Re: [ATM] Large Thin Mirror

["Bob May" <rmay@nethere.com>]

Plop probably assumes that the glass is laying on the support
points without any lateral support.  I guess that the proper way
for ultralightweight mirrors is so glue the support points onto
the back of the glass and support the lateral stress that way.
I'll note from my previous post that you can and will get several
waves of error depending upon how you support the glass in
polishing and testing so you do need to pay good attention to
that little problem.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net

----- Original Message -----
From: Ted Cohen <tcohen@blakeglobal.com>
To: <atm@atmlist.net>
Sent: Friday, May 09, 2008 4:07 PM
Subject: Re: [ATM] Large Thin Mirror


> Don,
>
>
>
> Your point about the deformations caused by edge supports on
thin glass is
> very interesting. It seems that PLOP does not consider this
effect
> whatsoever. You briefly refer to an alternative support
mechanism to address
> this issue. Can you elaborate a bit on the radial support
structure of your
> inclined tester.
>
>
>
> Thanks,
>
> Ted.
>
>   _____
>
> From: Don R Surles [mailto:Don.R.Surles-1@usa.dupont.com]
> Sent: Friday, May 09, 2008 2:17 PM
> To: tcohen@blakeglobal.com
> Cc: atm@atmlist.net; atm-bounces@atmlist.net
> Subject: Re: [ATM] Large Thin Mirror
>
>
>
>
> you will need support during grinding, polishing & figuring
that does not
> introduce forces into the mirror, ie, make the support flat and
strong.  i
> used 2 pcs of 1" thick plywood for a thin 24 inch mirror with
no problemos.
>
> testing the thin mirror is a bit more problematic...most test
setups support
> the mirror on the edge with blocks, dowels, or straps...all of
these will
> introduce forces into the thin mirror that will prevent getting
meaningful
> measurements.  can you say ying yang!
>
> an alternative testing arrangement that allows the thin mirror
to be
> supported on its back, ie, a tilted mirror cell with tester at
an incline,
> or put the mirror into the scope and star test, is the best way
around the
> perpendicular problem.
>
> Don...
>
>
>
>
>
>
> "Ted Cohen" <tcohen@blakeglobal.com>
> Sent by: atm-bounces@atmlist.net
>
> 05/09/2008 04:49 PM
>
>
> To
>
> <atm@atmlist.net>
>
>
> cc
>
>
>
>
> Subject
>
> Re: [ATM] Large Thin Mirror
>
>
>
>
>
>
>
>
>
>
>
> Dale,
>
> Rotation of the glass during grinding is not in question. The
question you
> are raising addresses whether one can grind, polish, and figure
on one type
> of surface (perhaps plywood, rubber, foam backing, carpeting,
or pitch) and
> then take the finished mirror, mount it in a floatation mirror
cell, with
> its different dynamic qualities, and expect the figure to be
the same in
> both cases. It would seem that when grinding and figuring you
would want the
> glass to have the same support characteristics as when the
glass is finally
> mounted. Am I wrong about this?
>
> Ted.
>
>
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