Plate glass questions.

Ralph Seguin (seguin@vr2.engin.umich.edu)
Fri, 14 Jul 1995 17:50:06 -0400

Ok. I've heard that plate glass is evil. Impurities, bubbles, bad thermal coeff and other properties, ... However, I've come upon some of it. I have some .5" and will be getting some .75" and possibly 1" thick.

What I want to know:

1. How do you cut circular blanks out of it? 2. Grinding it? Anything different? 3. What is the minimum thickness to diameter ratio to prevent sagging? Ie, with my .5" thick glass, can I expect intolerable results from an 8", 9", 10", ... blank? I know with glass this thin, that I'll have to go with a really slow f/ratio. 4. Got any clever cell designs to prevent sagging? 5. Am I crazy to even think of attempting this? 6. Got a means to melt it all down and spin cast it into a 1 meter class blank with pregenerated curve? ;>

http://www-name.engin.umich.edu:8001/people/seguin/astronomy/MirrorLab/Mirro rLab.html

What worries me is the thickness and how I'm going to get it cut into circles.

Oh, I forgot to mention, that I want to do this inexpensively; I cannot afford most pyrex blanks, otherwise I would simply go that route.

Thanks, Ralph