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Re: ATM 5 Micron or not 5 Micron?
Mike Coslo wrote:
>
> I am almost finished with the fine grinding phase of a 12.5
> inch pyrex mirror.(my first) Everything is going well. I just
> finished the 9 micron wets, and I understand there is some
> contention regarding going to 5 micron or starting with the
> polishing stage after 9 microns.
>
>1) Will skipping 5 micron wets add appreciably to the
> polishing times?
If you can successfully pull off a good 5u grind, without scratching,
and polishing out your 12.5" by hand, you may save a couple or more
hours of ooomph time, and you'll have to put a lot of time into
polishing anyway....
>
> 2. What do/did you do?
In our optical shop, Pyrex grinds very nicely with 5u, especially with a
little propylene glycol added to the water, slows down grinding rate,
but very smooth surface...
Over at the Chabot College Telescope workshop, we tend to suggest a 9u
finish, as its easier to produce a nice scratch free polishable surface,
especially in that battleground, where we have grinders and polishers in
the same room, although on seperate tables. If you have a place where
you can be obsesive about cleanness, give it a go, as you can always go
back to 9u if scratchs are not toooo deep.
It doesn't take that much of a particle to cause a scratch, when the
abrasive size is approx. .0002" .
If you decide to try 5u, keep your grit thick and fresh, if it thins out
too much you may hit bottom 8+(
> 3. Pads or no pads?
Pads also can knock some time off the polishing cycle, especially with
hand polishing. They're good for polishing out the 'grey', and I have
seen
work out well in terms of a fairly spherical surface, ready for some
quick cleanup with pitch before parabolizing, but have seen several
disasters
as well....
>
> thanx, - Mike -
--
Bill Marriott
Woodacre, Ca. USA
btk@pacbell.net
http://www.starlightoptical.com
Optical/ATM projects
And, now, P1800 Volvos
http://www.starlightoptical.com/volvos.htm