Re: ATM 3/4" Plate glass .. the Max..

["Bob May" <bobmay@nethere.com>]

While slumping is probably going to be best for anything that large, you
don't have to at the 16" stage.  Larger mirrors, I'd do slumping just to get
the majority of the glass removal out of the way.
As to supporting a mirror like that, cast a loose plaster base, index the
glass to the support and apply a rubber or foam isolator for the glass.
Next comes careful work (no sitting there and just working one way for a
half hour) followed by the possibility that the glass will be ground with a
bit of astigmatism into it if the support is poor.  I'll note that a few
minutes with the 9 micron, or so, will generally get rid of the astigmatism.
You will also have to take care supporting the glass in the tester as it
will flex enough to start making changes to the apperance of the surface in
the testers.
I'll also note that the ultralight primary isn't going to be that great for
the Dob style scope as you will be adding weight to the rocker box so that
the bearings won't be so high up.  The ultralight mirror is a lot better for
something like a Cassegrain of some kind.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net