Straightening a Saw Plate

[TraditionalToolworks]

The late Stephen Shepherd (R.I.P. 2018) in Full Chisel Blog also weighed in on this topic, I saved it as well, attached.  Glad I did.

Darn, thank you for that document. I have actually discussed this at length with him in the past, actually, I he was very helpful the first time I did French Polishing. It was articles that he had on his website at the time. He was the nicest guy in the world, did a number of antique repairs and was very knowledgeable about historical joinery.

It was actually Smalzer's article that created me to ponder about this. I know Stephen did use wood, but he had a lot of old stumps, I tried it and it didn't do anything for me. I've tried rawhide hammers, and softer wood heads, mallets, etc...but I never tried the flat of a small sledge.Not matter how you look at it, even by hitting it with a flat, you are still displacing metal. There is just no other way to look at it, most iron hammers are hardened more than the plate. Hitting it seems like forging cold steel. If you think about a metal spinning lathe, the tools deform and stretch the steel.

If you use heat, you should be prepared to reharden the saw.....

Yes, indeed. But we can temper with heat also. In a forge one would bring the metal to cherry red, dunk in oil, but then bring it back and light the oil and let it burn off, then bury it in ashes so that it cools as slow as possible. Then take it out an hour or two later, even the next day. Then check it with a file.

At least this is how I've done it and was taught, like for a knife blade using spring steel.

When we file we don't get it hot enough to loose the temper, but I was thinking it could control the tempering as well. If two heated hefty plates would press the saw plate, we know we can take it to about 2300 degrees, but it will be hard to do anything else with it at that point, if you can even find it. I've bruned a lot of things up in the forge with one too many cranks on the blower. Today there are heat treating ovens that you can program, so this is what got me to thinking about using heat. If we can take it up to melting point we should be able to control some point that will allow the sides to press against the saw plate. It's just an idea I have thought of, nothing more.

My experiments with peening and soft head hammers, and a rounding hammer is just that, experimenting. But I have only done experiments as I would just replace a saw plate, 1095 steel is cheap enough, and readily available. A saw maker should be able to straighten a place also, but replacing is a viable option and I can do that. Or just make another saw.

I wouldn't depend on heat to properly tension a saw plate.  For one, the heat is a temporary thing.  While it may seem straight when you've applied the heat, as soon as the plate cools, you're back to the original configuration.

Is this is so, the process wouldn't have been successful. And maybe you know something that I don't about metal, cause I don't have a degree, but if spring steel does spring back you haven't changed it and I would think it was not gotten hot enough. Heat it too much and it will melt into vapor after turning white. You can see it during the last couple seconds.

We have better digital controls these days, so I'm only saying that if one was to experiment with heat control it should be able to both anneal and re-temper the steel.

Is it worth trying? I don't know. Kinda similar with saw vises. Are we to continue using old heavy Disston 3D vises if we can find them? I do like mine, i use two of them. I just think that every time I pull one out to use I tend to tell myself, "darn, that's heavier than I remember". I think that has to do with age. LOL I believe magnets is the answer to that problem.

And similarly, speaking about vises, I prefer the import clone pattern maker's vise over the Emmert's which is just too big for most work I do, and this is exactly why the cast iron breaks, those are pretty heavy if you've never picked one up. I am using another import on my next bench.

[TGW]

The 28" Disston number 7 which I use at work (traditional carpentry part time) had a severe kink in the blade when I bought it for 50 cents. I hammered the blade straight and retensioned it following advice given by Bob smalser in an article and a chap on a forum who seemed to know a bit.
It worked and 15 years later I still use that saw. It cuts as straight as any saw.

Using heat to straighten steel implies heating aspot red heat and leting it cool and schrink. Woud destroy the temper of a sawblade and induce internal stresses whick probably would make it brittle.

[CStan]

Somehow tapping out a kink removes tension, but tapping elsewhere, in the exact same manner, restores tension.

Neat trick, no?

If in removing a kink, you get the kink out but the saw develops a slow uniform curve end-to-end in the process, then you have a problem with tension.  If you remove the kink, and it stays straight, don't hit it another bloody time.

It's fine.

A saw with a slow curve has too much "tension" on the concave side. Bend the tip until it touches the handle going the opposite way. Let it spring back sharply. You might have to do it a few times. It should straighten out. If it doesn't you might have to tap out the hollow side, around the middle of the saw, not to induce tension, but to release some and let the saw straighten back out.

Tension is not induced as much as it is equalized.

[bandit571]

I seem to recall another, less violent way to straighten out curved saw blades.....and was done be the folks at Disston, back in the day.....

Seems to involve the use of a heavy leather glove.    Brace the handle end up by your chin ( to sight done the plate) Brace the toe against a stop on the bench.   Gloved hand made into either a fist, or just use the palm of the gloved hand....Idea was to rub/run the hand down the length of the plate.    You are trying to push against the curved area, to work the plate back into Straight.   Usually was done right after they had filed the teeth.   At least according to the video I watched.    

