>> Anyway I see no reason for every ATM to reinvent the wheel. I will write
>> a few posts (about one per week) on how I made my plates along with the
>> problems that were encountered using the vacuum method.
^^^^^^
> I've got a general question about making corrector plates. I've always
> wondered if it would be possible to bypass the vacuum fixture and instead
>use
> blocking pitch to attach a suspended weight from the center of the blank. It
> seems to me that it should come close to the correct deformation depending on
> where you support the glass. Anyone know if it would work?
Unfortunately, the answer is NO. The plate deforms differently when pulled at the center from what happent when it is uniformly pressured by the atmosphere. Try any finite analysis program, and you'll see.
Anyway, the vacuum method is only effective for moderate f/ratios - the shape will be only an approximation of a complex curve. Also, it is useless if your blank is thick (like my Wright - almost 1/2" for a 6"). Another thing is that it won't be good for high quality work (say, visual scope) because you will grind/polish in all the errors of a vacuum pan (something finished on a lathe hardly qualifies as an optical surface !).
Bratislav