Re: ATM Question re: How long a figuring session

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

Ken,

Here is why I think the 10.5" may be too large for "linear strokes offset to
one side" on a 21" mirror.

The black circle is the 21" mirror, white circle is the lap, violet circle
is the 70% zone.  The groups of circles represent a single stroke.  The
yellow graph shows mirror wear for the given stroke.  These shots assume no
sideways variation, which would mitigate some of the worst effects:

Linear strokes on the 25% zone will pass the edge of the lap consistently
over the center of the mirror.  A hole will soon develop.  There's a very
nasty zone developing just outside the 70% zone, partly the result of no
side-to-side.  And the edge will seem to be turning, the result of falling
behind the rest of the mirror.

http://www.kupercontrols.com/misc/25pzone.jpg

Linear strokes on the 50% only barely touch the center of the mirror, which
will seem to rise up.  The edge is getting more than enough attention to be
thinking about turning -- the simulator doesn't model this, but it may
happen...

http://www.kupercontrols.com/misc/50pzone.jpg

Bottom line is that the "linear strokes offset to one side"  technique
requires a fairly small lap, say no more than 70% of radius.

Here's the "W" variation again.  Notice how the ripple and zones improve.
Whatever zones are there will at least be smooth and gradual:

http://www.kupercontrols.com/misc/lowright.jpg

Of course either of these techniques will tend to leave the edge behind.
The edge will seem to turn, by virtue of the rest of the mirror becoming a
comparatively shorter focal length.  Some intervention with (preferably) a
large lap will be needed to correct this towards the end of figuring.

Bill Tondreau