Re: [ATM] Stubborn TDE

[Mike Lockwood <melockwo@uiuc.edu>]

David,

David Steinhauer wrote:
> I've been trying to get rid of the TDE in my 6" f5 mirror, without
> success. So, to summarize, my original Ronchi and KE photos look
> the best of all.  Until I started working on the TDE, I would cold
> press for a while and then do long 1-hour polishing sessions with
> no cold pressing in the middle.  I realize now that that was too
> long, but even so I still managed to get the best figure so far.

That is a very telling statement - it indicates that during your 
longer work sessions you finally got your best contact between the 
pitch and the mirror.  In my experience, TDE is often caused by poor 
contact, and sometimes it's hard to distinguish that by how the lap feels.

> Any ideas on what I could be doing wrong?  How much downward
> pressure should I be applying?  I tried doing MOT, but that also
> didn't get me anywhere at all.

First, please tell us how hard your pitch is.  The easiest way to 
describe it is to tell us how long it takes your pitch channels to 
close (or require serious trimming) during normal polishing.  6 hrs is 
too long.  30 minutes ot too short.  2-4 hrs is best, in my experience.

Second, please describe your polishing stroke.  I like to use moderate 
polishing pressure, which is still probably 15 lbs of downward 
pressure.  This depends on how the pitch is behaving, however.

Last, please tell us what the mirror is made of (plate? Pyrex?) and 
what the tool substrate is (what the pitch is poured on).

	Mike Lockwood

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