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Sand Blasting large mirror blanks for web structur

Started by gordonlynnbrown, 05/12/2011 08:33AM
Posted 05/12/2011 08:33AM Opening Post
Hi All,
Acknowledging that webbed mirrors are lighter; cool more rapidly that full thickness mirrors; and offer more rigidity, facilitating fabrication, and avoiding astigmatism; has anyone investigated sandblasting older thick blanks to where they would have a webbed pattern?

It is anticipated that removal of the glass via the blasting process would generate strains. Would the blank have to be re annealed? Could it be re annealed?

Regards,
Gordon
Posted 05/13/2011 05:29AM #1
A hammer might work best. Break that old, thick blank into pieces and send the Pyrex off to be recast into a webbed blank. My former astro club had a 20" Newt with a traditional thickness solid mirror. It was in an observatory on a huge chain-driven fork mount. Thermal stabilization took 4-6 hours, and on some nights it never settled down.

Jim McSheehy
Posted 05/14/2011 04:10PM #2
Gordon Brown said:

Hi All,
Acknowledging that webbed mirrors are lighter; cool more rapidly that full thickness mirrors; and offer more rigidity, facilitating fabrication, and avoiding astigmatism; has anyone investigated sandblasting older thick blanks to where they would have a webbed pattern?

It is anticipated that removal of the glass via the blasting process would generate strains. Would the blank have to be re annealed? Could it be re annealed?

Regards,
Gordon

This has most assuredly been done over the years. I am reaching way back, but I believe Tom Johnson had this done on the 18-inch blank of his first big (pre Celestron) scope.

Uncle Rod

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Posted 05/14/2011 10:51PM | Edited 05/14/2011 10:52PM #3
Gordon,

Another option, although seems far-fetched is machining with diamond tools to get the web pattern.

I have seen this done on very expensive low expansion conical blanks.

Didn't say it was cheap, just possible. : )

David Simons