[ATM] If it's in a supremely stiff cell, that does not twist,why would a thin mirror sag?

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

No Don, 

14.7 psi  and 176.7 sq in gives you a 15" mirror. It's good you responded 
however as I've gotten so used to working with film I failed to consider the 
less used option of an actual bag, which would not distort the mirror.

Typically I simply tape the film to the bench.

Thanks

Art

Art Bianconi wrote:
===================
Vacuum bagging will subject the mirror to about 2,500 pounds of
atmospheric pressure. I've some concern that lack of support caused by
the preground sagitta will allow excessive stresses to build. While it
would not likely crack the mirror, it could cause it to flex and
distort the surface. =================== Let's see: 2500 pounds,
~15psi, 167 sq in, R=sqrt(A/pi)=7 1/4, maybe 8" mirror. Actually
vacuum bagging subjects the mirror to very little additional stress. 
Because the mirror is in the atmosphere at all times, it is already
being subjected to ~15 psi.  As long as the bagging technique has
little or no rigidity on both sides of the mirror, you are OK.

Don