framesaw blades prestressed by rolling) Holztechnologie 8:258–262. Environment Canada Translation No. 868
Bajkowski, J. 1967 b: Einfluß des Vorspannens durch Walzen der Gattersägeblätter auf ihre Starrheit. (Influence of roller induced stresses on the stiffness of frame-saw blades). Holztechnologie 8:194–199
Barz, E. 1960: Prüfgeräte für den Richt- und Spannungszustand von Kreissägeblättern. (Testing devices to determine straightening and tension condition of circular saws). Holz Roh- Werkstoff 18:19–25 CSIRO Australia Translation No. 5175
Barz, E. 1962: Der Spannungszustand von Kreissägeblättern und seine Auswirkung auf das Arbeitsverhalten. (The stress state of circular saws and its effect on the working behavior). Holz Roh-Werkstoff 20:393–397CrossRef
Barz, E. 1963: Vergleichende Untersuchungen über das Spannen von Kreissägeblättern mit maschinen und mit Richthämmern (Comparative studies of tensioning of circular sawblades with machines and by hammering) Holz Roh- Werkstoff 21:135–144. CSIRO Australia Translation No. 6583
Beer, R.; Peterschinegg, H. 1977: Reckvorspannung in Kreissägeblättern. (Stresses in circular sawblades). Öster. Ing.-Z. 20:155–162
Dugdale, D. S. 1963: Effect of internal stress on the flexural stiffness of discs. Int. J. Engin. Sci. 1:89–100CrossRef
Dugdale, D. S. 1965: Flexure tests for revealing internal stress in disks. Int. J. Engin. Sci. 3:1–8CrossRef
Dugdale, D. S. 1966 a: Stiffness of a spinning disc clamped at its centre. J. Mech. Phys. Solids. 14:349–356CrossRef
Dugdale, D. S. 1966 b: Theory of circular saw tensioning. Int. J. Prod. Res. 4:237–248
Dugdale, D. S. 1967: Internal stress in tools. Strain 3:13–15CrossRef
Foschi, R. O. 1975: The light gap technique as a tool for measuring residual stresses in bandsaw blades. Wood Sci. Technol. 9:243–255CrossRef
Grube, A. E.; Sanev, V. N., Pashov, V. K. 1967: Automatic control of the thermal stresses in disk saws. Derevoobrabatyvayushchaya Premyshlennost. 16:4–6. Kresge Hooker Science Library Translation 18508c
Hackenberg, P. 1975: Thermisches Vorspannen von Kreissägeblättern. (Heat tensioning of circular saws). Werkstattstechnik 65:81–86
Huber, H. 1977: Residual stresses in circular saws introduced by mechanical and thermal means. Proc. Fifth Wood Machining Seminar: 44–58. University of California Forest Products Laboratory, Richmond, CA.
Kimura, S. 1976: Studies on tensioning of circular saw by rolling pressure, Part III. (In Japanese). J. Japan Wood Res. Soc. 22:343–348
Kimura, S.; Ando, M. 1974: Studies on tensioning of circular saw by rolling pressure, Part I. (In Japanese). J. Japan Wood Res. Soc. 20:196–204
Kimura, S.; Asano, I. 1976: Studies on tensioning of circular saw by rolling pressure, Part IV (In Japanese). J. Japan Wood Res. Soc. 22:387–392
Kimura, S.; Asano, I. 1980: Studies on tensioning of circular saw by rolling pressure, Part V. (In Japanese). J. Japan Wood Res. Soc. 26:790–795
Kimura, S.; Ito, M. 1976: Studies on tensioning of circular saw by rolling pressure, Part II. (In Japanese). J. Japan Wood Res. Soc. 22:139–145
Kirbach, E.; Bonac, T. 1978: The effect of tensioning and wheel tilting on the torsional and lateral fundamental frequencies of bandsaw blades. Wood and Fiber 9:245–251
MacBain, J. C.; Horner, J. E.; Stange, W. A.; Ogg, J. S. 1979: Vibration analysis of a spinning disk using image-derotated holographic interferometry. Exper. Mechs. 19:17–22CrossRef
McKenzie, W. M. 1969: How does heat tensioning of saw blades work? CSIRO Forest Prod. Newsletter 363:2–3
McKenzie, W. M. 1971: Sawblade tensioning—what is it all about? CSIRO Forest Prod. Newsletter 383:2–4
Möller, E.; Ringh, U. 1982: A method to observe and record vibration modes of rotating circular objects. Exper. Mechs. 22:226–230CrossRef
Mote, C. D., Jr. 1965 a: Free vibration of initially stressed circular disks. J. Engin. Ind. 87:258–264
Mote, C. D., Jr. 1965 b: Some dynamic characteristics of band saws. Forest Prod. J. 15:37–41
Mote, C. D., Jr.; Nieh, L. T. 1973: On the foundation of circular-saw stability theory. Wood and Fiber 5:160–169
Mote, C. D., Jr.; Schajer, G. S.; Holøyen, S. 1981: Circular, saw vibration control by induction of thermal membrane stresses. J. Engin Ind. 103:81–89
Mote, C. D., Jr.; Schajer, G. S.; Wu, W. Z. 1982: Band saw and circular saw vibration and stability. Shock and Vibr. Dig. 14:19–25CrossRef
Mote, C. D., Jr.; Szymani, R. 1977: Principal developments in thin circular saw vibration and control research, Part I. Holz Roh-Werkstoff 35:189–196CrossRef
Münz, U. V. 1979: Vorspannungszustand und Arbeitsverhalten von Kreissägeblättern. (Pretensioning and work behavior of circular saw blades) Holz Roh- Werkstoff 36:345–352CrossRef
Münz, U. V. 1980: Mechanisch und thermisch erzeugte Spannungen in Kreissägeblättern. (Mechanically and thermally induced tensions in circular saw blades). Holz Roh- Werkstoff 38:201–208CrossRef
Pahlitzsch, G.; Friebe, E. 1973 a: Über das Vorspannen von Kreissägeblättern, Part I. (On tensioning of circular sawblades). Holz Roh- Werkstoff 31:429–436
Pahlitzsch, G.; Friebe, E. 1973 b: Über das Vorspannen von Kreissägeblättern, Part II. (On tensioning of circular sawblades). Holz Roh- Werkstoff 31:457–463
Pahlitzsch, G.; Friebe, E. 1974: Über das Vorspannen von Kreissägeblättern, Part III. (On tensioning of circular sawblades). Holz Roh- Werkstoff 32:5–12. Environment Canada Translation No. 844CrossRef
Quinn, R. S. 1967: A report on heat tensioning. Forest Ind. 94:99
Rhemrev, J.; Trinchera, L. 1978: Improving the stability of thin circular saws through applied research. Paper presented at the 32nd annual meeting of the Forest Prod. Res. Soc., Atlanta, GA
Sack, R. A. 1954. Transverse oscillations in travelling strings. Brit. J. Appl. Phys. 5:224–226CrossRef
Schajer, G. S. 1979: Circular saw natural frequency program SAWFQ2. Technical Report No. 35.01.130. Progress Rep. No. 13. University of California Forest Prod. Lab., Richmond, CA
Schajer, G. S. 1981: Analysis of roller-induced residual stresses in circular discs and their effect on disc vibration. PhD dissertation, University of California, Berkeley
Schajer, G. S.; Mote, C. D., Jr. 1983: Analysis of roll tensioning and its influence on circular saw stability. Wood Sci. Technol. 17:287–302CrossRef
Schajer, G.S.; Mote, C.D., Jr. 1984: Analysis of optimal roll tensioning for circular saw stability. Wood and Fiber Sci. 16: in print
Strzelecki, A. 1977: Vibrations of the circular saw. Proceedings of the Fifth Wood Machining Seminar. 33–43. University of California Forest Prod. Lab., Richmond, CA
Szymani, R.; Mote, C. D., Jr. 1974: A review of residual stresses and tensioning in circular saws. Wood. Sci. Technol. 8:148–161CrossRef
Szymani, R.; Mote, C. D., Jr. 1977 a: Principal developments in thin circular saw vibration and control research, Part 2. Holz Roh-Werkstoff 35:219–225CrossRef
Szymani, R.; Mote, C. D., Jr. 1977 b: Circular saw stiffness as a measure of tension. Forest Prod. J. 27:28–32
Szymani, R.; Mote, C. D., Jr. 1979: Theoretical and experimental analysis of circular saw tensioning. Wood Sci. Technol. 13:211–237CrossRef
Ulsoy, A. G.; Mote, C. D., Jr. 1980: Analysis of bandsaw vibration. Wood Sci. 13:1–10
Ulsoy, A. G.; Mote, C. D., Jr. 1982: Vibration of wide band saw blades. J. Engin. Ind. 104:71–78CrossRef
Ulsoy, A. G.; Mote, C. D., Jr.; Szymani, R. 1978: Principal developments in band saw vibration and stability research. Holz Roh-Werkstoff 36:273–280CrossRef
Wu, W. Z. 1982: The vibration and stability analysis of axially moving materials: a special study on band saw systems PhD dissertation, University of California, Berkeley.
Wüster, E. Die Berechnung der Reckvorspannungen in Gatter- und Bandsägeblättern. (Calculation of the stresses in gangsaw and bandsaw blades caused by tensioning). Holz Roh- Werkstoff 24:134–144
Yakunin, N. K. 1980: Rolling of saws. Derevoobrabatyvayushchaya Promyshlennost. 11:9–13.


