Re: ATM 3/4" plate glass.. how big???

[Larry Sayre <lsayre@apk.net>]

Russell Jocoy wrote:

>
> ("atm@shore.net")
>
>    O.K. you edler mirror makers how far can you go with a 3/4" plate 
> glass blank???
>    Is 16" too big?? even at f6..??
>     Is 14" too big?? at f5     so on , so on.  I have a table top 
> 30"x69" by 3/4" nice green plate glass
> and I want to push the limit. I know It's really thin, ..so is my 
> wallet. Experimentation situation, come on
> guys I need some input.. I am presently grinding two mirrors, one at 
> 9"x 5/8" plate and the other at
> 10"x5/8" plate. Both are at 15micron now and as far as I can see they 
> are  spherical and comming along nicely. I know I need  to finish 
> these before I proceed to the 3/4" but the glass says it doen't want 
> to be
> a table top any more. (I have checked the glass with polirized filters 
> on the rotation and the sweep and
> there is no stress to the naked eye)  I have also scored the surface 
> with a carbide scriber and you can write
> your name on the surface easily.  How big can I go???? Is 16" too big 
> at f6  ???
>                                                                           
> RUSS JOCOY

Personally, I wouldn't go beyond 14" F/5 max with it.  12.5" to 13.1" 
would be a safer bet.

Larry

-- 
My philosophy, in essence, is the concept of man as
a moral being, with his own happiness as the moral
purpose of his life, with productive achievement as
his noblest activity, and reason as his only absolute.

Ayn Rand (in the appendix to 'Atlas Shrugged')