FW: ATM Mounting Large, Thin Mirrors

["McHatten, Shawn" <Shawn.McHatten@aliant.ca>]

> -----Original Message-----
> From:	McHatten, Shawn 
> Sent:	April 4, 2001 4:12 PM
> To:	'Aplanatic@aol.com'
> Subject:	RE: ATM Mounting Large, Thin Mirrors
> 
> 
> snip>
> The significant problem with the standard floatation cell and sling is the
> transverse (compressional) forces applied to the mirror when the telescope
> is pointed toward the horizon.
> 
> 
> Why not glue permanent magnets on the back of the mirror at the points
> that the mirror cell would normally sit and make sure that the points on
> the cell were ferrous (magnetic) metal. If my calcs are right an 18in
> mirror 1in thick weighs a little over 20 pounds. With an 18 point cell
> each magnet would have to hold a little over 1lb of weight when the mirror
> is tipped to the horizontal. So say it's 2lbs. I would assume the force
> directed on the magnets to slide sideways because of the expansion of the
> glass would be considerably more than 2 lbs. So get magnets with 2lb
> holding force and let them slide on the cell with expansion force but hold
> solid with the force of gravity. We might have to glue a center point to
> the center of cell/mirror to encourage the mirror to expand radially even
> around the center instead of downward if the mirror was tipped while the
> mirror was expanding but I'm not sure if this would be a problem. I just
> thought that this idea would be a compromise between RTV which does not
> let the mirror slip while tipped but also no expansion capabilities,
> versus just using a sling and normal gravity held cell which may allow for
> expansion but suffers from distortion from the sling. I looked through the
> last couple of years archives and didn't see any mention of this idea so
> hopefully this will not elicit a "here we go again" :-). Hopefully I've
> explained it well enough. Let me know how crazy this thought is.
> 
> Shawn 
>   
>