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## woodbrains (10 Apr 2016)

Hello,

Wow, thanks Corneel, I'll give it some time to read tomorrow. 

I do think that I have stumbled on a good theory, though. If the grain structure in stress hardened steel is different ( it is) than the unhardened steel, then it is, in fact a different material, albeit slightly, which will have different properties of stiffness, elasticity, brittleness, etc. etc. albeit slightly, it must still be different. So should be assumed that it can no longer be directly comparable, any more than a piece of plastic or brass or whatever, of the same dimensions, can be compared to the steel in its unhardened state. How could it, really?

Mike.


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## Cheshirechappie (11 Apr 2016)

Mike, you're right that the grain structure of steels is different depending on their heat-treatment condition (annealed, hardened right out, hardened and tempered back), but that won't affect their stiffness (or more technically, their elasticity below yield point). It will drastically affect their yield point and ultimate tensile strength, though.

Earlier in the thread, AndyT mentioned the book, "The New Science of Strong Materials" by J E Gordon. I'd heartily endorse his recommendation. For anybody wanting a deeper understanding of the metallurgy of steels (and other metals), a copy of "Engineering Metallurgy" volume I by R A Higgins should cure any insomnia, but also explain what's going on with grain structure when metals are worked or heat treated.

However, most saw doctoring is about the manipulation of internal stresses, not about grain size modification. Saw blades start out hardened and tempered, so the grain structure is pretty well set by that condition.

I'm a little bit wary of drawing comparisons between circular saws, band saws and hand saws. The reason is that both circular and band saws see stresses in service that handsaws don't. 

A circular saw develops stresses in the plate as it spins, and the heat generated in cutting cause thermal expansion of the rim. It was found during the development of such saws during the early to mid 19th century that the detrimental effects those stresses could be alleviated by doctoring the saw before service - basically making it a flat cone or flat saucer shape instead of dead flat. The larger the saw, the more important the pre-service doctoring. The early texts such as 'Grimshaw on Saws' deal with this in some depth - many pages on circular saw doctoring, against a bare couple of pages on handsaws. It's interesting that vibration becomes a factor as rotational speeds increase, and that it's deleterious effects can be reduced by saw doctoring.

A band saw, when in service, IS under tension - that imparted by the top wheel adjustment mechanism. It will also see the load applied by the material being fed to it, and the balancing loads applied by the guide wheels to the back of the blade.

Handsaws see none of these loads - indeed, the stresses on a decently sharp hand, panel or backsaw are very low (you don't need to apply much force to get it to cut, just move it backwards and forwards). What stresses there are will be at the tooth-work interface, and mostly near the working bit of the tooth, the tip. The main body of the saw blade will see pretty well the same stresses it sees when lying on the bench. Thus, circular saw and bandsaw type 'tensioning' are not needed.

Maybe as the saw makers were wrestling with the problems of making reliable circular saws, they thought that the lessons they were learning could be applied to hand saws. I'm not at all sure that it actually does anything worthwhile to the hand saw blade, but it doesn't half sound good in the marketing blurb!


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## Corneel (11 Apr 2016)

First you tried to tell us that tensioning of sawblades is not possible. That hammering on sawblades didn't do anything for the tension in the blades. Now I gave you a few references where tensioning of sawplates is described, calculated and the effect meassured. And now this all suddenly doesn't apply to handsaws?

As far as I know, hammer tensioning came first on handsaws, and was later applied to circular and bandsaws to cure problems with these. And bandsaws might be under tension, but they have the problem that they find a block of wood in their path. This block of wood slows down the blade, while the motor tries to pull it through. The result is vibrations, and the cure for these vibrations is hammer or roller tensioning.

The effect of hammer tensioning is real. You could at least admit that. Then we could see if it actually does any good to a handsaw.


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## Cheshirechappie (11 Apr 2016)

Corneel - I've stated that you can't STIFFEN a hand saw blade by hammering it (or rolling it, or whatever). I've put forward a hypothesis about what 'tensioning' might do to a hand saw blade, by the effects of manipulating internal stresses. I haven't said that 'tensioning' doesn't exist - it's just that nobody has yet explained what it is (I don't know either), though one or two have jumped to unsubstantiated conclusions. 

The things done to circular and band saw blades are different because they operate under different conditions, and see radically different stresses to handsaws.


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## D_W (11 Apr 2016)

Two things are mentioned for tensioning:
* stiffening the saw
* increasing the likelihood that the saw returns to straight.

If the tensioning isn't why two of my saws with similar cross section are different in stiffness, I'll gladly take the benefit of the latter.

I doubt there's going to be much literature on tensioning anything other than bandsaws and circular saws for the simple reason that research and documentation would've been met with economic reward with those two. Not since the early 1900s for hand saws, and in that case, in an ultra competitive business where makers did most of the research, I can't see why we'd expect they'd have offered anything other than ad copy publicly.


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## Cheshirechappie (11 Apr 2016)

D_W":1g5yhsyl said:


> Two things are mentioned for tensioning:
> * stiffening the saw
> * increasing the likelihood that the saw returns to straight.



Can anybody post a reference that states that 'tensioning' stiffens a hand saw blade? I've read a fair bit about saws, though I very much doubt I've read everything, but I can't recall ever having seen any statement to that effect. Most of the references, when they mention 'tensioning' at all, are pretty vague about what it is or what it does.


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## D_W (11 Apr 2016)

Cheshirechappie":3p7nmkvp said:


> D_W":3p7nmkvp said:
> 
> 
> > Two things are mentioned for tensioning:
> ...



There is an article by Bob Smalser where he states both of the above. If we're looking for something in an engineering journal, I think we might as well just hit repeat on the thread as we've gone through that. Thus my comment from above - I don't think it was something that would've been studied at a university level (especially not in the interest of making information public). 

The later study material is for things that are commercially viable. 

Sort of like the cap iron study - it was not done for planes. It was done for the marunaka super surfacer (which you can look up, you'll know you've seen it if you can't visualize what it is). There was, however, an ancillary paper written for planes, but i think that was out of good intention by the university, and they weren't very precise about that part itself. People are running around quoting distances for cap irons that are in regard to machine testing, but the paper the same university released on the hand plane was much less committal about specifics and instead said that it's a matter of experimentation to get the cap iron in a plane set properly.


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## Cheshirechappie (11 Apr 2016)

If the Bob Smalser article you refer to is the one about saw straightening, I know the one you mean. He makes a number of statements in that article that he doesn't provide any references for. Have you any idea where his statements came from?

In the 19th and early 20th century literature, I can't recall seeing any statement to the effect that 'tensioning' makes a hand saw blade stiffer. 'Tensioning' is mentioned a several references, but as I said earlier, always in rather vague terms.


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## Corneel (11 Apr 2016)

I just gave about 60 references about tensioning or pre-stressing of saw blade material. They compress the blade material in a lot of small spots which puts tension in the plate. There is no reason why that wouldn't work on handsaw blade material too. This has already been worked out, calculated and tested back in the 60's- 80's.

