Re: ATM - Incredible offer

[Mark Suchting <masuch@cia.com.au>]

No I'm talking specifically about the two low `clear' patches visible in 
the photo, which are untouched by the generator, not the generator marks. 
Drawn Pyrex sheet typically can have  uneven surface areas which are left ( 
on the back ) by the glass vendor if the blanks are already generated down 
to minimum thickness.

~Mark


At 01:45 AM 10/29/2003 -0400, James P Crombie wrote:

>The marks on the glass in photo two are left by surface grinding on a 
>Blanchard grinder.  Commonly used to grind the two surfaces parallel.
>For something this large it was problably done on something like this
>http://www.blackclawson-cm.com/grinder.html
>Big sucker :-)
>
>-------------------------------------------------------------------------
>Date: Wed, 29 Oct 2003 12:02:31 +1100
>From: Mark Suchting <masuch@cia.com.au>
>Subject: Re: ATM Incredible Offer.
>
>Joe
>
>As far as I know, Corning only sells #7740 Pyrex in that size in 2 1/4"
>thick sheets. They do not _mold_ telescope blanks. Post -processors like
>Newport, United lens etc do the cutting, generating and annealing.
>
>The ripply low spots remaining in the photo:
>
>http://www.mwt.net/~nss/mirrors-2.jpg   look typical of the artifacts of
>drawn sheet Pyrex to me.
>--
>--------------------------------------------------------------------------
>
>James P Crombie
>
>Summerside                   Machinist
>Prince Edward Island         Amateur Astronomer
>Canada                       3D Designer
>
>E-mail                       jpcrombie@pei.eastlink.ca
>Astronomy webpage            http://www.jamescrombie.com
>Rhinoceros 3D webpage        http://www.jamescrombie.com/rhino/
>Mirror Grinder page          http://www.jamescrombie.com/pics/
>-------------------------------------------------------------------------- 
>
>
>