[ATM] Re: ATM Digest, Vol 2, Issue 12

[artbianconi at blast.net (artbianconi@blast.net)]

2. Re: Re: Second Thoughts on Mirror Support (Stuart Hutchins)
5. Re: Re: Second Thoughts on Mirror Support (Jeff Anderson-Lee)
6. Re: Re: Second Thoughts on Mirror Support (Jeff Anderson-Lee)
8. RE: Re: Second Thoughts on Mirror Support (Peter)
10. Re: Re: Second Thoughts on Mirror Support (Jim Burrows)
13. Re: Second Thoughts on Mirror Support (Mark Holm)
14. Re: Re: Second Thoughts on Mirror Support (Mark Holm)

Many of the complex cells I've seen, are built on some really optimistic 
assumptions. Everyone assumes, for the example, that the moments and  
coefficients of friction at each support are precisely identical to others in that 
complex, multi-point system. That most are made of metal parts that shrink 
and expand with temperature adds yet another non-linear variable. Has 
anyone considered the effects of time and exposure on all those balance 
beams on their ability to maintain equilibrium?

The degree of torsional stiffness possible today, by the proper application of 
advanced composites, exceeds the dreams of even the most imaginative of 
engineers 25 years ago. That stiffness has made possible aerodynamic designs 
that would have been suicidal 15 years ago (forward swept wings for 
example).

I'll build my cell out of it. I am going to keep things simple.The 15"OD,  
1.625" thick mirror is Blanchard ground. It will sit on a multi-core, multi-
layer disk of bi-directional carbon fiber where each ply displaced 15 degrees 
from it's. neighbor. As complex as the load paths might be, this system should 
handle it with no deflection.  

The geometry of the cell is too complex to describe with words alone. Suffice 
it to say that it will resemble a thick wheel with one row of spokes, each 
having an "I" beam cross section.

A thin (0.020" film of Teflon will sit between the mirror and the cell. This 
relatively friction free interface should allow the mirror to seek it's own 
equilibrium.

The perimeter of the mirror is attached to an outer ring on the cell whose OD 
is about 2 inches larger than the mirror (17"). That's done with an advanced 
space age polymer developed for NASA (by Dow Chemical?) Perhaps six or 
eight webs of that material , around the perimeter of the mirror will alow the 
glass to expand, contract, and achieve some degree of geometric equilibrium. 
Different durometers are available.

No moving parts, a minimum of constraints and an optically flat,slippery 
surface. 

Will it work? I think so. If it doesn't  . . . . . I'll try something else.

Art Bianconi 

If this is the 15th "second thought" is it still a second thought?