It helps to reduce low frequency vibrations. And that is something very usefull for a handsaw too. When you trust the sawplate down into the wood, the forward trust is resisted by the wood cutting action. This would buckle the plate if it is too thin and thus create low frequency vibration. On the back stroke it is also very easy to excite a low frequency vibration, you probably know the annoying flapping of a floppy blade when you don't pull it back exactly straight through the cut.

Hammer tensioning helps to make a blade resist those vibrations so you can use a thinner blade. There is no market for high quality handsaws anymore, so there is no money for research. But there are strong analogies with the powertool blades. How it is done is explained, calculated and tested in those papers I mentioned above. Before this scientific research it was more like a craft, well known among seasoned sawmakers, but not described in detail anywhere.


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## Cheshirechappie (11 Apr 2016)

Corneel":pz2rhpj0 said:


> I just gave about 60 references about tensioning or pre-stressing of saw blade material. They compress the blade material in a lot of small spots which puts tension in the plate. There is no reason why that wouldn't work on handsaw blade material too. This has already been worked out, calculated and tested back in the 60's- 80's.
> 
> It helps to reduce low frequency vibrations. And that is something very usefull for a handsaw too. When you trust the sawplate down into the wood, the forward trust is resisted by the wood cutting action. This would buckle the plate if it is too thin and thus create low frequency vibration. On the back stroke it is also very easy to excite a low frequency vibration, you probably know the annoying flapping of a floppy blade when you don't pull it back exactly straight through the cut.
> 
> Hammer tensioning helps to make a blade resist those vibrations so you can use a thinner blade. There is no market for high quality handsaws anymore, so there is no money for research. But there are strong analogies with the powertool blades. How it is done is explained, calculated and tested in those papers I mentioned above. Before this scientific research it was more like a craft, well known among seasoned sawmakers, but not described in detail anywhere.



OK. So all we need now is a demonstration of that working on a hand saw blade. Somebody taking a cheap, floppy, unhammered saw, giving it the hammer treatment, and demonstrating that it's then stiffer. Or taking two pieces of identical spring steel, hammer treating one, and demonstrating a significant difference in stiffness between the 'tensioned' and the 'untensioned'.

I don't think anybody will be able to demonstrate it, for all the reasons set out in this thread. However, there are those who say that a hand saw blade can be stiffened by hammering (or rolling, or whatever). OK - prove it.


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## D_W (11 Apr 2016)

Cheshirechappie":151c8n4z said:


> Corneel":151c8n4z said:
> 
> 
> > I just gave about 60 references about tensioning or pre-stressing of saw blade material. They compress the blade material in a lot of small spots which puts tension in the plate. There is no reason why that wouldn't work on handsaw blade material too. This has already been worked out, calculated and tested back in the 60's- 80's.
> ...



Here's the difference between real life and the engineering answer. Engineers assume that the knowledge is difficult but the proving is easy ("the whole world is built by engineers" who couldn't butter a brick if you gave them two hours). What you're not grasping is there's no documentation on the rolling or hammering, so what you'd like to prove and what you asserted at the beginning (that tensioning doesn't do anything), you can't prove. You can't prove anything about it because you have no clue whether or not it's done correctly.


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## Cheshirechappie (11 Apr 2016)

D_W":2b6dmse9 said:


> Cheshirechappie":2b6dmse9 said:
> 
> 
> > Corneel":2b6dmse9 said:
> ...



Should be easy enough to demonstrate. Take one floppy saw, hammer it, demonstrate that it's now stiffer. You've been telling us all thread that that is what happens - 'tensioning' makes a hand saw blade stiffer.

To be frank, I'm getting bored with this thread, and people making assertions they can't prove - namely, that 'tensioning' a hand saw blade by hammering it makes it stiffer. I say it doesn't.

Well, now's your chance to prove that it does.


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## D_W (12 Apr 2016)

Cheshirechappie":11pilu0w said:


> Should be easy enough to demonstrate. Take one floppy saw, hammer it, demonstrate that it's now stiffer. You've been telling us all thread that that is what happens - 'tensioning' makes a hand saw blade stiffer.
> 
> To be frank, I'm getting bored with this thread, and people making assertions they can't prove - namely, that 'tensioning' a hand saw blade by hammering it makes it stiffer. I say it doesn't.
> 
> Well, now's your chance to prove that it does.



Ahh, the engineer's take again. The solution is in our heads, but once we know it, then it's very easy and trivial to carry out. Of course, you are still ignoring the fact that you have no clue how you would hammer a saw to tension it, and in tensioned saws (circular), where the properties are not at all in dispute, you wouldn't be able to hammer that or tell someone where or how to hammer, either. It would take a skilled sawsmith to do that. Just as it would take a skilled smith to prove something on a handsaw. 

If you think you're getting tired of it, imagine how tired everyone else is getting with attempts at theoretical talk when you don't even know what you're arguing against. How could you know what you're arguing against when you don't even know what a sawsmith would do to tension a saw?

Really, I'm tired of it, too. I have top line saws that are stiffer than third line saws I've had of the same cross section, and no amount of supposition on your part will change that. 

(I recognize not every engineer is similarly afflicted with this disease where all things are better solved in discussion rather than carried out in practice).


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## Corneel (12 Apr 2016)

I was called early this morning for an emergency, but everything is quiet again. I'm sitting behind my desktop at work, so I can access the Springer articles again. I scanned the article I posted a link, and this page explains exactly what we have been talking about all the time. It is about bandsaws. Those blades are under tension when the bandsaw is not running, but as soon as it starts running the tensions around the piece of wood being cut is compromised and waves in the blade are possible, hey, just like a handsaw!

Speeds in a bandsaw are higher, but the exact same thing happens in framed gangcutting blades at a sawmill. Pretensioning the blade with one of the methods like hammer tensioning is being done here too, and speeds in those mills are more alike a handsaw used in anger.

I am not going to run experiments with bits of sawplate. I don't have the time and like David wrote, hammer tensioning is an art. Learning to tension and flatten a sawblade usually took up to 6 months of learning on the job. And I also don't need to do the experiment, it has allready been done. It was also done on millions of handsaws at the Disston, Spear and Jackson, Kenyon, Greeves etc saw factories.


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## Cheshirechappie (12 Apr 2016)

D-W - On page 1 of this thread, you told us all how to 'tension' a saw.



D_W":1kcn6lsz said:


> Rhyolith":1kcn6lsz said:
> 
> 
> > I friend wants to know how to re-tesion panel saws (if they get bent or other wise damaged).
> ...



The 'Engineer's Approach' you take such delight in looking down on is often quite simple - just do it, and prove it works. If the likes of Spear and Jackson, Kenyon etc etc were doing it a hundred years ago, it can be done again. Take a piece of spring-steel, or a cheap, floppy, untensioned saw, hammer it as you described, and demonstrate that it can make the saw stiffer.

I say it won't work on a hand saw, and have tried to explain why it won't work. (I've tried to explain why circular and band saw blades are different, too, and why manipulating shape and residual stresses can be beneficial to them.) You say it does work on hand saws. OK - prove it.


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## Corneel (12 Apr 2016)

You haven't quite explained why and how bandsaw blades are different.


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## Cheshirechappie (12 Apr 2016)

1) They are under a uniform, externally-applied tension (from the adjuster on the bandsaw top wheel) - not applicable to hand saws.

2) They have two guide rollers at the back of the blade opposing the feed load - not applicable to hand saws.

3) The feed load is significant, and causes the band to be effectively a simply-supported beam with a more-or-less uniformly distributed load. That causes the loaded band to be in additional tension at the back, and adds compression at the toothed front. When the band is off the saw, adding some residual tension to the front adds to the band-stretch tension, and offsets some of the feed compression, thus allowing higher loading (faster feed rate). Again, not applicable to hand saws, on which the feed loads are very small.

4) It seems that at increased band speeds and feed loads, vibration can become a problem. Again - not applicable to hand saws - nobody is going to get them up to those speeds or feedrates.


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## Corneel (12 Apr 2016)

You can also look at it differently. A bandsaw is under tension, the blade is fully supported at the cutting end with the guide rollers. And still it is capable of low frequency vibrations. They solve this problem (up to a point) with hammer tensioning the tooth line.

