[ATM] Second Thoughts on Mirror Support

[djd521 at comcast.net (Don D'Egidio)]

Stuart,

That's great running those tests on the RTV. The weight of my 17.5" mirror is 35 lbs. if you would need to use that in any calculations. I'm keeping an eye on this thread for all the eventual test reports. Doesn't JMI use RTV to secure the mirror in their NGT-18, which uses an 18 point flotation cell?

Don

----- Original Message ----- 
From: "Stuart Hutchins" <stuart452@earthlink.net>
To: "Mark Holm" <mdholm@telerama.com>; <atm@atmlist.net>
Sent: Thursday, February 05, 2004 0:11
Subject: Re: [ATM] Second Thoughts on Mirror Support


> 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
> >
> >
> >
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> >
> 
> 
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