ATM "Funny blank"

["David Harbour" <scarab2@cox.net>]

To all-

I hope I didn't miss an earlier suggestion, an earlier post along these
lines, but I am about 88% certain that the concentric rings found in certain
molded mirror blanks are for use as a sort of "reference grid", marks for
helping one position the mirror relative to the tool more accurately in
terms of degree of offset and or stroke length, and visualizing where the
center of the mirror is a little more accurately, etc. They would be
particularly helpful when needing to draw an additional circle on the back
of the mirror for guiding it more accurately when treating a specific zone
on the mirror with the edge of a full sized tool.

Everyone does this, don't they? Draw circles on the backs of their mirrors,
I mean? (Oops- I hope... uh...)

I long ago starting marking the backs of mirrors that I figured, with rings,
a dot for the center, radial index line for counting full and fractional
rotations, etc. The backs of my mirrors kind of looked like maps of the
world, sometimes. To a great extent, in "the old days", the method of the
full sized tool was mostly mirror on top for figuring, and anything that
made it handier to know more accurately where the edge of the tool was
coming to relative to the mirror was useful.

These rings, if they are accurately made, can serve to help see the edge of
the tool be consistently offset, during stroking, by a specific amount, or,
they can also be used to help see the edge of the tool come to the same
degree of length of stroke. Helping visualize where one is more accurately
during stroking couldn't hurt, I think.

Of course, I might be full of you-know-what. But the only trouble I EVER HAD
in figuring was you-know-what. So, as regards nice concentric rings on the
back of a mirror blank, well: "works for me". (Worked, past tense: can't
push glass anymore)-

Davey