Re: Re[2]: [ATM] RE: Silicone Failure

["David Harbour" <scarab2@cox.net>]

Jerry,


"Thou shalt not look for shortcuts in making a telescope"

Seriously, friends, I read some sage advice somewhere, and have had it
validated in everything I have accomplished: seek the longest way to build
something, write something, mount something. There is an  unspoken rule in
craftsmanship: the longer you take to craft something, the finer the results
will be. I have had this validated over and over again in my life; I have
built quite a few things- mostly telescopes. The fact that people are having
trouble with silicone is prima facia evidence that they should be seeking
less risky solutions (more TIME CONSUMING) solutions. In my pursuit of
perfection, I actually looked for ways to make the project last longer. One
of the contributors to the Albert Ingalls/Scientific American 3 volume atm
books said: "the purpose of a hobby is to kill time".

The whole concept of the Dobsonian, for instance, is one Kolossal shortcut.
The largest mounting I ever built required 3,500 hours, 3.5 years to build.
It was very fine; no field rotation, one person transportable. No silicone
in it, never would have been. The mirror cell platform was designed to be a
platform for a variety of experimental rockers on axles, or astatic
levering, for mirrors between 12" and 18". The thought of that grey stuff,
with its propensities to flex, and sometimes lose its grip, would never have
been an option in my mind. My mirror cell platforms are designed to be well
ventilated (cutouts, like in aviation design) but strong, with radial struts
to locate rockers and their bearings. My old 12.5" would routinely carry
1,000X with no visible distortions. No fans, no silicone. See it here: I
used to have it in kit form; it was easy and cheap to build, and it was just
as one person transportable as any Dobbie. Took longer to build, that's all.
NO FIELD ROTATION:

http://www.atmsite.org/contrib/Harbour/StoppingDown.html


"Nothing tests truth like time"

On the other hand, "Different strokes for different folks". Good luck to all
of you silicone fans. The grey stuff does make the neatest lap molds you
ever saw: draw a picture of your lap, squeeze a bead of this stuff all over
it the pencil lines, (pick your own custom designed facets), wait till it
cures, soak the paper off, make your polishing tool with it- IT WILL NOT
STICK TO PITCH- and press, and polish away. So it does have an ideal use in
atm-ing.

David

P.S.- Do not use the kind that has acrylic pigment in it; it will stick to
pitch, and you will grind your teeth or break things, depending on what kind
of personality you have, when trying to separate the mold from lap. Grey RTV
only. "The grey stuff".


----- Original Message ----- 
From: "Jerry Reddell" <jerry.p.reddell63@sbcglobal.net>
To: "ATM" <atm@atmlist.net>
Sent: Friday, May 27, 2005 11:35 AM
Subject: RE: Re[2]: [ATM] RE: Silicone Failure


> Silicone mounting of mirrors has been highly successful by a number of
> people.  I personally believe all the "bad press" is that some people have
> made improper assumptions about its properties, applications, and use in
> analyses.  Those assumptions include things like considering it a rigid,
> none flexible material (as if it 'welds' the mirror to its cell attach
> point) which cause mirror distortions.
>
> Jerry Reddell
>
> -----Original Message-----
> From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net]On Behalf
> Of Richard
>
> Subject: Re[2]: [ATM] RE: Silicone Failure
>
>
> Hi David,
>
> Friday, May 27, 2005, 1:01:22 AM, you wrote:
>
> DH> Don't mount mirrors with it
>
> Why not?
>
> --
>
> Best regards,
>  Richard
>
>
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>


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