Cutting torch for material removal

H

H20MOFO

Joined
Apr 20, 2016
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I am just wrapping up my first knife. My second one is gonna be from a piece of 1/4" 5160.
I am getting NO where fast with a sawzall. Is there any metallurgical reason a falla shouldnt use a cutting torch??
 
Ah, you've learned that Sawzall was inappropriately named. ;)

First, 1/4" stock is pretty beefy... does your blade really need that much?

Second, a metal cutting bandsaw would be preferable to a cutting torch, because the torch will leave a heat affected zone on the knife that a proper metal cutting bandsaw would not.
 
I am making kind of a mini kukari chopper...wanted 1/4" If I had a band saw I wouldnt be using a sawzall.
Soooooooo you are saying that it WILL cause metallurgy issue???
 
Short of a metal-cutting bandsaw, I would just use an angle grinder with a cut-off disc, or cut out the rough shape with the torch a little oversize and grind away the heat affected areas.
 
We use a torch on saw mill blades cutting knives out almost every day, but cut over size and grind to finial size. Blades are then normalized, ground, then hardened & tempered. Would use a band saw but saw blades are too big and hardened.

 
There's nothing wrong with using a torch if you do like Don does and leave yourself stock to grind away. You're going to have two layers to deal with at the edge of the cut. The heat affected zone is one, and the layer of slag and decarb is the other. Don's picture is an excellent example of how to do it right. In the bottom right corner you can clearly see on the edge of the plate the heat affected zone is minimal, and all his cuts are rather smooth.

The danger with a torch is cutting to slow. Too much heat and oxygen for too long in a single place is A Bad Thing™ just like it is in your forge or furnace. But a properly set up torch or plasma cutter, especially in the thickness materials we work with, moving at the proper feedrate will keep the area you need to remove from grinding minimal. It isn't the heat affected zone you have to remove, it's the slag and decarb that is no longer steel. The heat affected zone is simply tempered, and can be brought back to full hardness.

If you're good with a torch, cut out your profile an 1/8" big all the way around and grind it back. If you're not good with a torch, make a template to trace (although a suitable template for torch cutting has similar issues to make that you are experiencing with your knife blank).
 
Yah, sorry that's what I meant by "heat affected areas"...just all the slag and decarb. That's the only bit that was truly negatively affected by the torch.
 
Don,
How much do you grind away when you torch cut the profiles of the blades to get to the good metal?
Thanks,
Doug
Jn. 3:16
 
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