A handsaw isn't supported in any kind like a bandsaw blade is, so it is in a worse situation. It is also quite possible to get undesirable low frequency vibrations. So the characteristics of the cutting action can be improved with hammer tensioning the blade, especially the tooth line. This allows to use a thinner blade then would otherwise be possible.

Modern manufacturers of disposible handsaws simply increase the plate thickness. Disston et. al. used hammer tensioning and roller tensioning to be able to use thinner blades, even grinded thinner towards the back (taper grinding). Those saws work very nicely despite those thinner blades.


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## CStanford (12 Apr 2016)

CC you said:

The 'Engineer's Approach' you take such delight in looking down on is often quite simple - just do it, and prove it works. If the likes of Spear and Jackson, Kenyon etc etc were doing it a hundred years ago, it can be done again. Take a piece of spring-steel, or a cheap, floppy, untensioned saw, hammer it as you described, and demonstrate that it can make the saw stiffer.

I say it won't work on a hand saw, and have tried to explain why it won't work. (I've tried to explain why circular and band saw blades are different, too, and why manipulating shape and residual stresses can be beneficial to them.) You say it does work on hand saws. OK - prove it.

I suppose a theory about why these firms "were doing it" would be more into the realm of psychology (some sort of mass delusion?) but still I'd be interested in your personal theory about why these firms bothered hammering their top of line saws, and paid what has been described as 'highly skilled' smiths to do it, presumably at a higher wage to account for their special skill. The process has been described in links already provided as something quite distinct from straightening, etc. so that's not it. Was it all just a marketing farce common amongst all firms?

Otherwise, the bulk of your argument seems to be a challenge to reproduce a skill that is widely acknowledged to be one in danger of being lost. In other words, if an 'every man' can't do it this somehow stands as proof.


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## Cheshirechappie (12 Apr 2016)

Corneel":13brm47y said:


> You can also look at it differently. A bandsaw is under tension, the blade is fully supported at the cutting end with the guide rollers. And still it is capable of low frequency vibrations. They solve this problem (up to a point) with hammer tensioning the tooth line.
> 
> A handsaw isn't supported in any kind like a bandsaw blade is, so it is in a worse situation. It is also quite possible to get undesirable low frequency vibrations. So the characteristics of the cutting action can be improved with hammer tensioning the blade, especially the tooth line. This allows to use a thinner blade then would otherwise be possible.
> 
> Modern manufacturers of disposible handsaws simply increase the plate thickness. Disston et. al. used hammer tensioning and roller tensioning to be able to use thinner blades, even grinded thinner towards the back (taper grinding). Those saws work very nicely despite those thinner blades.



OK - if, as you suggest, hammering a hand saw blade does something beneficial to it (makes it stiffer, makes it less liable to vibrate, whatever), then demonstrate the fact. At the moment, it's all just assertion and speculation, no clear, unambiguous demonstration.

Earlier in the thread, I posited a hypothesis about what hammering (rolling, whatever) might do to a hand saw blade that would be beneficial to it, other than straightening it after heat treatment. I've no idea whether the hypothesis is right or wrong, it's just a hypothesis, that's all.

Why did Spear and Jackson, Disston et al hammer their hand saw blades? Mainly to get them flat. Any other effect is unproven and undemonstrated - so far. And Charles - maybe, just maybe, the fact that nobody can manage to stiffen a hand saw blade by hammering it is an indication that it doesn't work. I don't accept the idea that if people did it in the late 19th century, it can't be done today. They hammered hand saws in the late 19th century - to get them flat, not to make them stiffer.


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## CStanford (12 Apr 2016)

CC, they did not hammer the saws exclusively for the purpose of making them straight. 

"Tensioning" was reserved for higher end saws, at least in Spear and Jackson's case. Unless they sold all their lower-end saws with a slow bend in them, you are completely wrong or would need to explain why they would make their lower end saws straight by some other method and reserve the expensive, laborious method for their best-quality saws.

I'm reasonably sure there are still people out there tensioning saws, Bob Smalser appears to be one, your insistence on finding one on this particular forum (a not particularly heavily traveled one at that) leaves one baffled by your contorted logic and what this means in the real world.

Perhaps all that is needed is a broadening of your horizons?


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## Corneel (12 Apr 2016)

If the behaviour of a saw blade in regards to vibration control can be changed by hammering a bandsaw blade (that one is proven beyond doubt), then I don't see a reason why you can't change the behaviour in a handsaw. How benificial it really is in a handsaw is not proven in a scientific way. Probably never will.


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## Cheshirechappie (12 Apr 2016)

CStanford":26o8rvlq said:


> CC, they did not hammer the saws exclusively for the purpose of making them straight.
> 
> "Tensioning" was reserved for higher end saws, at least in Spear and Jackson's case. Unless they sold all their lower-end saws with a slow bend in them, you are completely wrong or would need to explain why they would make their lower end saws straight by some other method and reserve the expensive, laborious method for their best-quality saws.
> 
> ...



Perhaps all that is needed is for those claiming that 'tensioning' does something noticeable (such as stiffening it) to a hand saw blade to demonstrate the fact. If there are people out there tensioning saws, that shouldn't be too difficult to do.


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## CStanford (12 Apr 2016)

There was/is a demonstrable difference or sane, honest firms like Spear & Jackson would not have engaged in the practice. They were doing it as late as the mid-1960s and perhaps later. I would think the most likely reservoir of old craftsmen is in England, though my guess is that the ones still living are not internet savvy.

I'm not sure how one would demonstrate 'stiffness' via the internet without some elaborate laboratory procedure. So, you see, you've set yourself up to have 'won' the argument more or less by default. Your only problem is that the history of the practice speaks to its legitimacy more than your strident arguments otherwise. It's easy to walk into a room and make the announcement that you'll only believe in black holes when somebody can provide, and explain, a mathematical model for their existence. And you proceed to do this in a room full of people who never took a math course after Algebra II. Therefore, black holes do not exist. Your limited audience could not provide you with the necessary rigorous proof.

I do not currently own any top-of-the line antique saws. I have in the past. They did seem stiffer than a cheaper 'warranted superior' saw but they were not alike enough in other ways to draw a conclusion from my obviously limited experience.

Again, they had other means of straightening the saws. They were straight by the time they arrived at the bench of the craftsman who would tension the, again, top of the line saw. Something was occurring. It beggars belief that it was all a ruse or silly superstition. They paid people to do this work.


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## Cheshirechappie (12 Apr 2016)

Charles - all sorts of people SAY all sorts of things about 'tension' in hand saw blades. All I'm suggesting is that the questions and doubts could be laid to rest if someone, somewhere, demonstrates beyond doubt that there's a way to make hand saw blades stiffer (or whatever) by hammering them (or whatever), and demonstrates it by doing it.

So far, lots of words, lots of ideas, lots of assertions. But no proof or demonstration (that I know of) that 'tensioning' a hand saw blade does anything noticeable to it.


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## CStanford (12 Apr 2016)

It might be helpful if you would describe exactly what proof or a demonstration would need to look like to satisfy you.


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## MIGNAL (12 Apr 2016)

Not difficult to prove. Difficult to organise and you would need people sufficiently interested in taking part. You just need someone who can tension a saw and a handful or two of experienced woodworkers. Same saw type of course, one 'tensioned' the other not. The woodworkers aren't told which is which but they have to pick out the 'better' saw.


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## CStanford (12 Apr 2016)

That's pretty much how I'd do it but I sense that CC would not be satisfied with the methodology.

I'd love to hear anybody's theory about why any of the major manufacturers would pay guys to beat on already straight and otherwise presumably salable saws if there were no effect from the exercise. I admit to be a bit stuck on this point.


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## Cheshirechappie (12 Apr 2016)

Oh I dunno, sounds as good as way as any. Two identical saws, one tensioned and one not. Blind testing by independent woodworkers.

Another way might be to obtain a fresh saw blade, measure its stiffness, tension it, and then measure its stiffness again by the same method. See if there's a difference. I'm sure other people could come up with other methods, too.

As to why major manufacturers etc etc. Erm, did they? We know they had to smith saws straight as many as three times - once after heat treatment, once after grinding and once after polishing (or 'rubbing'). So if they did hammer-tension, they had three opportunities to do it. Simon Barley's account of saw making suggests that it came under 'smithing', the first of three hammering stages. The 1844 list of prices he shows on page 6 of 'British Saws and Saw Makers' gives prices for 'smithing', 'hammering' and 'blocking', but does not mention 'tensioning'.


