Back to Home

ATM Forum Message

Forums: Atm · Astrophotography · Blackholes · Blackholes2 · CCD · Celestron · Domes · Education
Eyepieces · Meade · Misc. · God and Science · SETI · Software · UFO · XEphem
RSS Button

Home | Discussion Forums | Amateur Telescope Making | Post
Login

Be the first pioneers to continue the Astronomy Discussions at our new Astronomy meeting place...
The Space and Astronomy Agora
OOPTH

Forum List | Follow Ups | Post Message | Back to Thread Topics | In Response To
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.

Follow Ups:

Login to Post
Additional Information
Google
 
Web www.astronomy.net
DayNightLine
About Astronomy Net | Advertise on Astronomy Net | Contact & Comments | Privacy Policy
Unless otherwise specified, web site content Copyright 1994-2020 John Huggins All Rights Reserved
Forum posts are Copyright their authors as specified in the heading above the post.
"dbHTML," "AstroGuide," "ASTRONOMY.NET" & "VA.NET"
are trademarks of John Huggins