Re: [ATM] Not tde or tue, important oblate spheroid, ellipsoid

["Thomas Janstrom" <thomas@moiler.com>]

Um, as I was the one who first posted that response, let me elaborate....

The CoC stroke I use is 1/3 D with no over hang on the back stroke (i.e.
there will be 2/3 of the mirror radius over hanging on the "side" away from
me at the end of the stroke, but on the return I stop before there is any
over hang) and it is dead centre over centre. This always gives me a great
sphere that is very smooth. I will say that the stroke length is varied a
little all the time (this is due to my not being a machine), but the average
is 1/3 of the mirror diameter.

Also I work seated on a bench with the grinding platform in from of me, I
rotate tool and mirror every 6-10 strokes in opposition to each other a
random amount....

Cheers, Thomas.

Sorry about the delay, but I had to check with my grinding/polishing (one
book per mirror) logs to make sure I wasn't spouting the proverbial.....

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Jerry
Sent: Thursday, 3 January 2008 10:58 AM
To: 'Mitchell R'; atm@atmlist.net
Subject: Re: [ATM] Not tde or tue, important oblate spheroid, ellipsoid

With a full sized well pressed normal lap with uniform facet size (not
graduated or trimmed into petals) I think Jim has accurately predicted the
result. How do you do the 1/3 COC correctly that makes the sphere. 

Weren't you fighting persistent oblate spheroid with your 6" until you put
some side motion (W) into the stroke? Were you watching the turned down edge
so intently that you missed what else was going on, or did you adjust your
thinking of the definition of COC to include "near COC W strokes"?

I'll bet you adjusted your definition of COC to fit what made a sphere for
you.

Jerry


[Comment 1) was from Jim Burrows]
-----Original Message-----
From: Mitchell R
 

A couple of things:

1)  Theory says that any COC stroke, MOT or TOT, pushes the mirror 
surface further into oblate spheroid territory.

I am confused. 1/3 COC is a standard stroke for most. As long as I am doing
it correctly it brings nothing but beautiful spheres. Even moves an oblate
to a sphere. ?

Mitch



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