RE: [ATM] 40" mirror some ideas

["Scott Milligan" <starzkey@charter.net>]

Picking up on this latest idea, have you thought of contacting Peter
Wangsness, owner of Wangsness Optics in Tuscon?  His process can cast a
lighweighted, near net shape pyrex blank in situ.  I just recently acquired
a 32" F/3 part for a friend's project from him, and the total weight for
this blank (5" thick at the center, tapering to 1.25" thick at the edge) was
only 90 lbs.  The thickest single cross-section is about 0.75", which should
lead to very fast equilibration times under the sky.  The cost was
considerably less than I had first estimated (about 10k); more than the
simple 2" thick sheet, to be sure, but perhaps not out of the question for a
major ATM project.

Scott Milligan


-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Mel Bartels
Sent: Thursday, December 23, 2004 8:40 PM
To: atm@atmlist.net
Subject: Re: [ATM] 40" mirror some ideas

> I would say, study Palomar and look into the big mirror discussions
> from the 30's and the 40's.  Old technology that got the job done.

David is absolutely on the correct track here.  Get a 40 inch x 8 inch thick

primary, and have it sand blasted/cored/whatever to create a cellular 
pattern on the backside with a 1 inch thick face plate.  That way you'll 
have the flex of a 20 inch x 2 inch thick, yet the weight will (only) be, 
oh, 6x greater than that of the 20 inch.

In otherwords, get rid of the deadweight glass that is doing you no good, 
and causing an engineering trainwreck with a he-man mirror cell and the 
required humongous mounting.

Mel Bartels 

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