Re: [ATM] Newbie needs help getting to sphere...

[John Lynch <john_lynch2006@yahoo.com>]

Graham,

I found it helpful when I rough ground a 6" mirror to
watch the bubble pattern to see where contact was not
being made.  Of course, this was at the point when I
had completed the chordal strokes and was basically
grinding center-over-center or close to it.  At that
point, the mirror was not spherical, but actually a
rough outline of one.  I then redistributed the coarse
abrasive with my fingers to those areas that were
making good contact and continued grinding with
shorter strokes until the bubble pattern got smaller. 
Remember that you're going to begin dealing with
differences that are smaller than the #80 grain size,
so that would be the time to switch to #120, i.e.,
you'll only continue to grind off more glass and not
make any progress toward a smoother surface.

Good luck!

John Lynch

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