How to straighten bent saw blades

[george wilson]

Glad it worked,Rob,you are lucky that the saw blade was loose enough at the front end to slip there the most. Had it slipped in the center,the blade would have ended up more wavy. Why don't you run a thin stream of Loctite down the juncture of blade and back? If it was prone to slipping,it could slip again.

[Rob Luter]

I may try that, or perhaps some CA glue. I wonder if that would prevent me from "adjusting" it again in the future if I need to? What's odd is that there are no perceptable "witness lines" that would indicate anything moved. I know it wouldn't need to move more than a few thou' to cause ripple, but I expected I'd see it.

[Joe Cunningham]

Thanks for sharing your expertise. I have a Disston backsaw with a slight wave in it, but I've not tried straightening it yet out of fear of making it worse, so it sits unused. Maybe I'll take a look this evening.

[george wilson]

I'd only recommend the least aggressive type of Loctite. Ca won't hold. Maybe only put a few inches near the tip of the saw. You could gently heat the back to make it let go later,but have the saw in the vise by the front edge of the blade first. The vise will be a heat sink to keep the blade safe. I have a saw just like yours. Probably as good a saw as you'll ever need.

DON'T try squeezing the back. It might end up springing it open,then you will have ruined the back. When we made ours,the empty backs were carefully adjusted till their gap was smaller than blade thickness. Then,the blades were tapped in. If we squeezed a back too hard,it would come all the way together at the folded line,and open like a clothes pin on the gap edge. The back must have a "horse shoe" shape to it,so it grips right along its gap. This is why I don't recommend sawing the groove in the back. No gripping power,must be glued to hold the blade. Mechanical grip is always better,and easier to adjust later.

[Bob Jones]

Gorge,
Can you give more detail on how to get a gradual curve out of a handsaw after you pour the boiling water over it? I just bought 2 old number 12 disstons and they both have a bow. I don't want to ruin them!
I tried bending them over and back in a circle. I didn't get to a full circle because of fear. Both blades went back just the way they were.

I like the oven idea. Seems less likely to scald myself. Thanks for the tips!

[Marv Werner]

I don't mean to be argumentative here but I have straightened hundreds of handsaw blades by merely bending them in the opposite direction. No hot water, no propane torches, no vegetable oil. Nothing tricky or mysterious about it.

The blade somehow got bent in the first place. Did it get bent while in hot water or hot vegetable oil? Probably not. Most likely it was bent when it was at room or ambient temperature.

A saw blade can be straightened in a pattern maker's vise, but not while clamping it tight. Leave the jaws open about an inch. When you bend the blade, make sure it is bent in an arc, pretty much as when it got bent in the first place.

A saw blade is spring steel. Coil springs are made from spring steel wire. Spring steel wire is bend when cold. I made many coil springs out of piano wire. A spring steel saw blade can also be bent cold.

Hammering dents or a sharp bends/kinks in a saw blade is possible, if done on an anvil or an other well supported surface. However, hammer blows should be done using a large face hammer with a slightly rounded face. The hammer should be 3 to 4 pounds. The weight of the hammer is about all that's needed to effect the tension that's right in the dent or kink. Don't expect to get the blade hammered to the extent that you no longer see the dent or kink. All you want to do with those kind of situations is to reduce any drag in the kerf that might occur. Just make it better with a few hammer blows. If you over work the metal, it can become brittle. Keep in mind, there is already lots of tension in the metal from previous tensioning, especially with the older saws.

Just bending a saw blade in a circle will not straighten it. The bending has to take place over a short distance right where the bend is. You must apply hand pressure right where the saw exits the vise jaws that are open about an inch while at the same time maintaining an arc, kind of like a smaller circle so to speak. That is usually how the bend occurred in the first place.

The saws I have straightened in this manner have not returned to their bent state over time as others have claimed they will.

[James Taglienti]

Thank you for this george

[george wilson]

Marv,he just said that back bending didn't work on these particular saws. Maybe he didn't bend them enough? It's possible. If he can't get the curve out of them,heating and bending WILL work.

The spring steel we used to make our saws is 1095. It came in coils. Old saws,who knows what spring steel they were made from? All I can know is ours are a LOT harder to file,and must be made of higher carbon steel.

Anyhow,it is obviously the FIRST thing that comes to mind to bend it the other way. I can promise you,that did absolutely nothing to get that slight curve out of the steel we used.

We tried localized bending too. It simply would not take the bend out of these blades.

I don't know if the spring steel was still hot when they coiled it or how long it was coiled from the factory. Factory steel processing often is continuous,and there is a lot of length in a standard 1500# coil of spring steel,so it needs to be rolled up to make it compact. Cold bending didn't work as it might on softer saws.

What did help was getting the blades hot. Then they straightened right up by bending them in the opposite direction. This was our real life experience with 1095 coiled spring steel @ 52 R.C..

I think I already related this at the beginning of this thread.

Bob,you can bend a decent saw blade all the way back till the tip touches the handle without fear of it breaking. A good old Disston certainly should not break. Done it many times. I'd just pour some boiling water over the blade,except for the last few inches at the tip. You should wear gloves,of course,to grasp the tip,and you NEVER want to get hot water on your gloves!! You can't get them off fast enough!!

You could just clamp some wood on the tip of the saw to take hold of. The blade will cool off fast,so do it quickly. That should solve your problem.

[Andrae Covington]

Happy to report that this worked pretty well for me. I had a saw that was curved out of line almost 1/4" at the toe. I had tried cold bending it but no luck. So I tried the boiling water out on the back porch. It worked so well I bent it too far the other way and had to bend it back, hah. The saw isn't perfectly straight, but it's a lot better than it was. I may try again and see if I can fix the slight kink near the toe.

[george wilson]

Good to see that you had good results,Andrae!! Endless debate is one ting,but actual real life experience is another. This is how we straightened that long workbench full of saws some might have seen pictures of.
And the ones we didn't bother to photograph.