[ATM] Ultrathin Project update

[vorblesnak@peak.org]

I created a support using a piece of 1 inch rigid foam.  I cut a circle
with a diameter of 15 inches out of the middle so that what I ended up
with is a ring of foam, outer diameter 17 inches, inner diameter 15
inches.  I used foam core tape to act as stops around the perimeter and
laid the 15.5 on to the foam.

Three 20 minute wets later and much of the roughness of the middle of the
mirror had disappeared.  Still using the sub-diameter lap, long wide
strokes.  Three more 20 minute wets and I see an odd zone appearing at
about 80%.  It is as though I have polished in a hump at the edge. 
Probably the leading edge of the lap digging in as it hits the supported
section of the glass.  I also have just a hint of astigmatism started.

I have exhausted the ideas and rigs to make a sub-diameter lap work.  I
like the lightness of the lap and the low impact.  Controlling the mirror
has been a trial from day one.  Regardless of how I tried to support it
the supports pressed through and affected the front.  I will now make a
full sized lap and work mirror on top.

I ran some caliper tests on the glass, the average thickness is just over
9/64ths at this point.

David Davis
Toledo, OR 97391



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