[stephend]

When I hand-ground a mirror once upon a time, it wasn't too difficult, but that was a 6" mirror. I want to make a machine to grind a 20" mirror.

If I remember rightly, I circled the circular bench every 10 mins or so (motion A), and each back and forward stroke took say two seconds (motion B).

Motion (A) just repositioned the stroke, and motion (B) did the work. To make a motorised machine to do something similar would be fairly easy.

Would a two motor machine be better? One motor rotates the mirror blank (A), a second one moves the tool back and forth (B).

In this case, could (A) be much faster, say 10 rpm, and contribute most of the energy needed. And could (B) therefore be a much shorter stroke, because the blank is turning under it? In fact, could the tool driven by (B) be much smaller than the mirror blank?

I think having two motors should make it easier to avoid patterns and keep the natural randomness of hand grinding. Any comments much appreciated.