[ATM] SEC: UNCLASSIFIED:-Primary Mirror Retainers

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

James Lerch wrote:

>----- Original Message ----- 
>From: "Bob May" <bobmay@nethere.com>
>  
>
>>Put any stress on the bolt in the center and you are flexing the mirror and
>>it will show a trefoil shape to the stars as a result.
>>Without the stress, stars at the horizon (with a thin mirror) will tend to
>>get a wierd shape as the center will tend to tilt a bit causing a trail in
>>the shape of the star although that shape won't be too strong.
>>    
>>
>Hi Bob,
>
>The obvious answer is to drill a hole in the center of the mirror.  (I smile
>while I say that, but there is a bit of honesty in the statement..)
>
>If the hole is made large enough to accept a rather large sturdy rod with some
>type of linear bearing (like Teflon or bronze sleeve), we can support the mirror
>so it won't slide off the cell, but leave 4 degrees of freedom (tip, tilt,
>piston, and rotation).  Ron is seriously considering this option on his 22" 3/4"
>edge thick plate glass primary.  Ron's currently using (and cursing) a sling
>support..
>
If you just glue/RTV the support to the back you may have some flex as 
Bob suggests, since the mirror's weight is not through the point of 
contact when the mirro is off-vertical.

Drilling a hole in the mirror (in the secondary's shadow) and passing a 
bolt through would help that issue, but now you have the almost the 
whole mirror's weight supported by a single bolt though a single hole 
when near the horizon.  Why would this be better than a good edge 
support of some sort?

Jeff Anderson-Lee