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## Carl P (12 Apr 2016)

I suggest we find someone who can do this, if we can, we use some form of crowdsourcing to fund the commissioning of two saws, possibly with video/text explanation, the saws open to be tested by whoever, and would end up as the property of an appropriate museum, as would rights to any video/text, I've sent a message to the Ken Hawley trust, perhaps a member of TATHS could contact them, and anywhere else people can think of,

Cheerio,

Carl


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## CStanford (12 Apr 2016)

As mentioned in Spear and Jackson's Story of the Saw, tensioning by hammering was reserved for only top shelf models. The others had to have been made straight by another method (why hammer to make straight and not 'tension' the saw too?) which logically implies that they arrived at the bench to be tensioned already straight and in essentially salable condition except for the application of a little whipped cream on top (tensioning).

Phew, long sentence. Sorry.


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## Corneel (13 Apr 2016)

Two links to other forums.

Rob Steeper has done a lot of research into old Disston plates, how they were hammered and trying to replicate it. You should read this thread on woodworkforums to see some of his results. After hammering two lines, one along the back, one through the middle of the saw plate, the plate still has the same eleasticity, but now more even from one side compatred to the other. But the plate feels "snappier" and oscillates less. 

http://www.woodworkforums.com/f278/hammering-hand-blades-196658

Another forum, where a guy named Diabolo explains the tensioning process and the why of it all in regards to large crosscut saws.

http://www.crosscutsawyer.com/viewtopic.php?f=4&t=750

I read a German article about pretensioning on large frame saws like they use in a mill. They run three lines along the length of the sawblade, one in the middle and two on each side of this, with a narrow roller. This tries to expand the steel in the length. And this causes the toothline and the back to be in tension. In this diagram you see various tensions in the blade. In the top you see the tensions seperately, at the bottom you see the resultant of all of them combined. As you can see the tension from the rolling process exceeds the tension from the frame. This to give you an idea of the forces involved and what actually happens. The steel itself isn't changed, it's stiffness remains the same, but the tension of the steel changes. Next thing I am trying to grasp is what that actually means.


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## Cheshirechappie (13 Apr 2016)

That's a bit more like it - reference to somebody actually trying instead of just making unsupported assertions. As far as we can tell so far, Rob's experiments are in an early stage, but whilst most of the hammer work to his saw blades is about getting them flat and straight - getting the sheetstock coil curve out of them - there does seem to be a hint of something going on amongst it all. Only a hint, though. Interesting - one to watch. It's also interesting that others have gone through the same sort of discussion that we've had on this thread (albeit rather more concisely) with about the same general results.

The Crosscutsawyer forum link is the same one that Mignal posted on page 5 of the thread.

I'm not sure about the frame saw reference yet. I've got places to go now, but I'll have a think about it. Would help if I could translate the German on the graph - a short session with Google Translate later, I think!


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## CStanford (13 Apr 2016)

Excerpt from post and links on page 10 of the thread:

"The UltraSTEELTM process, developed by Hadley Industries Plc (Hadleys), is a novel surface dimpling process used on steel strip prior to cold roll forming. This dimpling process increases the strength of the final rolled products and enhances other product properties such as fire test performance and screw retention."

C. J. Wang, D. J. Mynors, M. English, "Simulating the UltraSTEELTM Surface Dimpling Process", Key Engineering Materials, Vols. 410-411, pp. 449-456, 2009

This is a UK company and the professional journal being referenced a UK one as well if I'm not mistaken.

Something happens when you dimple the surface of sheet steel besides making a cute little mark.


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## Corneel (13 Apr 2016)

Link to the German article: http://link.springer.com/article/10.1007/BF02608078#page-1

It's a pitty you can only read it when you happen to be in an academic environment (like our hospital). I am still digesting this article.


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## Corneel (13 Apr 2016)

I think I have an explanation for the words fast and loose. Loose are the areas in the plate under compression, fast are the areas under tension. During the flattening and straightening procedure, the sawdoctor will use hammers on an anvil to create or remove fast and loose points, just as neccessary to create a flat plate. During the tensioning process this is done in a more structural way. A narrow path along the length of the plate, usually in the middle is hammered and thus made loose. The toothside and the back then become fast. 

Straightening, flattening and tensioning all use the same tools and work methods, so it is no wonder they get mingled. Especially when public relations write about it. It is very well possible that one man in one run flattens the plate and tensions it at the same time, without a layman seeing the difference. When they use a roller tension system, then it is a separate activity using a special machine. The effect of both procedures can be the same but the former asks for a lot more skill.


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## Corneel (13 Apr 2016)

In those German texts I found descriptions how the pretension in a sawplate is checked. They bend the saw and look for a lightgap between the plate and a straight edge. When the plate is properly tensioned it will be flat when you keep the saw straight like you would in normal use. It is flat lengthwise and crosswise. But when you set the plate in a slow bend along the length, the pre tensioned parts get the chance to release part of their tension by bending differently. The sawplate gets a curved cross section. The sawdoctors have measured this with the light gap, an old technique. One of those documents mentioned a lightgap of 0.4 mm for a properly tensioned framesaw blade as used in a sawmill. 

So I decided to have a look at the several old saws I have. I don't claim to be a sawdoctor, so take this with the usual grain of salt.

I have two Disston D8's from the 1930's. I have an older Spear and Jackson (no idea how old). And I have two Tyzacs, which also look rather old to me with the name punched into the plate, instead of etched.

First I looked at the straightness crosswise with the plate held straight. They were all flat or almost flat.

Then I bend the plate, pushing the toe against a stop on my bench and bending at the handle end. So I had a free hand to hold a straight edge against the plate, crosswise again, in the middle.

On both the D8's I couldn't detect much change, the plates still looked pretty flat crosswise.
The Tyzacs both showed a more convex surface on the outside of the bend in the plate. This corresponds with the information in the German texts for a tensioned blade. The convexity is not much, but I really have no idea how much it should be for a handsaw.
The Spear and Jackson has the most obvious convexity. I think I can even see how the plate is tensioned through the middle and along the back edge. I tried to shoot some pictures from the S&J. Hopefully you can see what I mean.

A picture with the sawplate straight, you can see that it is flat crosswise.




And a picture with the bend saw plate. Here you can see the effect of tensioning.




In use the two D8's both have the annoying flapping habbit on the return stroke. The S&J and one of the Tyzacs are nice saws. The last Tyzac isn't in working order at the moment.

So, overall, I would carefully conclude that this handsaw tensioning business is more then just a myth.


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## CStanford (14 Apr 2016)

Definitely something to it. Fascinating if the plate is convex on both sides, too. Is it?


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## Corneel (14 Apr 2016)

Not on both sides. When you bend the plate lengthwise it takes on an arched shape crosswise. So it is convex on the outside and concave on the inside of the bend. The pretension of the hammering process seeks to relieve itself a bit un this way.


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## Cheshirechappie (14 Apr 2016)

Corneel - I think you're on to something. What makes it interesting is that there is some accord with Rob Streeper's experiments. His hardness measurements of old saw blades suggested lines of (something) along the back and middle of the saw, and your bend-and-straightedge checks on your saws suggest something very similar. Also interesting that the saws that exhibit this tend to have less toe-end waggle in use.

It seems (from what we know so far) that the internal stresses of the blades are being manipulated. Earlier in the thread, we discussed this at some length, but always assumed that the whole blade was being treated. It seems that instead, internal stresses are modified only in bands along the saw.

All VERY interesting.


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## Corneel (14 Apr 2016)

Before we get too excited, I forgot to meassure the thickness of the blades. Behaviour of the saws depends a lot on the plate thickness too, and Disston did make them pretty thin. I'll check tonight, shouldn't take too much time.

Those bands of tensioning are similar to what I found for bandsaws and those saw mill frame saws, in the literature. You do need to make contrasting areas of compressed and tensioned steel, otherwise nothing happens.


