Re: ATM Mirror cell thoughts

[Aplanatic@aol.com]

Raphaël Guinamard wrote:

> I don't know of you transform arcminute to mm deformation, but it seems that
>  the above deviations are very good
>  So according to Dave calculation, and if I didn't make mistakes with the
>  stange units US people are using, 25 mm pads are enough for very little
>  deformation, but what about gluing "force" ?.

Ah, these damned "English" units will plague us to the end of our days, I'm 
afraid.  I used these strange and awkward units because I know the Young's 
modulus of RTV from experiments that I conducted using "English" rulers, 
micrometers and weights.  Sorry.  I should have converted it to a decent unit 
like kilo Pascals.

Anyway, I think that you could use even less RTV blob area for your mirror.  
You will be fine with 6 pads each 25 mm in diameter having a thickness of 3 
mm.  Should be overkill (a funny word that means you have way more than 
enough guns, ammo, and nuclear weapons to destroy your enemy, which in this 
case is mirror tilt).
  
>  I would fill more confident with 30 or 35 mm diameter pads for that point 
of
>  view .

I assure you that 6 25-mm blobs will be fine.  I have a 250 mm diameter 
mirror, 50 mm thick RTV'ed to a wooded base with 6 15-mm diameter blobs.  It 
takes 15 minutes to saw off the mirror for recoating.  RTV is very good at 
this application.  Just make sure that the mirror and backplate are clean and 
free of contamination before gluing.  If you are still worried, use mirror 
clips as a safety device.  Mirror "clips" should not touch the mirror, of 
course.

Dave Rowe.