[ATM] Re: Stabilizing plate glass

["Mike Conran" <mike@guidesys.com>]

My experience with plate glass mirrors centers around a 16 x 1 inch F/4 
primary.

I would get measurements thru the day in testing that would vary from 1/3 
wave to 1/22nd wave!  My experience with it tells me that the material is 
really too dynamic in its expansion properties to make really seriously 
accurate and stable figures, at least that is my experience with it. 

Mike Conron 

Ken Hunter writes: 

> Julio... 
> 
> Plate glass is so temperature sensitive that
> essentially no one wants to invest the time into
> putting a flat surface onto one because the end result
> is an uncertain surface unless you are going to keep
> them in a controlled environment. 
> 
> You would not want to use a plate glass "flat" to test
> a pyrex mirror for instance. In industry, the tool
> (flat in this case) MUST be better than the part being
> measured. 
> 
> Ken Hunter 
> 
> 
> --- Julio Sanchez <jsanchez@skipanon.com> wrote: 
> 
>> Hi all, happy new year.
>> I have a few plate glass blanks laying around and
>> was thinking of making a
>> set of optical flats out of them. In the past I have
>> noticed that it takes
>> up to 24 hours for the plate glass to stabilize
>> after polishing or figuring.
>> In other words, you polish for 10 minutes and then
>> wait 24 hours to see what
>> you have. Recently I read on this board that placing
>> the plate glass blank
>> in water makes it stabilize in about 30 minutes. Has
>> anyone had experience
>> with this or any other way of stabilizing plate
>> glass blanks?
>> Regards,
>> Julio 
>> 
>> 
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Mike Conron 
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