Re: [ATM] RE: Glued mirrors?

[Ric Rokosz <radicell2@yahoo.com>]

--- Jarvis Krumbein <jkoptic@juno.com> wrote:

> Before you charge off to do a mirror with a Hextek
> blank, you might want
> to check with John Vogt about "print through and
> astigmatism" problems. 
> John has done a couple of 32" Hextek mirrors which
> have been prize
> winners at Stellafane and spent a lot of time
> conquering the problems
> mentioned.
 
 The mirrors that Jean and I make (my technique is a
tad differenet than his ) have much thicker faceplate
and internal structures than the Hextek blanks that
negates the problem of astig being introduced onto the
blank during polishing.No doubt the Hextek mirrors are
a marvel of manufacturing technique,but tricky to work
and one has to be super aware of the potential problem
and take steps to counter the tendency.

The only time I've gotten one of my mirrors to produce
astig was when it was badly annealed.This only
happened once in the early experimental phase.Some of
the early Stabilite cellular blanks also had this
problem and drove Zambuto and Hall up the wall,not to
mention nearly out of business which is why they
switched to the 1.625 inch thick pyrex blanks which
also had problems with anneal/strain patterns in the
glass -which explains why some of us make our own
blanks.:)

Ric







		
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