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Posted by Robert May on August 14, 2002 19:15:14 UTC

Where you say thermal expansion in #3, you really should be saying differential thermal expansion. The glass, once it comes to thermal equilibrium, will be of the same shape, albeit a few tenths of a thousandths of an inch bigger in diameter, as at the other temp. It's while the temp is different across the thickness and/or the diameter, you get stresses that deform the glass.
The next thing is that you can indeed use a high expansion material for the base of the glass because the glass is merely sitting on top of the points, not attached to them, and thus, the support can move about and not affect the shape of the glass. If you attach the glass to the support, you can get distortions that way.
Another item is that as you go towards the horizontal, you run into the problem of potato chipping of the glass as it's no longer sitting on the back supports but rather sitting on the edge supports with the top folding over.

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