[ATM] Re: RTV Considered Harmful

[frank at ucla.edu (Frank Henriquez)]

I've been following this discussion with interest. I've never made a 
mirror larger than a standard thickness 8", so bear with me as I ask 
some questions:

Why are all these mirrors being glued *TO* the RTV dots? Why not use 
the RTV dots as cushions and only apply the mirror once the dots are 
cured (ie, the mirror is loose, not glued). The give of the RTV should 
provide some flotation, and a similar edge support should keep it from 
flopping around in its cell. On the 24" in Astronomy (the only big 
mirror I'm familiar with) the flotation cell had teflon (or nylon - it 
looked & felt like teflon, though) pads on the triangles, and several 
brass screws (with teflon pads glued to their tips) provided just 
enough force to keep the mirror from flopping around. The mirror also 
had cork tipped clips to keep it in its cell - which some "helpful" 
graduate student thought had to be screwed down tight. This was the 
only time I'd seen any cell induced distortion on the mirror.

So again, why not let the mirror float/slide on the 
RTV/Teflon/nylon/cork pads in the cell?

Frank
--
Frank Henriquez Programmer/Analyst Jules Stein Eye Institute, UCLA
frank@ucla.edu  http://www.bol.ucla.edu/~frank/index.htm