Hand Tools Archive

Subject:
Heat

David Weaver
A long OWT for japanese chisels has been absurdly low tempering temperatures and chance of ruin (in some cases, stan covington has mentioned career craftsmen in Japan who actually believe that synthetic stones lead to high end chisels that are suitable for nothing but the trash - as in, a small synthetic abrasive will permanently ruin a chisel through and through).

After the last trolling dust up here, a quick look at hitachi's tempering schedule shows White 1 starting around 325F (on the high end of hardness).

While that's below tempering colors, the idea that japanese chisels will go soft with the tiniest amount of power grinding is just factually incorrect. Perhaps there are softwoods in japan soft enough that extremely undertempered chisels will hold up, but there must be a lack of A/B testing to feed the idea that there is some advantage to overhard chisels.

As you say, same principles apply - grind short of the edge, continue on. When I refurbish new to me chisels, I will sometimes grind them off square, and then grind them to the edge or nearly to the edge when bringing the full bevel back to meet the squared edge. They may have one sharpening cycle of odd behavior (if they're really hard and the edge is fully ground off) and then it's gone.

If damage is prevented when using the chisels, then there's never a need with japanese chisels to grind again. I tempered an overhardened chisel a few weeks ago (terrible edge behavior, quite old, nobody ever fixed it) and then unicorned it and was going to post a video of the whole process, but I got so overzealous pushing the edge that the tang/handle joint couldn't handle the bashing. That's a chisel that was supposed "ruined" by tempering to 325 degrees. It was still ice hard on the stones.

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