Re: [ATM] ATM Digest, Vol 22, Issue 12

[Hugues.Laroche@ses-astra.com]

Hello Mike,

You said:
>I was just wondering:
>1)  I know no one tracks their time precisely, but how many hours did it
>take you to make your mirror, from course grinding to figuring?

I think THIS depends very much from individual and circumstances.
A skilled glass pusher, single and in holidays could make 
a 8-16" mirror in a few days, I guess, if all goes fine.
For me, always in task swapping,
it takes several months whatever. Well, regarding the true hours
of work, as you said I do not take precise timing.

>2)  Did your second mirror go quicker, slower or about the same?

It does go a little quicker, but it merely goes better, with
less errors and back and forth, provided the mirror size
remains about the same (but frequently the second mirror
is larger than the first one :-).

>3)  Does the grinding time increase exponentially as the mirror gets 
bigger?

Curve generation time, probably more like the square or cube of the 
mirror's size.
That's why it is advised to purchase large blanks already pre-generated.
Apart of curve generation, the grinding time increases slolwy with
size, as I see it. I have ground my 45" (yes) by hand with a 67% sized 
tool, and
apart that extra care for sphericity had to be taken, it went OK till
15 microns grit. Then, for such a large chunk of glass, drag becomes 
large,
and support quality plays a big role, and the end of fine grinding wasn't 
successful which caused some back and forth at polishing. That's where
I am now (and I have switched to machine grinding/polishing =:-) )

Happy ATMing,

Hugues
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