Good question, Phil. My father-in-law, the satellite space engineer, didn't like silicone grease for exactly this reason - how do you clean it off?
In the lab he would have taken it down to the metal, and then taken it down further because he would have been worried about the wetting as he was cutting it. Degreasing was an incredible preoccupation because any film would lift off slightly, and that meant bad things for satellites, because of all that Corona discharge, mechanical fatigue from the rocket ride creating pendulums that get in harmonic oscillation, ... :-)
But since we're on earth and we can't definitively prove it's completely cleaned (because we don't have all that stuff from Loral), but we're not going on a rocket into space, I'm going to get simple. We let it sit until it isn't smelly.
Euc oil is very volatile (it stinks!), and a very small amount works really well in loosening that RTV *if* you have to remove it. So let it sit until and only until it absolutely doesn't stink - remember, your nose can pick up even the smallest amounts of a volatile oil, unless you suffer from anosmia, in which case get a middle-aged woman to sniff, because it turns out in studies she has on average the best sense of smell. (One interesting item I came across in a very interesting discussion on smell is even though men often claim they can't smell anything, their sperm may smell their way to the egg, and women can sniff the "scent of fear" - see http://www.cf.ac.uk/biosi/staff/jacob/teaching/sensory/olfact1.html).
A tiny little bottle should last, well, forever (unless you put in your bubble bath), so you might want to offer it to the ATM class for their use if you don't need it anymore. -l
----
We use SpamQuiz.
If your ISP didn't make the grade try http://lynne.telemuse.net
> -----Original Message-----P T Chambers
> Sent: Wednesday, March 02, 2005 2:40 PM
> Hey Lynne
>
> Ok, euc oil is great, but, how do you clean off the oil???
>
> Alky???
>
> Just wondering.
>
> ---------
> Phil Chambers [ptchamb@svpal.org] (S.F. Bay Area - Calif. USA)
>
> On Wed, 2 Mar 2005, Lynne Jolitz wrote:
>
> > Oh, gee, like it really fills up the room and suffocates everyone and
> > destroys lungs and stuff, so you have to use the more expensive
> product. :-)
> > It's just sticky stuff. Anyone who tells you otherwise is selling
> > something. -l
> >
> > ----
> > We use SpamQuiz.
> > If your ISP didn't make the grade try http://lynne.telemuse.net
> >
> > -----Original Message-----
> > From: sf-bay-tac-bounces@seds.org
> [mailto:sf-bay-tac-bounces@seds.org]On
> > Behalf Of Grimly Fiendish
> > Sent: Wednesday, March 02, 2005 11:25 AM
> > To: The Astronomy Connection
> > Subject: RE: [TAC] (OT) RTV and secondary mirror
> >
> >
> > Lynne,
> > Actually it is silicone, the MSDS lists it as RTV Silicone Adhesive
> > Sealant , and personally I would be reluctant to use it because it out
> > gasses. I would recommend the GE Silicone II that Michelle uses
> because the
> > only out gassing is a little bit of acidic acid which is not as
> corrosive as
> > the RTV materials.
> >
> > Kevin
> >
> > Lynne Jolitz <lynne@telemuse.net> wrote:
> > Room tempature vulcanizing rubber (RTV) is also called "silicone"
> > rubber. You can buy it in hardware stores, but you've got to read the
> > ingedients labels carefully (easy to get fooled). You want to
> use one that
> > is an adhesive - RTV is used in many other apps, such as caulking, but
> > that's not what you want. Suggest clear (less filler).
> >
> > the blot should be enough such that one can hold the mirror
> comfortably.
> > Usually a dab is good enough to hold quite a bit because too
> much induces
> > astigmatism with a thin mirror. More isn't necessarily better.
> Thinner films
> > of RTV work better than thicker films.
> >
> > Clean off all of that old stuff (cork, glue, paint, moths)
> - get rid of
> > it all right down to the metal and glass, keep the RTV as thin as
> > possible, - and start fresh. The blobs should be squeezed down to about
> > 1/16th of an inch thick and no bigger than one inch in diameter
> w hen you
> > adhere the metal to the mirror, so you have about 3 square inches of
> > adhesive holding your 4.5in mirror.
> >
> > It's a bit of an art. But if you find you do too much, you
> can remove it
> > carefully with the eucalyptus oil and an exacto blade and try again. -l
> >
> > ----
> > We use SpamQuiz.
> > If your ISP didn't make the grade try http://lynne.telemuse.net
> >
> >
> > > -----Original Message-----
> > > From: sf-bay-tac-bounces@seds.org
> > [mailto:sf-bay-tac-bounces@seds.org]On
> > > Behalf Of Mike J. Shade
> > > Sent: Wednesday, March 02, 2005 10:25 AM
> > > To: The Astronomy Connection
> > > Subject: RE: [TAC] (OT) RTV and secondary mirror
> > >
> > >
> > > 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 hav e
> > > 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@seds.org
> > > [mailto:sf-bay-tac-bounces@seds.org]On
> > > > > Behalf Of Mike J. Shade
> > > > > Sent: Wednesday, March 02, 2005 8:41 AM
> > > > > To: sf-bay-tac@seds.org
> > > > > 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
> > > > &g t; 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@theriver.com
> > > > > 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@theriver.com
> > > 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 Thu Mar 3 10:03:04 2005