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## CStanford (14 Apr 2016)

Bob Smalser:

http://www.wkfinetools.com/tRestore/saw ... Blade1.asp

"When a thin blade is struck on an anvil by a convex-faced round hammer, a dimple is created; often so small it can’t be seen by the eye. Steel from the area around the dimple is pulled inwards toward the point of impact, making the steel in the circular area radiating from the dimple stiffer, or “tensioned” on its surface. 

Hundreds of such hammer blows applied in certain patterns equally to both sides of a handsaw blade can make it stiffer, can true a warped circular sawblade, or can dish a large bandsaw blade to conform to its wheels while at the same time tensioning the cutting edge."

End quote.

"The UltraSTEELTM process, developed by Hadley Industries Plc (Hadleys), is a novel surface dimpling process  [well, perhaps not so novel] used on steel strip prior to cold roll forming. This dimpling process increases the strength of the final rolled products and enhances other product properties such as fire test performance and screw retention."


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## D_W (14 Apr 2016)

Corneel":2umo5lzp said:


> In use the two D8's both have the annoying flapping habbit on the return stroke. The S&J and one of the Tyzacs are nice saws. The last Tyzac isn't in working order at the moment.
> 
> So, overall, I would carefully conclude that this handsaw tensioning business is more then just a myth.



Not surprised to hear that late d8s are pretty floppy. I've had maybe half a dozen early d8s, and I had (until selling them last week) two later d8s. The early saws are stiff, but the later saws are not as stiff and the rest of the details don't look as good on them, either - the handles are blocky and the polish in the steel is more coarse.


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## Corneel (14 Apr 2016)

That would make them good candidates for some tensioning trials. Now I need two things: Time and Courage. I am a little afraid that I will turn them into pretzels.


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## CStanford (14 Apr 2016)

Why on earth would you risk it? You know it exists. If you have a well-tensioned saw be glad of it and let the naysayers be naysayers. Nothing to be gained. It's like looking yourself up in the phone book to make sure you've been spelling your name correctly.


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## pedder (15 Apr 2016)

Corneel":1ii4etqw said:


> And a picture with the bend saw plate. Here you can see the effect of tensioning.



Hi Kees,

I see two hollows. Not more not less. The rest is interpretation.

And I don't know how it got there. I can be an result of the grinding process. 
Bu I doubt it is the result of a hammering. It is too consistent for that.
Or do you say Disston rolled the tension in the blade?

Could you forward me the hole german text via email?

Cheers
Pedder


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## swagman (15 Apr 2016)

Kees. you may wish to make contact with Rob Streeper; Saw Maker from the USA.
Can be contacted via the Australian Woodwork Forum; Saws Handmade. 
Rob hammer tensions his saw plates, and has posted a number of threads on this subject.

http://www.woodworkforums.com/f278

Stewie;


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## Corneel (15 Apr 2016)

Yes I know about Rob Steepoer, I think I read all his threads overthere, but thanks for the tip anyway.

Pedder, I'll send you the texts I have found. 

I posted two pictures from my Spear and Jackson saw. The first is with the plate flat. You can see that the straight edge shows no hollows, it sits flat on the plate. The second picture is with the saw bowed in the length. Like a sector of a circle, radius probably 1 or 2 meter. Now I suddenly see those hollows appear. I tested on several places on the plate and found similar effect, but not all the way to the end. This behaviour shows that it is not from grinding.

This is exactly what you expect from a tensioned saw plate. The hammered or roled band along the length of the plate, through the middle, tries to elongate the sawplate. That is of course not possible, so it sets this centerline in compression, and the adjacent areas in tension. When you bow the plate, the compressed sector suddenly gets a chance to really extend the length, it simply bends a little further. That's what you see with the lightgap meassurement.

The Disston D8's didn't show this behaviour, and they behave more floppy in the cut. So that is why I carefully concluded that there might really be something in this tensioning theory.

The Disston D8's are 0.9 mm thick at the toothline, my English saws are 1 mm thick. This could also be a factor in the floppyness of the D8's, becasue a smaal decrease in thickness means a lot less stiffness.

So far it is all interpretation. It seems like a fun diversion though. I have some junker plates so maybe I'll try to find some time for experiments. Don't hold your breath though, this is going to take some effort.


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## Cheshirechappie (15 Apr 2016)

Corneel":1uyfk0fy said:


> Yes I know about Rob Steepoer, I think I read all his threads overthere, but thanks for the tip anyway.
> 
> Pedder, I'll send you the texts I have found.
> 
> ...



I agree that sorting it out won't be quick or easy. 

It seems that there has been some manipulation of internal stresses. Whatever was done stopped short of pushing the steel to yield point through it's full thickness because the blade's shape has not changed, which points to a modification of surface (or residual) stresses. Unfortunately, those are hard to measure, and outside the scope of 'home workshop' methods. Thus, we're left with observing the effects, which seem to be subtle rather than dramatic.

One of the difficulties in trying to draw too many conclusions from vintage saws is that we have no idea how much abuse they may have suffered during their life, or what effect that might have had.

Perhaps the best way to eliminate uncertainties - as said before - is to make two new saws, tension one, and compare. The obvious problem is in working out the details how the tensioning should be done. There may be some trial and error, here.

By the way, I tried the bend-and-straightedge test on a couple of my saws. The 1980s Robert Sorby (that states 'Tensioned Taper Ground Blade' on the blade) showed the bulges Corneel illustrated, but only to a very small, almost imperceptible, degree. The Groves, which is a much thinner blade and much older (stamp on middle of blade instead of etch, split sawnuts) did display the bulges to a more noticeable extent. It's a subtle thing to detect, though. A couple of 1930s or 1950s panel saws didn't show the phenomenon. I haven't checked all my saws yet, though.


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## Cheshirechappie (18 Apr 2016)

I refurbished the two panel saws mentioned in the last post over the weekend. Both were acquired a while ago via Ebay. The first is 20" long with a 0.030" thick non-taper-ground blade, the second 22" long with a 0.035" blade, also non-taper-ground. Both had nibs at the toe end, and solid (not split-nut) sawscrews, and a Warranted Superior medallion each. Handles are of 13/16" beech, nicely shaped on the handhold and with decent though not pronounced horns, and without lamb's tongues. The 20" has no stamps or etches, the 22" has a very faint stamp, "Buck and Ryan, London NW". I suspect that both saws are of 1920s or 1930s vintage - one reference I've seen suggests that the blade nib feature was dropped during WW2 (though there may have been exceptions to prove the rule!).

Both were toothed crosscut, 8tpi on the 22", and 6tpi on the 20". Both were in poor dental order, but the blades were beautifully straight. I've recut the 20" as a 10tpi crosscut, and refiled the 22" 8tpi as rip.

Testing both saws showed that they had no humps and bumps across the plate either flat or bent into a slow curve. So - probably not tensioned.

However, both saws now work very well, having little tendency to toe-end waggle in use. That's probably because they're relatively short, but nevertheless, it's hard to imagine what improvement tensioning them would make. It did cross my mind to get the hammers out, but since the blades are so nicely straight, it seemed daft to disturb them and risk introducing distortions.

Thus, I wonder whether 'tensioning' might be something that has some positive effect with longer flappier saws, but less with shorter ones like panel saws (unless they're very thin)?


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## Rhyolith (20 Apr 2016)

Wow, this is still going 

Thanks Corneel, think thats probably the most useful post so far in terms of getting to the bottom of this! Its also an example of the sort of thing this thread has been sorely lacking in in terms of proof. 

Personally I think it supports my theory (well not mine, just the one I believe is true) that "tensioning" in handsaws is a means of manipulating the internal stresses of a saw plate to achieve the same thing as a bow frame does (stretching the cutting edge). As that is how I imagine a metal plate to behave when bent if such a thing is done to it, the centre will have more compression and will be push out more steeply than the stretched outer sections (the cutting edge and back). The benefits of this are obvious *if its possible in a handsaw plate*, just use a bow saw with low blade tension -> then increase the tension and see for yourself! 

Warning! Sorta a Rant: I don't mean to offend anyone, but can people stop having a go at engineers/technical sorts, its wasting a lot of posts. Believe me I know how annoying it is when someone cannot see beyond proof and misses more instinctual aspects, but I don't think this is happening here. What is genuinely needed is just something beyond "this is what I think so there" as is demonstrated by Corneels post. Further, now I understand what the technical definition of stiffness is (its worth taking more than a few moments to think about it if your not an engineer or physicist) I agree with CC its probably nothing to do with saw tensioning.

