Re: ATM Mirror making machine question

["Bill T." <twentiethwave@hotmail.com>]

I've used figuring techniques that stroke-dominant (more than one stroke per 
table rotation) and rotation dominant(more than one table rotation per 
stroke).

Of the two, I greatly prefer stroke-dominant for figuring, which is what you 
have now.  In my particular experience this gives much nicer edges, since it 
concentrates most of the work at the mirror center -- basically it allows a 
relaxed "dig out the center" approach to figuring.  When table rotation is 
fast compared to the stroke, the edge of the mirror gets worked a lot 
faster, and is more vulnerable to turning.  However, nothing can polish out 
a mirror faster or better than a rotation-dominant machine.

An exact 2.25 strokes per 1 turn stroke, or any stroke that exactly repeats 
over a short time, can produce a very ripply mirror.  It's best if you 
select a ratio that has a very long period between repeats.  If you attach a 
marker to the lap holder, a machine with a good ratio would very quickly 
scribble over a cardboard mirror stand-in, without creating an asterisk-like 
pattern with untouched white spaces.  In a fairly short time the entire disc 
should be filled in.  Less than perfect is ok, as long as there aren't any 
pronounced, un-filled white spaces after a minute or two.  If you don't have 
a good coverage patttern, just changing one pulley can help a lot.  The 
adjustable drive pulleys used for swamp coolers in the Southwest are very 
handy for ratio tweaking.  It's possible that just going to a smaller or 
larger thickness belt could also help, without chaning pulleys.

Bill T.






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