From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


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{at}nethere.com
NEW! http://bobmay.astronomy.net

--- BBBS/NT v4.00 MP