Re: [ATM] Blank ratios for different materials.

["Vladimir Galogaza" <vladimir.galogaza1@zg.t-com.hr>]

Hi Anthony,

>I think the ratio for a Pyrex blank is something like 6:1. Is that
>correct?

It was, many years ago, by the way of consensus. Today this is history.


 >And, what would be a good ratio for materials like plate glass, BVC and
>Quartz?

Most ATMs have made too little number of mirrors with different diameter-to
-thickness-ratio, to get any meaningful statistics out of their own 
experience.
Since technology of thin mirrors has developed  relatively recently, 
especially
mirror support part of it (PLOP), what was difficult years ago is widely 
available
and used today. "Playing safe" is not much valued approach with ATMs, more
likely is "pushing the envelope" approach. For those people there is 
probably
no such thing as "good ratio" , instead they debate about  "possible ratio".
Experience with quartz and other low expansion materials like Sital and 
Zerodur
must be scarce within ATM milieu. At least I can't remember anybody claiming
to start with quartz blank and reporting that it was to thin for finishing 
it into
successful mirror. And even this depends on individual skills. How can then
such person know and advice on "good ratio".
Perhaps one information can be inferred from factories in China producing
hundreds of mirrors for OEM. They will  very likely optimize their 
production
around certain diameter to thickness ratio which will give best economy
( material price, production difficulties, labor force skill, quality 
control,
OEM  requirements, to mention some) but none of those things is of ATM 
concern.
We are not facing market forces but checking our own limits of skill, 
endurance
and imagination.

Regards
Vladimir. 

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