Its seems that Lie-Nielsen still tension their brass back tenon saws, trying to get more info on this.


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## D_W (20 Apr 2016)

Rhyolith":1a59p3mq said:


> Warning! Sorta a Rant: I don't mean to offend anyone, but can people stop having a go at engineers/technical sorts, its wasting a lot of posts. Believe me I know how annoying it is when someone cannot see beyond proof and misses more instinctual aspects, but I don't think this is happening here. What is genuinely needed is just something beyond "this is what I think so there" as is demonstrated by Corneels post. Further, now I understand what the technical definition of stiffness is (its worth taking more than a few moments to think about it if your not an engineer or physicist) I agree with CC its probably nothing to do with saw tensioning.



That's me, and i'm not exempt from technical as I'm an applied mathematician. I started with the idea that there's probably a lot of scamminess in the past and low hanging fruit, but have learned to detach myself from the technical background and instead examine through the lens of continuous improvement over centuries. 

I don't have too many notions like this thread started with, that I suspect something strongly about a specific topic I don't have much experience with. I learned to drop that because the probability that you'll learn why you're wrong is pretty high. In this case, as with many others, embedded is the assumption that you are enlightened and hundreds of thousands of others in the past were stupid and easily fooled. Not just general population (you can certainly sell a butt jiggler exercise machine to thousands of unwashed), but professional users who didn't have a lot of spare cash. 

I don't see too much of this from non-engineers - it's just what I've seen in 10 years, and I started out on the other side of it. The notion that other people are responsible for providing the unwashed information for a foregone conclusion is also goofy. The burden is on them.

Plus, in this case, it has always occurred that the high end saws that I have, that have *more* taper (and less cross section because of it), have been stiffer without being harder to the file. It is an extremely easy thing to test. All one has to do is take a saw and do something demanding (cut something like beech 12/4 or 16/4 or resaw something of hardwood) with it and the wheat separates from the chaff quickly.


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## CStanford (20 Apr 2016)

Well said.


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## Rhyolith (20 Apr 2016)

Again, I don't me to offend you (or anyone else) this is just what I think based on my understanding of whats been written.



D_W":21qq9i33 said:


> That's me, and i'm not exempt from technical as I'm an applied mathematician. I started with the idea that there's probably a lot of scamminess in the past and low hanging fruit, but have learned to detach myself from the technical background and instead examine through the lens of continuous improvement over centuries.



So are you saying that we should be willing to look at this through a more subjective lens? 



D_W":21qq9i33 said:


> I don't have too many notions like this thread started with, that I suspect something strongly about a specific topic I don't have much experience with. I learned to drop that because the probability that you'll learn why you're wrong is pretty high. In this case, as with many others, embedded is the assumption that you are enlightened and hundreds of thousands of others in the past were stupid and easily fooled. Not just general population (you can certainly sell a butt jiggler exercise machine to thousands of unwashed), but professional users who didn't have a lot of spare cash.



If you could magic up a early 20th century saw doctor I would take his/her word as law on this topic, but the fact is we don't have any *reliable* evidence from that group, technical or otherwise. Regardless of the expertise of the people of that time (which I have a high opinion of) the fact is that the information they have left (that we know of so far) is uselessly vague, to the point where even knowing for sure if saw tensioning actually exists in handsaws is very much questionable. 



D_W":21qq9i33 said:


> I don't see too much of this from non-engineers - it's just what I've seen in 10 years, and I started out on the other side of it. The notion that other people are responsible for providing the unwashed information for a foregone conclusion is also goofy. The burden is on them.



I don't really get this point.



D_W":21qq9i33 said:


> Plus, in this case, it has always occurred that the high end saws that I have, that have *more* taper (and less cross section because of it), have been stiffer without being harder to the file. It is an extremely easy thing to test. All one has to do is take a saw and do something demanding (cut something like beech 12/4 or 16/4 or resaw something of hardwood) with it and the wheat separates from the chaff quickly.



I would gladly take the use of a tensioned saw vs a un-tensioned saw -> how they feel, operate and perform as evidence of tensionings benefit... but this relies on *knowing * a saw is tensioned in the first place. I have a number of old and new saws, and have no idea which are tensioned or indeed if any are. It takes a proper test or some solid non-subjective knowledge to find this out, mainly: what is saw tensioning?/how do you test for it? Which for me brings us back round to what I think CC has been after (I think!), which is *proof/evidence* that is to *vague and subjective*.


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## Rhyolith (20 Apr 2016)

CStanford":3pdiw97m said:


> Well said.


Who?


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## D_W (20 Apr 2016)

Rhyolith":1asqnjhh said:


> Again, I don't me to offend you (or anyone else) this is just what I think based on my understanding of whats been written.
> 
> 
> 
> ...



re: the tensioning thing. We're all operating from some area of lack of knowledge about it here. I don't think there is a 20th century saw doctor we can go to, those folks would've been feeding saws through rollers, though maybe I'm being errant, and perhaps that was done as a matter of skilled inspection and working something until it was as needed. 

With respect to subjective or not, subjective isn't really the right notion, more full research and understanding of a problem before coming to a conclusion or even significant bias. The probability that you're going to come to the right answer is increased by a whole lot when you learn more about the problem to begin with. Perhaps the right answer won't ever materialize because of lack of being able to understand the problem, and that's OK. "I don't know" is perfectly fine, or "i suspect, and that's as far as I can go". In a case like this one where someone proposing a hypothesis can't notice the difference between better saws and lesser saws (perhaps due to lack of really heavy actual use), then there's a real problem in drawing any conclusions at the outset. Especially if plenty of other people with more experience suggest a tangible difference. 

I would assume that engineers are left at work to either take a problem and come up with an engineering solution, or given the assignment to find problems and then formulate solutions and come to a conclusion. I would assume that has a lot to do with this being a trait of engineers, to assert something without having a full grasp on the problem to begin with. Most other professions aren't charged with as much analysis or problem solving, which probably limits the desire to do this kind of thing.


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## D_W (20 Apr 2016)

By the way, we have a problem of sorts in guessing which saws were tensioned and which weren't, and at least Kees is giving us some clues to start with.

The problem is even if a saw that we think wasn't tensioned is floppy, we don't know that it was floppy at manufacture, or if something happened to it. It's likely it was probably floppy at manufacture if it's not been rusted and it behaves normally under a file. But for any of us to stick our neck out and put a flag in the ground and say "it is written from here forward"....I'm willing to say I'm not sure but the evidence points to there being something to it a lot more than I'm willing to not understand the circumstances fully and put that flag in the ground.


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## Rhyolith (20 Apr 2016)

I still don't think I am grasping your issue with the engineers... anyway 

I think I know what saw tensioning is now, my theory is already described. Looking at this the other way round -> I cannot see why this wouldn't work, its just a case of it being possible to internally stress steel plates in the way I described before... everything falls into place for me then and my questions are answered/answerable through simple follow up logic. 

If that theory is correct then stiffening is nothing to do with saw tensioning, which using what I have learnt here, makes sense.


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## D_W (20 Apr 2016)

Rhyolith":1kzlwpey said:


> I still don't think I am grasping your issue with the engineers... anyway
> 
> I think I know what saw tensioning is now, my theory is already described. Looking at this the other way round -> I cannot see why this wouldn't work, its just a case of it being possible to internally stress steel plates in the way I described before... everything falls into place for me then and my questions are answered/answerable through simple follow up logic.
> 
> If that theory is correct then stiffening is nothing to do with saw tensioning, which using what I have learnt here, makes sense.



It's certainly possible that the saws that are properly tensioned return to zero faster and with better frequency, and it creates the perception of stiffness rather than actual stiffness. Who knows?

There seems to be a property in the better saws that when you put them into actual heavy use, they do better at it, and it's not plate thickness (as the cheap saws have thick plates without much taper).

(It's not only engineers who do what I described, and it's not all engineers - kees does quite a bit of looking before he comes up with a conclusion and states it. I mention engineers because it seems there is a professional tie-in to wanting to define a problem and then suggest a solution and reason through it. Why engineers? No clue, it's not physicians - they never seem to have the extra time, and they're also closely related to waiting for the results in terms of modern medicine in the states. It's not folks in the arts or humanities, they don't usually have the same desire to solve problems and be analytical. It usually seems to be engineers, or in one case recently, someone who has a quasi-technical profession that led them to believe they had drawn a firm conclusion because they could put errant data into a software package and declare they had a statistically significant solution). 

