From: "Scott Berfield" 
To: 
Reply-To: "Scott Berfield" 


 For my 8" I used RTV pads. I made a small divot in the substrate, stuck
a small (2mm) bead in the divot with a dab of glue, then applied enough RTV
to squish out to around 3/4" in diameter. Three beads and three blobs,
then sat the mirror on it and avoided moving it at all until a full day had
passed. For that scope I also had side supports made from small metal
angles with holes drilled in them. There was 1/8" between these and
the mirror. I squeezed RTV through the holes to make side support pads. The
beads act as point supports and the RTV allows flex and holds everything in
place. The side pads are just because I am paranoid.

-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net] On Behalf Of Jeff
Anderson-Lee
Sent: Thursday, May 29, 2003 5:12 PM To: Jeremiah J. Burton; atm{at}shore.net
Subject: Re: ATM Silicone mirror attachement


Jeremiah J. Burton"  asked: "I have
an 8" mirror that I'm going to build a new cell for.  How thick of
spacers should I use when attaching the mirror to the cell with
silicone?"

I recall reading somewhere that pad sizes of about 1/8in (3mm) thick by 1in
(25mm) diameter worked well.

Ah, here it is:
On Nov 7, 2001, Michael Lindner wrote (Re: ATM mounting primary mirror):

"...I queried several people who had had good and bad experiences with
silicone (thanks, guys), and then ran some tests varying the size and
thickness of the silicone. What seems to cause problems with
collimation/astigmatism are pads that are too thin or too thick, or (to a
lesser extent) pads that are too small or too large. I settled on pads
1/8"
thick and 1" square. The scope holds collimation well, with no
detectable movement of a laser collimator spot from horizon to zenith
(which is better than what I experienced with the sling)."


Jeff Anderson-Lee
Sacramento, CA

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