[ATM] Re: RTV, You Will Comply

[jonah at eecs.berkeley.edu (Jeff Anderson-Lee)]

Steve Houlihan wrote:

>Hi Jeff,
>
>Sorry I called you John in an earlier post.
>  
>
No sweat.

>Your last paragraph has me confused.
>
>"Thus, a 1/4 inch steel backplate should be stiff enough to support a 16
>inch mirror on 9 RTV blobs, with no wiffle tree. Then again, a 9 point
>cell is easy enough to make with just RTV, so why bother?"
>
>I'm beginning to believe that RTV and a flat plate can make a good cell, but
>what do you mean by "a 9 point cell is easy enough to make with just RTV".
>How is this different from the 1/4 inch steel plate with 9 RTV blobs?
>  
>
What I meant is, that you can make three triangles out of thinner stock 
(e.g. 1/8th inch steel plate) and RTV them to the mirror while mounting 
them on three collimation points and you are done.  You then have more 
open ventilation to the back of the mirror and less thermal mass.   
True, with a solid plate you could do forced ventilation, but that's 
another level of complexity.

>Then the next obvious question is......"How do you support the 1/4 inch
>steel plate?    It never ends!!!
>  
>
If you check the Plop.gr files appended to the prior post, you will see 
where the 1/4 inch steel plate gets mounted on three points.  If you run 
Plop, you can see that these points are placed such that the three 
mirror support points lie along a similar flex contour so that the 
plate's flex will mostly be the same at all nine mirror support points, 
reducing its effect on the mirror.

Of course the next trick is to figure out how to support the mirror and 
the plate so that the RTV can be applied and set with minimal strain on 
the glass.  That is left as an exercise for the student.

Jeff Anderson-Lee
Sacramento, CA