Other "engineered" conclusions that I've seen:
* steel was substandard
* old cap irons are inferior to new ones (most people don't even know how to use them)
* thicker iron is always better, thin ones chatter
* newer irons are harder, they're better because of that
* if craftsmen had access to lie nielsen planes, they'd have preferred them over stanley (probably not, the price would've been higher - stanley couldn't even get people to spring for bedrocks)
* new chisels are better than old chisels because of better steel alloys
* old saw steel was not as good as new saw steel
* modern sharpening stones are one of the greatest improvements in sharpening tools (never mind the fact that similar stones were available in the early 1900s at a price equivalent to a mid grade arkansas stone, but they never sold---alumina abrasive and resin binder and all.)

It's uncommon for someone to step back and say "why are older irons softer than new hocks" without knee-jerking "because newer irons are better", and the same for the rest of those. The errant conclusion that people were uninformed in the past, easily taken advantage of, and "we know better" now. Certainly that's true for something like a tobacco enema, but beautifully made old chisels were made the way they were because professional users preferred them that way. Same for most of the rest of the stuff. An educated pool of users found no preference for harder irons or thicker irons (God knows Ohio Tool tried to sell thick irons for a long time). 

We have pretty far to go finding out why things were the way they were, in general, rather than concluding they were antiquated junk.


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## Corneel (21 Apr 2016)

In this video from 6:50 onwards, Rob Steeper explains his ideas about saw plate tensioning.

https://www.youtube.com/watch?v=HITnU5m1eGo&feature=youtu.be


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## MIGNAL (22 Apr 2016)

Hmm. What's he saying, that it alters the resonant frequency? we could be getting into nodes and all manner of other things. Where's a bridge engineer when you need one.


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## pedder (22 Apr 2016)

Isn't he saying, it doesn't make the saw stiffer? 
(hammer) (hammer) (hammer) (hammer) (hammer) (hammer) (hammer) 

Cheers 
Pedder


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## MIGNAL (22 Apr 2016)

Yes but I think he's also saying that it has an effect on the 'wobble'. So if it isn't stiffer it must mean that it alters the way the whole saw plate responds to vibration/ chatter - call it what you will. 
I'm making a lot of this up. I'm not scientific enough to be able to understand or explain this stuff.


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## Rhyolith (22 Apr 2016)

Just watched the video. 

That does looks like altering the internal structure & stresses in the steel to me. It would be good to see him actually doing what he described.

edit: Just found this, don't think its been posted yet: http://mypeculiarnature.blogspot.co.uk/ ... nsion.html


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## Cheshirechappie (22 Apr 2016)

We clearly need an engineering solution to analyse this problem. I propose that we design a wobble-ometer to attach to the toe-end of saws in use. In order to do this, we need some funding, so we could apply for a research grant, asking for funds to analyse handsaw toe-end wobble with special reference to it's effect on climate change and it's contribution to world peace (because we could do with a bit of that round here) - we'd be bound to get extra cash if we phrase it that way. Then we could investigate the vibration of saws, maybe using different forms of damping to see whether tensioning was as effective as (say) putting a bucket of water under the toe-end of the saw, or sticking a lump of chewing-gum to the toe-end of the saw to stop it flapping around. Once the research information had been collated, the design and development programme for the wobble-ometer could go ahead, and manufacture arranged. With luck, the whole lot could be done to allow a release to market on 1st April 2017, allowing hand-tool users to check their saws for toe-end wobble.

Alternatively, we could do as Mignal suggested earlier; wait until Rob Streeper (or somebody else) has done a bit more work, then pass two otherwise identical saws, one tensioned and one not, to a few competent woodworkers and ask, "What do you reckon to these, chaps?"


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## D_W (22 Apr 2016)

I don't have any confidence that Rob Streeper is going to figure it out. I have had too many arguments with him about some saws being mid 60s hardness (which he believed to be true). 

If you want to learn about tensioning saws, you have a small window of time to make friends with a japanese sawmaker who still scrapes and hammers saws by hand. Nobody else is doing it professionally, and they have been trained based on incremental improvement, not educated or uneducated guessing and hoping.


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## Cheshirechappie (22 Apr 2016)

Just a semi-formed thought about what's happening.

Corneel's photos above show that when a 'tensioned' saw blade is flat, it is flat across it's width, but when bent into a slow curve, it starts to develop a couple of humps across the blade. Not very pronounced humps, but humps nonetheless.

A piece of flat sheet steel bends fairly readily. A piece of corrugated iron (made from the same thickness of steel as the flat piece) bends just as readily longitudinally, but not at all easily 'across the grain' of the corrugations.

The 'tensioned' saw blade when bent starts to develop humps like corrugated iron - so, the more it's bent, and the more pronounced the humps get, the less it likes it, and the keener it is to return to flat. Once it's flat again - no corrugations.

Not sure I've explained that very well, mainly because I haven't really worked out what's going on and why. However, it's a sort of 'working idea in progress' - thinking aloud, if you like.


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## AndyT (5 Jun 2016)

Excuse me resurrecting such a long thread without reading every word of it again, but I think I have a new bit of information to add.
One of the many pleasures of attending Richard Arnold's charity do on Saturday was the chance to meet sawmaker Shane Skelton, try one of his saws, and hear him talk about how he makes his saws, which are both modern and thoroughly traditional at the same time. He may well be the only sawmaker in Britain who hand tensions his saws, by hammering with a sawmaker's hammer.

It's not just a gimmick, he has made a thorough study of old techniques and explored how to apply them to currently available steel. The panel saw he showed us is closely modelled on a surviving eighteenth century original in the Seaton Chest.

Shane described the effect of tensioning as making the saw stiffer without removing its ability to flex and spring back.

The saw in question did seem to have a magical ability to cut in a straight line, no matter whose hand was on the end of it.

You can read a bit more about it here - scroll down to find the 26" panel saw.

http://skeltonsaws.co.uk/our-products/


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## Rhyolith (6 Jun 2016)

This looks familar, think I sent an email to them while trying to get more info on this. Never got a reply.

Was there any more detail on how the tensioing is performed?


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## AndyT (6 Jun 2016)

He said he hammered a line along the whole length, about an inch back from the teeth. He also said that there was a lot of work to get the taper grinding right with the saw straight and free of blemishes (which it certainly was.)


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## AndyT (9 Jun 2016)

Fortunately for those not able to be there, Jim was there with his phone on video mode and caught most of a long conversation between expert saw maker Shane Skelton and expert saw user Richard Maguire.
You can watch it here https://youtu.be/8NImt7g5iOQ - go to about 7 minutes in for the discussion of tensioning.

(There's a bonus if you watch to the end - Shane's plausible explanation for the nib on a saw!)


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## Corneel (9 Jun 2016)

I wish I could understand him! Especially in the part about tensioning, the sound quality isn't great, and that combined with the accent...


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## swagman (10 Jun 2016)

Cheap as chips Corneel. You could purchase the Skelton 26" Handsaw & the Skelton 26" Panel as a pair for the low price of  (euro) $ 1113.20 + shipping. #-o


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## Corneel (10 Jun 2016)

This is one of those rare instances where I would be inclined to buy a boutique tool. If I had the money. I think this is a rather special job, really worth something, and I can't make it myself.

Luckilly for a poor sod like me, there are still plenty of fine antique saws available.


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## D_W (11 Jun 2016)

I'd be inclined to try to make a saw like that for myself, but aside from that, I'd probably expect to get paid that were I making it and as is implied, it has the qualities that we are discussing about tensioning (staying centered well, stiffer , etc). 

Of course, such performance is available in old saws readily found here in the states, they just generally aren't as pretty.

I always figured (keeping in mind that I have no interest in selling try planes), that were I to make try planes professionally (with a few more iterations), I would expect about $500-$550 for one with a double iron. I have never sold one for more than $100, though (the cost of materials). It is just the reality of making tools unsubsidized, to make something so nice, it will not be $150 (the saw, or a long plane like any of the current good makers are making).


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