Re: ATM BVC Glass

[Steve Beccue <lsteve@daffodil.beccue.org>]

May I ask where the pyrex is obtained from?  What is the cost?
Are the pyrex and BVC both 2" thick?   

Thanks,
Steve



On Thu, 15 Aug 2002, Bill Prewitt wrote:

> 
> I did a 20" BVC 4 years ago and a 12.5 last winter.
> 
> The 20 blank had some wedge and an uneven back, but that was easily removed
> with a piece of window glass and 80 grit on a turntable. I understand he can
> blanchard them now.
> The recent 12.5 was flat and true.
> The blanks consist of a stack of disks, fused and slumped in a mold, so you
> can see a few flat bubbles way down in there once you polish out. They're
> apparently harmless and invisible once it's coated.
> 
> BVC is soft, so quick to grind and polish.
> Both blanks turned into good mirrors....
> It's very easy to figure because the image is bright, it stabilizes quickly
> on the stand, and it polishes quickly.
> 
> I suggest you nail down an acceptable wedge spec and get the curve slumped.
> 
> Having said all that, I chose 7740 Pyrex for the current 30" project.
> Larry Sayre and I had 30" disks waterjet-cut from opposite corners of a 40 x
> 60 slab for a good price locally. So I'll know more about pyrex vs bvc in a
> few months.
> 
> Bill Prewitt
> 
> Webpage of Telescope Making and Caving
> (My hobbies keep me in the dark)
> www.astrocaver.com
> 
> 
> 
> > Has anyone had any good/bad experiance with BVC glass in the 14"-20" size.
> > Any feedback is welcome.
> > Sam Orawski
> > Hamilton Canada
> >
> >
> >
> >
> 
>