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Disc cutters / percussion tools


#1

G’day all; When a piece of steel rod is hit hard and frequently on
one end with a hammer, that end will distort sooner or later into a
mushroom shape; (usually sooner) the edges of that mushroom are work
hardened to the maximum quite quickly, and heavily work-hardened steel
becomes extremely brittle. In fact, just about every engineering shop
has several tales where the workers - especially the less experienced,
are injured by a bit of that metal flying off the tool with very great
force producing quite nasty injuries. My own son, many years ago had
to go to hospital with a piece of such shrapnel buried deeply into his
calf muscle; the doc had to cut quite deeply to remove it. (No, not
in my workshop. After he’d got his own, of course) Not a few people
have lost eyes that way, even through safety glasses - which are not
guaranteed bullet proof anyway.

So, the answer is simple; examine the hammered end of the tool each
time you pick it up to use. If there is the slightest bit of metal
spread over the edge, take it to the grindstone and grind a little
chamfer all round the edge, renewing it when necessary. That’s all -
except that it will probably be too hard to file off. – John Burgess;
@John_Burgess2 of Mapua Nelson NZ