You mean the RTV like the stuff for automotive gaskets? They make blue and
black...how big of a blot? I did get 100% silicone or might this be a bad
idea? You offered the use of cork...don't have any, is this critical?
At 10:27 AM 3/2/2005, you wrote:
>RTV is a good choice if your surface is well-prepared. We've used it.
>
>Don't do a bead (warping because of different thermal expansion rates) -
>do point contacts. For theory, google "mirror cell plop" to calculate the
>mechanical strain of a mirror against a plate. Looks like for a .875in
>thickness blank the max diameter is 8.7in. So a 4.5 is about .5in thick.
>Try for 3 equidistant points - it would help to have one in the center,
>but when you try to remove it you're going to have a difficult time, so
>it's your call.
>
>Clips are a bad idea anyway - use the cork you have if you can. But get
>off that old cement completely - they're incompatible glues. The cork
>probably rotted because it was layered between two nonporous surfaces, and
>cork is very hydrophiliac. My father-in-law would probably have put it in
>a low vacuum chamber for a few weeks, and done different pull tests to
>make sure that any one of the pad areas was big enough and strong enough
>to hold the mirror, but he worked on satellites at Ford Aerospace / Loral
>(see http://jolitz.telemuse.net/wljolitz.) :-)
>
>An excellent solvent for RTV is eucalyptus oil, but don't get too much of
>it on your hands (poisonous in quantity) nor let it near children / pets
>(keep it locked up). You can get some cheaply at the "Herb Room" in Santa
>Cruz.
>
>If you don't clean well enough, RTV doesn't adhere well and the weight of
>the mirror will cause sagging or (worse yet) fall off. RTV doesn't adhere
>well to enamels, BTW, so go to the metal surface. -l
>
>----
>We use SpamQuiz.
>If your ISP didn't make the grade try http://lynne.telemuse.net
>
>
> > -----Original Message-----
> > From: sf-bay-tac-bounces@No-Spam [mailto:sf-bay-tac-bounces@No-Spam]On
> > Behalf Of Mike J. Shade
> > Sent: Wednesday, March 02, 2005 8:41 AM
> > To: sf-bay-tac@No-Spam
> > Subject: [TAC] (OT) RTV and secondary mirror
> >
> >
> > I'm going to reattach the 4.5" secondary mirror for the 12.5"
> > Ritchey-Chretian. It looks like there were three cork pads,
> > about 1.5" and
> > these were glued to the back plate and the mirror was glued to
> > these...I'm
> > thinking that three buttons or RTV might be a better choice,
> > about the same
> > spacing but perhaps not quite as large...anyone have any thoughts on
> > this? Might it be better to put a thin bead at the edge? More
> > cork (which
> > I suspect might have been stressing the mirror a bit)?
> >
> > Clips are out of the question...
> >
> > Thanks...BTW. the original cork pads are destroyed and it looked like the
> > previous owner used windshield repair cement (that yellow looking stuff
> > that dries hard)...it doesn't look like RTV...
> >
> >
> > Mike J. Shade: mshade@No-Spam
> > Director, Sonoita Hills Observatory, Sonoita Arizona
> > www.sonoitaobservatories.org
> >
> > See work done at the observatory: http://c3po.cochise.edu/astro
> > under the "images & photos" panel on the left of the page
> >
> > Fight wasteful and obtrusive outdoor nighttime lighting:
> > International Dark Sky Association: www.darksky.org
> >
> > "I like the dark, it's cheap." Ebinezer Scrooge
> >
> >
> >
Mike J. Shade: mshade@No-Spam
Director, Sonoita Hills Observatory, Sonoita Arizona
www.sonoitaobservatories.org
See work done at the observatory: http://c3po.cochise.edu/astro
under the "images & photos" panel on the left of the page
Fight wasteful and obtrusive outdoor nighttime lighting:
International Dark Sky Association: www.darksky.org
"I like the dark, it's cheap." Ebinezer Scrooge
Received on Wed Mar 2 11:26:02 2005