RE: ATM 16" "sling"?

["Paul LeFevre" <lefevre@midway.com>]

Albert Highe wrote:
> The RTV adheres very well to clean stainless steel. As with all adhesives,
> increasing the surface area always helps. I use stainless steel T-nuts to
> support and hold my 12.5" mirror. I roughened the surfaces with
> sandpaper to
> increase the surface area and insure that they were clean. As for aligning
> the mirror cell, I attached it to the upside-down mirror. I padded my
> surface well, and then laid out some large sheets of clean paper, and then
> laid the mirror silvered side down. I then positioned the mirror
> cell on the
> back and when I was finally convinced I had it centered, I marked the back
> of the mirror by tracing out the support points of the mirror cell on the
> back of the mirror. I then removed the cell, dispensed my RTV, and then
> gently lowered the mirror cell into position. You can either let the cell
> provide the contact force and dictate the thickness of the RTV, or you can
> control the thickness of the RTV blobs by placing washers at key points.
> Once the RTV cures, you can slide the washers out and invert the cell.
>
> You can see an image of how I did this on my website:
>
> http://pw2.netcom.com/~ahighe/12_5ultra.html

I had the pleasure of seeing Albert's scope at Mt. Lassen a couple of months
ago -- wonderful craftsmanship.
I wish I had know to ask about putting the mirror upside-down and attaching
the cell...Doh!  Why didn't I think of that?!?  In a similar way, however, I
used popsicle sticks as spacers...had the cell sitting face-up, put the RTV
on the stainless steel bolt heads that the mirror would sit on, then stacked
up popsicle sticks between the attachment points higher than the RTV.  I
then set the mirror down on the sticks, slid it around until it was aligned
perfectly, then removed a couple of sticks from each stack until the mirror
hit the RTV and "squished" it (technical term).  I was left with 2 popsicle
sticks in each stack, a little less than 1/4".  Once the RTV was cured I
removed the sticks.  The 12.5" full-thickness Pyrex mirror thus mounted does
very well optically, and has held in place quite nicely through 8 months of
long trips and bouncy roads.

Paul

Paul LeFevre
http://www.slip.net/~lefevre/scope.htm