Hand Tools Archive

Subject:
Separate Comment

David Weaver
I didn't really get much re: the specialty abrasives until recently getting a high speed belt. I figured something would be different at speed, but until getting hands on, I wouldn't have guessed the huge difference in performance that flip flops with speed.

For example, all of the abrasives, no matter what, break down fairly quickly. For heavy hand pressure, what you really want is a 1-2 combination of things that work well when partially broken in but that are tough. Plain non-fragmenting alumina meets this. 80 grit is a little brisk at first, but as it settles in, it works very well. 220 seems great at first, but once settled in, it's a little slow (but still a great set up for a stone).

Fracturing abrasives like pressure sensitive ceramics and silicon carbide break down very fast unless light pressure is used, but that's not generally what you want by hand. There's more accuracy with higher pressure and fewer strokes. They last less long than actual alumina and don't work faster because they go too fine too fast.

Flip things around on a belt grinder and the inexpensive aluminum oxide abrasives work OK, but generate a whole lot of heat. The ceramics that break down under hand pressure come into their own, and the particles that they remove are much larger, especially in annealed material, and in hardened material, they grind so cool that you can add bevels to a chisel after quench and temperature and not threaten tempering.

This kind of thing is poorly advised where there's no industrial precedent. There's none that I can think of for heavy hand grinding, which is what the first step is on any tool that's not flat enough to go directly from stones. Experience is king, and laziness combined with repetition (repetitive work is where laziness really flourishes due to the drive to do it faster and faster with less effort) beats textbook advice.

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