Straightening a Custom Made Knife after Heat Treating

My Knife 34 came out of the quench with a small warp.

Here is how I fixed it. I’ve used this several times since and it has worked fine every time.

I clamped it to a solid straight piece of metal.

I tempered it at 450 degrees for 2 hours. The warp was slightly diminished but still there.

I added a finish nail behind the knife to provide a slight over bend and tempered for another cycle of 450 degrees for two more hours.

This time it came out straight.

Another option when Straightening a Custom Made Knife after Heat Treating is to use a leaf spring with the curve sill in it. Heat the knife and spring in the oven to tempering temperature and place the knife against the concave side of the piece of spring. apply a small (1″) C clamp to the blade and spring at the place where it warped and tighten till the blade is straight (ware gloves as everything will be hot) temper for 1-2 hours, cool, check and if not straight, do it again this time going a little past the straight point when you clamp.

Straightening Immediately After Quench. Immediately after hardening, while the blade is still warm to the touch, it is remarkably flexible. After a while that goes away and you have a hard, brittle blade.

Being prepared ahead of time with a couple lengths of angle iron in the vise, you can squeeze the knife back to straight. Jason Knight has a video showing how he does it with two pieces of 2 x 4. You only have a short period of time after the quench, so be ready ahead of time.

I’ve also used a leaf spring. The natural curve will sometime help with the over bend. Also keep in mind that additional tempering cycles when Straightening a Custom Made Knife after Heat Treating doesn’t have a whole lot of affect on the hardness.


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