I was grinding lathe bits today on my new grinding and sharpening mobile
platform. I had it parked in the garage doorway, facing west, so the light
would be better and the dust would blow out.
At one point I noticed a wisp of smoke coming out somwhere behind one of the
grinders. Now I may be overcautious but I consider smoke and grinders an
inherently undesirable combination.
I was puzzled: There was hardly any sparking, the bits were cool enough to
hold bare hand. No strange noises. I looked and there on the brand new top
was a burn - a linear scar, about 2 inches long, about 1/8" deep, about 1/4"
wide with deeply charred edges. What could have caused this?
I moved my head and it became clear: The sunlight hit the grinder shield
which has a lens in the middle. The lens was focussing the sunlight onto my
bench top and burning it, judging by the length of the scar for a quite a
while (for a sundialist it is tempting to calculate the exact time by
measuring the length of scar exactly and estimating the amount of Earth's
rotation from it but I am too lazy). Everytime I came to grind my head got
in the way of the sunlight and the bright focus of light would disappear,
leaving only the wisp of smoke as evidence of anything wrong. The burning
would start again when I left the station to do things elsewhere.
I am sure that there are lessons here somewhere...In my defense I should say
that we are not used to sunshine around here.
12 years ago