Re: ATM Central Hill

["Richard Schwartz" <richas@earthlink.net>]

When you use short strokes to correct a TDE, you always end up with a
central hill.  However,  you have made real progress, because a central hill
is easier to get rid of that a bad edge.

Try to visualize that the edge of the lap is doing the cutting.   If you
polish to one side so that the center of the mirror hangs over the edge of
the lap, you will quickly see this: your central hill will start to get a
hole in the top like a volcanic crater.  The edge will not be very much
effected.

Ultimately, you will want o return to 1/3 W strokes to sort of average out
all of the zones and smooth the surface.

So fear not; what you are experiencing is normal!   You are closer than you
think.   By the way, I do not know your location, but if you are anywhere in
southern California, I will be happy to come over and help you get it right.

. . . Richard

----- Original Message -----
From: "Myers, Alan" <AMyers@IKON.com>
To: <atm@shore.net>
Sent: Monday, December 18, 2000 9:38 AM
Subject: ATM Central Hill


>
>
>   I am having great difficulty with my first mirror. It is a Pyrex 8"
f/6.7.
> After completion of polishing, I had a TDE. After searching the archives,
I
> found a recommendation to use 1/3 or less COC strokes. This worked after
> about two hours of work. But now I have this large central hill from the
> center to approximately the 70% zone. The archives suggested a short W
> stroke TOT. I have tried this for over 1.5 hours and can see no change at
> all, except that of the edge trying slightly to turn. I also have tried
> using the standard polishing stroke, but this is seemingly having no
effect
> either. I am frustrated and confused, please help. Thanks A lot.
>
> amyers@ikon.com
>
>
>