Re: Re[6]: ATM 1" thick glass at $450 for 13" plate!?

[Richard Schwartz <richas@chelsea.ios.com>]

-- [ From: Richard Schwartz * EMC.Ver #2.5.02 ] --

I got back to my supplier, and by eliminating the polishing of the edge, he
dropped the price for 3/4 by 13" portholes from $34 to $18.  He still
refuses to work with 1" glass because he says there is a lot of waste.

If you go by the Toshimi Taki articles in S & T, 3/4" glass that size is
very close to the limit for a 9 point support.  It would be fine for an 18
point support if  you want to buy into the extra complication.  If your
figure is perfect, and your secondary is perfect, and your collimation is
perfect, a 9 point would be OK with 3/4 inch glass.

I will be sounding some more glass suppliers.

Who ever heard of polishing the edge of a porthole, anyway?  They said most
of that stuff is used for table tops.

BTW, the Toshimi Taki articles give the deflection for 5, 7.5, 10, and 12.5
percent thickness.  I have calculated a nice smooth curve fit that closely
matches these four values, but I left it in my other house.  I will retrieve
it and publish it tomorrow if anybody is interested.  This will allow
calculation of the deflection in a mirror of any practical thickness and
aperture.