Re: ATM Be very careful

["Russell Jocoy" <russjocoy@hotmail.com>]

>From: "Vladimir Galogaza" <vladimir.galogaza@zg.tel.hr>
>Reply-To: "Vladimir Galogaza" <vladimir.galogaza@zg.tel.hr>
>To: "ATM shore" <atm@shore.net>
>Subject: Re: ATM Be very careful
>Date: Thu, 28 Aug 2003 19:43:33 +0200
>
>
>Re Frank's experience,
>
>Some facts should be mentioned repeatedly from time to time. One of those
>facts
>is that we should treat the mirror as it is made of rubber. At orders of
>magnitude we are working ( parts of wavelengths)
>and at forces applied, flexures are inevitable and considerable.
>There was very instructive mail from our friend Ulhas ( I think, or was it
>Stathis?),
>with central hill on his mirror, and rather stubborn one. He put a circular
>  thin sheet of paper underneath the center  and soon hill disappeared.
>This "Princess on pea" effect is basically the same as one Frank  described
>as  consequence of the unsupported edge. Ulhas cleverly took advantage
>of it. and Frank found out it soon enough to avoid  trouble.
>
>Frank's well described experience will certainly have positive impact in
>stressing importance of proper mirror support.
>
>One remark in addition.
>It will be helpful for archives search if subject title will reflect the
>contents as
>descriptive as possible. In this case "unsupported edge effect on 
>polishing"
>  will perhaps be more appropriate ( in the long run)  than " Be very
>careful".
>
>Vladimir.
>
>
>
>
>
>
>


("atm@shore.net")

    Vladimir,   You make some important points on grinding and or polishing. 
   I tend to adhere to
the theory that glass should be supported at all points during grinding and 
polishing when the tool
is on top..... What happens when the mirror is placed on top of the tool,  
Does the tool flex, No...
Does the surface below the tool flex?..Yes if the surface is glass friendly 
(I mean ready for the glass
to flex)   I am directing this statement to the "thin" glass pusher. I have 
grinded, polished and am
now figuring my 5/8" x 9.5" glass,   never having it come off the table... 
Tool on top the whole way..
      This is not a traditional way of creating a mirror but I am real close 
to the end.  It's not that I don't
like the process of the flip back and forth,... It's the fear that if I put 
this thin glass on top of the mirror
I will bend it and create deviations in the surface.....  Thus I have had my 
glass supported as if it was
floating.. Initial rough grinding was done with a wet thick carpet.... The 
finer stages with the flexable
cabinet liners, and the same with polishing...  This process can be done 
tool on top all the way...
    But as you have made clear support is the KEY to the end result,... just 
as it is in the scope mount.
  Uniform support during grinding or figureing are critical even if you are 
going from top to bottom.
    Thus the end result needs the same respect of support...    Just my 
thoughts... Have you ever done
a mirror all the way on the table?......    Russ Jocoy
("atm@shore.net")
>

_________________________________________________________________
MSN 8: Get 6 months for $9.95/month http://join.msn.com/?page=dept/dialup