How much pre HT grinding?

M

Mike22

Joined
Jul 27, 2015
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I'm still new to knife making more of a cobbler right now. But gotta start somewhere. I am going to be making my next few knives from 80crv2 some .125 an some .160 thick. I will also be using a 1x30 belt sander this time around instead of a jig and files. So my question is how far do you grind your blades before HT. Obviously when I used files I had to finish the bevels as much as possible pre HT. Thanks for the help.

Mike
 
There's no right answer. Using a grinder without variable speed I would want to get very close to finished to limit the amount of opportunity for over heating after heat treat. But it depends a lot on preference of the individual, the steel type and how it will be heat treated.

I generally try to get as close to finished as possible regardless of other considerations, because I don't find that doing more grinding after does me any good like eliminating warp, it'll just warp while you finish grind it. I only leave enough material to prevent the edge from wrinkling.
 
I go anywhere from hand finishing at 220 grit before HT to no bevel grinding before heat treat. As mentioned, different techniques for different situations. If I'm making a hand forged stick tang fighter, I'm going to keep my techniques in the vein of what the ABS teaches. That means after thermal cycling, I will grind the blade to mostly finished while keeping .020-.025" on the edge thickness, then I will austentize and temper the blade. If I'm making a folder, I will usually finish HT, surface grind the blade, then open and hone the pivot hole and set the lock and detent before I grind bevels at all. If the folder is W2 and I want a hamon, then I will rough grind but, leave plenty of flat so I can still finish the thickness on the surface grinder.

Bob
 
With oil quench steel I grind about 75% completed. This allows for any correction from the quench.

With air harden steels I grind anyhere from 90% to 100 pre heat treat
 
Are you doing your own HT in a forge? I use simple carbon steels 1084 and 15N20 stock removal with 1x30 and HT in my two brick forge by magnet and eye, quenching into canola oil. As kuraki said, I try to get it close enough without bacon edge after HT. Even bacon edge doesn't have to be a disaster if it can be ground down/straight, I just lose some height and/or width on the blade. Still better to avoid it, I don't even measure except by eyeballing it go/no go, LOL.

The main issue with a 1x30 is making sure not to overheat post HT and temper. If your 1x30 is similar to mine, the platen is tiny and you can easily overheat thin sections such as the tip. I basically grind wet with a spray bottle of water. After each pass, the blade gets dunked in water, then I spray down the belt and platen with water. Don't try to squeeze the most life out of your belts because an old crappy belt will more easily overheat the blade.
 
When was using a HF 1x30 and 1084 I was taking mine down to .010" a little thinner than the .015" - .020" I do now with a 3hp 2x72. You can't use a lot of pressure and the speed so I found just a little thinner and still had no warping or cracking issues. I do like the piece of mind I get now leaving them a little thicker, but I never had any issues going that thin when I was using it. Note: I did not make bucket loads of knives on the 1x30, around a dozen or so before I stepped up my grinder.
 
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