Re: ATM Re: [atm_free] Stubborn 1/2 " edge zone

["Jeff Anderson-Lee" <jandersonlee@sbcglobal.net>]

From: "Russell Jocoy" <russjocoy@hotmail.com>
>      Jeff,         I don't know a whole lot but if you have a central
"hole"
> and the outer 30% of
> the mirror is kinda flat, then the flat area is the way to go to the
> parabola. Work the glass backwards
> to the center, since the center is already where you want it to be. The
> worst that could happen
> would be returning to a sphere if you over shoot..   or a TDE, or
> something...  You cannot hurt
> the figure that you now have because it needs to be changed. If you change
> it into something
> ugly, that too can be changed. You are working with microscopic movements
of
> glass on the surface
> that can change in 10 strokes, if you are doing it right.

If only that were the case.  There's still quite a difference between the
two zone radii.  If ten strokes made a difference then the 1.5 hours of TOT
1/3 COC should have brought me back to a sphere by now, but it didn't.

>From the perspective of the outer zone, I have a large central hole.
Relative to the inner zone, I have major TDE.  The minimal amount of glass
to move/remove would seemingly be if I attack the edge of the zone
boundaries and spread that both inward and outward to come to a compromise
radius.  I just don't know what stroke to use to accomplish that.

> Experiment at
> small intervals and remember
> that you are at a point that polishing can't harm the mirror, just change
> it's figure.

Unfortunately I don't have a great testing setup.  At home I have to coopt
the entire kitchen to work and then still have bad air currents.  At Chabot
I have to stand in line for the tester which wastes about 20-30 minutes for
each test.  Thank heavens I'm (mostly) a patient person.

> That is unless
> you sprinkle some 220 grit on your lap....... This is not advised by the
ATM
> association of the world
> according to GARP.   the GENERAL ASTRONOMICAL REFLECTOR PRINCIPAL.......

I already did that on one mirror.  Fortunately it was only at 17u and not
polished out.  Back to 400 grit on that one.

Jeff