Re: ATM 16" "sling"?

["Albert Highe" <ahighe@ix.netcom.com>]

Jan,

The RTV adheres very well to clean stainless steel. As with all adhesives,
increasing the surface area always helps. I use stainless steel T-nuts to
support and hold my 12.5" mirror. I roughened the surfaces with sandpaper to
increase the surface area and insure that they were clean. As for aligning
the mirror cell, I attached it to the upside-down mirror. I padded my
surface well, and then laid out some large sheets of clean paper, and then
laid the mirror silvered side down. I then positioned the mirror cell on the
back and when I was finally convinced I had it centered, I marked the back
of the mirror by tracing out the support points of the mirror cell on the
back of the mirror. I then removed the cell, dispensed my RTV, and then
gently lowered the mirror cell into position. You can either let the cell
provide the contact force and dictate the thickness of the RTV, or you can
control the thickness of the RTV blobs by placing washers at key points.
Once the RTV cures, you can slide the washers out and invert the cell.

You can see an image of how I did this on my website:

http://pw2.netcom.com/~ahighe/12_5ultra.html

Albert

----- Original Message -----
From: Jan van Gastel <jhm.van.gastel@mdw.vu.nl>
To: Krajci Tom J Maj 27 OSS/IN <Tom.Krajci@cannon.af.mil>; <atm@shore.net>
Sent: Sunday, August 13, 2000 11:53 AM
Subject: Re: ATM 16" "sling"?


>
> 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
> >
> >
>
>