[ATM] Re: Second Thoughts on Mirror Support

[stuart452 at earthlink.net (Stuart Hutchins)]

Hi Steve,


----- Original Message -----
From: "Steve Houlihan" <sho@surfnetUSA.com>
To: <atm@atmlist.net>
Sent: Friday, February 06, 2004 6:55 PM
Subject: [ATM] Re: Second Thoughts on Mirror Support


> I started this thread last week and am fascinated at how it has
progressed.

You did it! You started the hottest thread in recent memory just by asking a
simple question on what you thought was a good, proven cell design.

> I have used the actual sizes of my cell and mirror and done a few simple
> calcs.  The worst case for uneven forces being applied to the back of the
> mirror would be when one of the triangles was oriented horizontally and
the
> mirror was vertical.  The moment arm from the ball joint to the center of
> the mirror is 1.75 inches and the mirror weighs about 12 pounds.

==> measure perpendicular from the back of mirror to the center of the ball,
not to mirror center. ==
==> looks like less than one inch to me, but I can't measure the photograph
==

 1/3 of the
> weight is carried by each triangle so the moment applied to the mirror
would
> be 12/3 or 4 pounds times 1.75 inches which is 7 in-lbs.  This is resisted
> by the two RTV pads that in the worst case are only 2 inches apart.  This
> puts a 3.5 pound force into the mirror and another 3.5 pound force just 2
> inches away in the opposite direction.  That seems like a lot of bending
to
> me.

I, for one have not forgotten that you've not yet received an answer to your
specific problem.  It is an interesting one to me, and practical, because
many are tempted to make the cell and glue down the glass in a similar
fashion.  If you recall, I guessed the pad forces in the 1 to 3 lb range.  I
also boldly said that Plop could analyze the distortion, but I've gotten
feedback from experienced users that Plop won't take these wierd
assymetrical forces.  However, an approximation of the size of the "S" can
be gotten from basic one dimensional beam bending theory and a spreadsheet
or simple Basic program.  I plan to do that this weekend, so thanks for
posting your dimensions and force estimates.

Regards,  Stuart