Have used this trick a few times....usually on Yard Sale saws, that has sat way too long leaning against a wall, somewhere....instead of being hung up.


Any hammering I have done....ball pean hammer, with the plate on my wooden bench.....more of a "tap,tap,tap,tap....." than full blown banging.   All in the wrist.

YMMV

[adamcherubini]

But we can temper with heat also. In a forge one  would bring the metal to cherry red, dunk in oil, but then bring it back and light the oil and let it burn off, then bury it in ashes so that it cools as slow as possible. Then take it out an hour or two later, even the next day. Then check it with a file.

At least this is how I've done it and was taught, like for a knife blade using spring steel.

When we file we don't get it hot enough to loose the temper, but I was thinking it could control the tempering as well. If two heated hefty plates would press the saw plate, we know we can take it to about 2300 degrees, but it will be hard to do anything else with it at that point, if you can even find it. I've bruned a lot of things up in the forge with one too many cranks on the blower. Today there are heat treating ovens that you can program, so this is what got me to thinking about using heat. If we can take it up to melting point we should be able to control some point that will allow the sides to press against the saw plate. It's just an idea I have thought of, nothing more.

My experiments with peening and soft head hammers, and a rounding hammer is just that, experimenting. But I have only done experiments as I would just replace a saw plate, 1095 steel is cheap enough, and readily available. A saw maker should be able to straighten a place also, but replacing is a viable option and I can do that. Or just make another saw.

Huh?
To harden steel, you heat past the critical temp, then quench. All steels become non-magnetic at around 1350F. But 1350F is the critical temperature only for 1077 steel (.77% C). For both higher and lower carbon steels the critical temperatures are higher than that. For 1095, the critical temperature is roughly 1450F. These temps are beyond the reds and into the yellows.

What you wrote sounds like annealing except that cherry red isn't nearly hot enough. And the long soak at temp is annealing, not hardening or tempering.

To temper, you heat to a controlled and uniform temp. For a spring steel, that temper could be quite high. I think 600F is mid 50's Rc. I made chisels with tempers as low as 300-350F (mid 60's Rc), before settling on a 400F temper (approx 61Rc).

Here's what woodworkers need to know on this subject:

In theory, you could heat a saw up to its original temper temperature without changing its properties. And you're not liable to do that accidentally. I'm not sure what effect heating would have however. Japanese woodworkers seem to think (or have thought) leaving chisels to bake in the sun on a sunny day helped them. So maybe there is some normalization that occurs? Because I don't understand the metallurgy, doesn't mean they are wrong. But I think we are fairly safe about heating below the temper temp.

With chisels, the temper temps are much lower and you can easily reach those on a grinder with poor technique. A slight discoloration is your first clue. This typically happens at the edges where the heat is getting trapped. If you get a blue spot, that's really bad, typically over 550F. You've wrecked the temper in that spot and softened the steel. There is a Heat Affected Zone beyond the blue, which woodworkers hope to ignore away. And you can't polish away the blue to make the problem go away. The oxide color forms on the surface, but is bad all the way through. You should really grind the whole edge back + 1/32" at least (typically using the same grinder, crappy clogged wheel, and poor technique that created the problem).

Last: When I started woodworking, I was using my chisels alot (as you do). I searched for chisels that were wear resistant or super hard such that my work did not need to be interrupted by sharpening. I was using the scary mess technique because it was cheap, but made a mess and really was an interruption. I wrote on the internet about chisels I bought and returned or sold that I felt were too soft (e.g. Sorby). I was wrong. That was a rookie mistake. Better technique and better sharpening, brought longer edge life. I didn't need the uber steels. Developing sharpening methods I could integrate with my woodworking was probably the best thing I did for myself.

I know this is a saw straightening thread, but I guess I think its good for HT woodworkers to talk about steel more because its so essential to our work.

[bandit571]

This saw did have 2 curves in it's plate....DID

   

20oz smooth face hammer, and used the top of the bench leg as the "anvil"....


About 5 minutes of hammer work, checking after each hit..flip the saw as needed....seemed to straighten it right out..

   
Still need to stone the right side of them BIG Rip teeth..

   

26",  5-1/2 ppi, Nicholson USA.....teeth can indeed be re-sharpened..

   
$1 Yard sale find....might just come in handy.....inspite of the hanger hole in the toe

[TraditionalToolworks]

Nice work Bandit, looks like it's cutting straight enough for me!


I know I don't need to say, cause you're one of the people that will, but go build something now!

[CStan]

Here's a guy who doesn't get lost in too much theory:

https://www.youtube.com/watch?v=VrCiq2v30jo

A full-sized saw's cuts are dressed to the line with a plane.  You don't need a surgical instrument.

[TraditionalToolworks]

Here's a guy who doesn't get lost in too much theory:

https://www.youtube.com/watch?v=VrCiq2v30jo

A full-sized saw's cuts are dressed to the line with a plane.  You don't need a surgical instrument.

This method does work and I've used it in the past, but it's really dependent on the top of correction the plate needs and/or how it was bent.

This is way better than displacing metal with a peen, IMO, but that's probably subjective also.