[ATM] Second Thoughts on Mirror Support

[stuart452 at earthlink.net (Stuart Hutchins)]

Mark,

This remarkable thread has developed 3 ends! And it is triggering some
interesting new mirror cell analysis.

The original poster, Steve Houlihan, has the mirror cell with the ball-joint
pivots behind the whiffle triangles, not a solid plate.  Therefore his
forces (minus ball-joint sticktion) will be transmitted right through the
three compliant RTV pads to produce uneven support forces at the mirror.
These forces can be easily estimated as I outlined in my first post.  Then
PLOP can show how serious the deformation is.

This is a different problem than the solid plate analysis by Jeff
Anderson-Lee.  Jeff is the kind of PLOP driver I want to be when I grow up.
His work may show why Don D'Egidio's 17.5 Discovery seems to work OK when
many of us don't think it should.   Outlining an acceptable design envelope
for the solid-plate+RTV cell would be a significant contribution to the ATM
art.  I just made a test sample of RTV between two 1" square aluminum plates
to measure modulus.  Will post measured value for a "typical pad" in about 5
days after the stuff cures.

BTW, Mark, I hope I didn't seriously breach good netiquette by listing your
website in my post without asking.
I got it, of course, off this list and found it very instructive. Thanks.

Regards,

Stuart Hutchins

----- Original Message -----
From: "Mark Holm" <mdholm@telerama.com>
To: <atm@atmlist.net>
Sent: Wednesday, February 04, 2004 7:42 PM
Subject: Re: [ATM] Second Thoughts on Mirror Support


> Looks like your mirror is plenty thick.  This isn't quantitative, but
> the modulus of silicone RTV is a whole lot lower than the modulus of the
> glass mirror.  Most of the deformation you sketch is going to end up
> compressing and stretching the RTV instead of bending the glass.  Some
> of course will get through to the glass.  Will it be small enough to
> ignore?  I don't know.
>
> Mark Holm
> mdholm@telerama.com
>
>
>
>
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