[ATM] 15.5 Ultrathin project

[vorblesnak@peak.org]

Just a brief update.  The holidays and such have kept me away from the
glass so it was nice to get them behind me.  I had finished with the
aluminum oxide and decided to jump into some polishing.  Other than make
and tune a lap I pressed into service an old 12.5 I had, with about the
same focal length.  A bit of heat, a bit of press and a new lap is born.

The problem is the glass is so thin I cannot polish with the mirror on the
bottom.  With the glass on top, after about 45 minutes of sporadic
polishing I appear to have a high center and edges that have not been
touched.  There is a lot of polishing left to do but I fear it is time for
a full sized lap.  Pooh! I say, POOOOOH!  I'll get over it.

The glass has a couple of minor zones but the lines are straightish, no
big wandering curves and no astigmatism, yet.  I also noticed reflection
from the back.  I defeated that last time by grinding the back, time to do
it again.

I will cast a disk of concrete and do the lap out of that.  I know I
talked about a wood lap but the drag between  glass and pitch moves the
whole mess around on each stroke.  That is why my polishing has been so
sporadic, I have been trying to get the lap to hold still.  Nothing to
bolt or clamp to on top of the washing machine.  I may be able to clean
the slumping and grinding tool and put the lap on top of that.  I will
have to look.  I will try and get a photo of the ronchi lines and post
them.

David Davis
Toledo, OR 97391

15.5 inch diameter
73 inch fl
11/64ths thick at the edge



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