re: cutting mirrors

On the subject of cutting glass, I'm not sure if anyone has mentioned
stained glass routers. These are diamond covered cylinders, about 1"
diameter, with a 1/4" bore and setscrew. They are used by stained glass
artists to smooth the edges of pieces and refine contours. With the axis of
rotation vertical, they usually sit in a little puddle of water and spin a
couple thousand rpm. This can easily be rigged with a drill press. The
coarse grit ones are quite agressive.

I usually mount the stained glass router like a tool post grinder and drip
water on it while the glass is slowly turning in the lathe.

BTW, the grinding of the edge of a lens or mirror to size is called
"edging".

In precision optics there are special machines for this purpose called
edgers, which by grinding the edge of the lens locate the center of the
optical axis to the mechanical axis to rather tight tolerances. OD
tolerance of less than .001" is not uncommon.

For reasons of thermal expansion it is usual not to put a lens (glass) into
a metal barrel with a tight fit. Most glass/metal CTE combinations don't
work out well. There are a few useful exceptions.

Elliot Burke