Panel Saw Tensioning

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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.


In modern times, the blade material is hard rolled and heat treated at the steel works and so is supplied pre tensioned ready for blade production.

The old craftsmen skills have almost died. The exception is the "little mesters" that still survive and are often linked to museums.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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?
 
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?

No.

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.
 
woodbrains":u50rear1 said:
Cheshirechappie":u50rear1 said:
woodbrains":u50rear1 said:
Doesn't tempering, case hardening, annealing etc. vary stiffness without grossly changing thickness? Wouldn't stress hardening from hammering alter stiffness?

No.

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.

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.
 
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.
 
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.
 
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.
 
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.

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.

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.
 
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.
 
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.
 
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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