From: "Bill T." 
To: atm{at}shore.net
Reply-To: "Bill T." 


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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