Panel Saw Tensioning

[D_W]

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.

 

[worn thumbs]

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.

 

[Cheshirechappie]

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?

 

[Cheshirechappie]

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.

 

[Cheshirechappie]

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.

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.

 

[Trafalgar]

I think you just described tensioning a saw.

 

[Cheshirechappie]

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

 

[D_W]

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.

 

[Cheshirechappie]

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.

 

[D_W]

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.

 

[Cheshirechappie]

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.

 

[D_W]

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.

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).

 

[D_W]

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.

 

[Cheshirechappie]

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.

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.

 

[D_W]

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.

 

[blackrodd]

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

 

[MIGNAL]

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.

 

[Cheshirechappie]

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?

 

[D_W]

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?

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.

 

[Cheshirechappie]

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.