Re: [ATM] 40" mirror some ideas

[Jeff Anderson-Lee <jonah@eecs.berkeley.edu>]

If I recall from earlier e-mail with Jean-Guy, the posts were not placed 
by Plop.  However the placement in rings is very close to the 81 point 
cell design I independently came up with.   Were I to repeat it on my 
own I would probably use Plop to determine the post placements.

If it were in an 81-point cell a 36 by 1/2 inch flat mirror would have 
roughly 23nm RMS; presumably a slumped mirror of similar diameter would 
have similar RMS.  Not great, but better than 1/4 wave.  If it was 3/4 
inch thick instead, Plop would predict roughly 11nm flex in a 36 inch 
flat mirror.  At one inch thick, it becomes a quite respectable 6nm RMS.

However, the fused blank is not equivalent to an 81 point cell for a 1/2 
inch mirror.  The fused pegs are very different in behavior than a 
wiffle tree support point that only acts perpendicular to the mirror.  
Exactly how I cannot presume to predict.  Jean-Guy's ancedotal evidence 
suggests that its has considerably more stiffness than a simple 1/2 inch 
thick mirror.

Jeff Anderson-Lee

[Reasonable people adapt themselves to the world. Unreasonable people 
attempt to adapt the world to themselves. All progress, therefore, 
depends on unreasonable people. -- George Bernard Shaw]


Vladimir Galogaza wrote:

>The blank of Jean-Guy has two thin plates connected with 82 pegs.
>I do not know how are peg locations determined, and I wander
>what will PLOP say about that mirror (front plate only)
>resting  on a 82 point cell. Because it seems to me that this lightweight
>mirror ca be treated as front plate resting on its 82 "point" support cell
>though fused pegs are even further from points than controversial pads.
>What will be calculated surface rms.
>Mark, can you do it please?
>  
>


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