Re: [ATM] Newbie needs help getting to sphere...

[Kevin MIchael Zabbo <chaosopher23@yahoo.com>]

SiC is great, but don't worry about a sphere yet. 
Instead, try a 4/5 MOT to get your radius of curvature
and then go to 120 to get it closer.  After 120 gets
you in the ballpark, go center-over-center with 120 or
finer until it sticks pretty evenly when you push.

When you get to polishing is when you worry about the
figuring, and you can really only tell if it's a
sphere if you have it on a testing bench.

To tell if your grit is eating glass uniformly, draw a
spider web or any cool pattern on the glass with a
waterproof marker and grind it off.  Sharpies and Sir
Marksalot are good candidates for the job.

Kevin of Eastern Iowa
Seeker of the (Southern) Darkness

--- Graham McGuire <mcgugrah@hotmail.com> wrote:

> I have been grinding with 80 SIC and 1/3 MOT to try
> to get t sphere... but 
> after twenty hours there is
> 
> still a hole and I am 6" long on my FL. I started
> with a chordal and as 
> Richard Berrys book suggested and
> 
> carried on with above after I reached 60"... after
> ten hours the sag of my 
> 6" mirror is .041 (close to the
> 
> .047 req'd for the f/8, 48" I am aiming for). Help!
> its driving me insane 
> that I still have a .75 " ledge
> 
> around the mirror.
> 
> Cheers,
> 
> ~Graham McGuire esq.~
> 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


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