Re: [ATM] Turned Down Edge

["Scott Ewart" <scott.e@quicksurfer.com>]

Jon,
    It does sound like your problem was indeed caused by soft pitch.  But
you might be surprised how steep and narrow an edge can get the other way,
even when the stroke takes the lap beyond the edge.  I suppose this is more
common with under-size tools.  But the two can be hard to tell apart.
That's one of the things that make them so sinister.

Scott


----- Original Message ----- 
From: "Jonathan Bishop" <jonathan_bishop@sbcglobal.net>
To: "Rich Ball" <ShooterBall@hotmail.com>; "ATM List" <atm@atmlist.net>
Sent: Friday, July 16, 2004 1:22 AM
Subject: Re: [ATM] Turned Down Edge


Hi,

I think we are talking at cross purposes here. When I think of TDE I am
thinking of a very narrow zone, say 1/4", at the edge of the mirror which
has a dramatically longer radius of curvature than the zone next to it.

I suspect the most likely cause of this is the mirror digging into a too
soft lap. That is what I believe to have caused the problem in my case. So
the "cure" was to switch to a harder lap and do short COC MOT strokes.
Without getting a harder lap I just could not fix this TDE no matter what
stroke I tried.

What I hear being discussed in this thread is a zonal defect caused by
selective polishing. For instance deepening the center and leaving the edge
alone. I think that in this is better referred to as a zonal defect.

I think it would be difficult to produce the narrow severe TDE I did by
polishing the mirror everywhere but the outer 1/4"!

Although I think we have some on this list who are capable of doing even
that :-).

Jon Bishop


.net/

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