Re: [ATM] Turned Down Edge

["Jonathan Bishop" <jonathan_bishop@sbcglobal.net>]

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


----- Original Message -----
From: "Rich Ball" <ShooterBall@hotmail.com>
To: "ATM List" <atm@atmlist.net>
Sent: Thursday, July 15, 2004 12:40 PM
Subject: Re: [ATM] Turned Down Edge


> Ergo:  in most instances the phenomenon referred to as TDE results not
from
> an edge actively being turned down but from its never having been Turned
> Up... so to speak.
> The nomenclature can be misleading, no?
>
>
> > Assume that you start off with a PERFECT SPHERE...
> >  If you then work the center of that sphere, Which is
> > what you are doing when working MOT, the center will
> > become deeper and will have a shorter ROC... >
> > Ken Hunter
> _______________________________________________
> ATM mailing list http://www.atmlist.net/

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