Re: [ATM] The 15.5 inch Ultrathin, more pictures

[GARY FUCHS <gary@rcn.com>]

Would it be possible to test the mirror horizontally with a flat 
above at 45 deg? This could shorten the floor space needed as 
well. 

Gary Fuchs

---- Original message ----
>Date: Fri, 21 Oct 2005 08:27:09 -0700 (PDT)
>From: vorblesnak@peak.org 
>Subject: Re: [ATM] The 15.5 inch Ultrathin, more pictures  
>To: "Ric Rokosz" <radicell2@yahoo.com>
>Cc: atm@atmlist.net
>
>> Very nice,but when you test the mirror given the
>> thinness,exactly how are you supporting the mirror on
>> the test stand?
>>
>> Ric
>>
>
>I have not really had a need to test on this mirror so far. 
Other than a
>basic spit test for focal length.  However, my test stand is very 
simple
>one. A vertical board with hole pairs drilled in it and short 
lengths of
>dowel. I can  move the dowels between holes to adjust for 
different
>mirrors.  It is like the bazillion other test stands built by ATM's 
over
>the years.
>
>The 16 inch showed no deformation when standing on edge on 
the stand. 
>That will be one of the bench marks on this mirror, will it stand 
and be
>tested, or will it fold and distort.  I think it will test.  The 
warping
>is a combination of shape and weight.  The 'shield' shape of 
the glass
>fights distortion.  The weight of the glass is very low, (I should 
weigh
>it, shouldn't I), I think it will test fine.
>
>The one concern I have is shaping the pitch lap.  For polishing 
I will
>make a full sized lap.  That, and the polishing, both require 
pressure to
>be successful.  I am thinking of a simple stiffener of plaster 
for shaping
>the lap.  Or maybe a plaster copy of the mirror to shape the 
lap.  I have
>had success setting a garbage bag of lead shot on the back of 
the mirror
>while polishing.  This allows the weight to spread out uniformly 
over the
>back but not pinch the glass.
>
>I am toying with the idea of a workshop on untrathin mirrors 
in Oregon. 
>Maybe in the spring.  Anybody here be interested in getting 
together and
>making a few 18 inch diameter by 1/4 inch thick mirrors?
>
>David Davis
>Toledo, OR 97391
>
>
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