Re: [ATM] Ultrathin Project update

[Richard <cnc@cncservo.co.uk>]

Hi vorblesnak,

Wednesday, May 16, 2007, 3:00:11 PM, you wrote:

vpo> I have exhausted the ideas and rigs to make a sub-diameter lap work.

Just before you give up David...

I've been giving this some thought. If the convex side sat in
something infinitely rigid that conformed exactly to the convex surface
then there wouldn't be a problem, agreed?

How can we approach that?. The one thing that came to mind was setting
the convex side in fine plaster in such a way that there is no stress
on the mirror once the plaster sets. Once it has set, the mirror is
then pretty well supported against polishing pressure. It may be that
you would have to fill the concave side of the mirror with plaster at
the same time to keep mass balance and thus avoid stress during
setting. Maybe a fine tripod stops the mirror sinking totally and a
fine spray of mold release on the mirror stops the plaster sticking to
the mirror. If you could put the whole assembly in a vacuum chamber
after pouring it would help the structure of the plaster a lot. Zero
bubbles are left in the set plaster. Ask a jeweler what type of
plaster they use for centrifugal casting of gold rings - that gets the
vacuum treatment so the fine detail isn't lost.

You'd end up with a near perfect support for you mirror for polishing
which must spread the load about as well as possible. Heck, maybe you
can even lap it in with a few wets if it needs it. Maybe the balancing
lump that forms in the concave side can be used for your lap.

Lot of maybes there, but it could be food for thought, if you haven't
already tasted it.

-- 

Best regards,
  Richard in the UK

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