Re: [ATM] Gluing mirrors - was Coulter secondary adhesive

[Mike Lockwood <melockwo@uiuc.edu>]

Chris,

Chris Dalla Piazza wrote:
> I plan on gluing both my primary and secondary mirrors.  The secondary will
> be attached to a Protostar support and the 6.5" primary to a 6061 aluminum
> mount.
> I was planning on using small shirt buttons as spacers and using spots of
> silicon.  The reason for gluing the primary is to avoid mirror shift in this
> fast f/4.5 system for more stable collimation.
> For the primary, I was wondering what the suggestions would be for the size
> and number of the silicon spots or if there is a better approach.  My
> thinking is that the silicon will be flexible enough to absorb the stress
> from the thermal expansion of the aluminum yet using 9 or more small spots
> will create a stiff enough bond to keep the mirror in place.

Do you need a 9-point support?  Will 3 points be sufficient?

Be careful when gluing to aluminum.  Our 5.5" elliptical secondary on 
our 30" scope goes astigmatic when the aluminum is heated or cooled.

I would be tempted to start with a 3-point support and no glue, and 
then add very small globs of glue (just enough to control the position 
of the mirror) to one support point at a time while evaluating the 
results optically and in terms of mirror shift.  The glue could be 
added right beside a Teflon support pad.  The pad could later be 
removed, if desired, or it might be OK to leave it in place.

	Mike Lockwood

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