Re: ATM 16" "sling"?

["Jan van Gastel" <jhm.van.gastel@mdw.vu.nl>]

I allready have a mirror cell for my 20", 2 inch thickness mirror. (Don't
have the mirror yet. Ordered it at Swayze Optical). It's an 18 points cell.
According to PLOP the deformation is less then 1/500 lambda. Actually, it
was a bit less, but when the cell was ready, I noticed that I had done a
liottle miscalculation, resulting in inequality of some angles between
support points. When I entered the figures of the actual angles and
distances, the accuracy was even better then with the original (equal angle)
figures.

I choose an 18 instaed of a 12 points cell (which was also a good
possibility) to have some room for errors. When I place the mirror a couple
of millimeters wrong, there will be no problem at all.

I have not decided yet whether I will use a sling or RTV. I know RTV,
because I made some very big aquariums with it. It is very strong and stays
elastic. But I only glued glass to glass untill now and I do not know how
good it holds to stainless steel.
Furthermore, I don't exactly know how I am ging to plce the mirror on the
silliconde blobs. I see myself there, standing with 48 lbs mirror above the
sillicone. I can't look under it, so I can't see the exact locations. If I
place it wrong I will have to move it in plce, making smearing the RTV out
over the triangles. Well, maybe this is some kind of a nightmare, but I
didn't make the time yet to think of a good solution.

I also followed the thread about the width of teflon pads, which has been
very informative.

Jan
http://www.geocities.com/janvangastel/

----- Original Message -----
From: Krajci Tom J Maj 27 OSS/IN <Tom.Krajci@cannon.af.mil>
To: <atm@shore.net>
Sent: Sunday, August 13, 2000 7:24 PM
Subject: RE: ATM 16" "sling"?


> *IF* you feel you need a sling (or similar edge support scheme)...make it
of
> a material that does not change length with changes in humidity...steel
> banding, bicycle chain, etc. will work fine.
>
> However, I (and many others) don't feel a sling is needed.  Design and
build
> a good support system (how thick will your mirror be?  My sixteen inch
> mirror is 1.5 inches thick and is on a six point support), and then RTV
> silicone glue your mirror to the cell support pads.  No sling, no
retaining
> clips needed, collimation is held very well at all elevations.
>
> I recommend you download PLOP and tinker with various support schemes for
> mirror cell designs...we'll help you if PLOP seems to be a large mouthful.
>
> Good luck!
> Tom Krajci
>
>