Re: [ATM] Re: Hyperbola and TDE - Tenacious

[Mike Lockwood <melockwo@uiuc.edu>]

Jay,

Sorry to jump in in the middle of this thread, but I had some questions.

J Killea wrote:
> Thanks, Bob and Jim, for the guidance on this mirror figuring.  I
> have kept at the short half-stroke to continue reducing the TDE,
> since it was moving things in the right direction, but last night I
> went about 3 times around the barrel doing this and all I got was
> an increase in the amplitude of a a central hill and the zones
> surrounding it, and about 35% deeper TDE than before (total TDE
> deepening of about 15nm).
> I'm thinking that TDE at the edge is fairly stubborn at this point,
> with this stroke, and am considering a couple of possibilities for
> my next stroke (advice is sought here!) :

Well, at this point things aren't working as expected.  So, I'll ask
some questions about your lap and mirror.

It's an 8" F/6 mirror.  What conic constant did you measure?  Was it
really -2.513?  (I wasn't sure how to interpret the SixTests data in
your previous post.)

How long does it take the pitch channels to close when you are doing
normal polishing?

How much pressure do you exert (downward) when polishing?

> a)  warm press and some short COC (don't know if TOT or MOT is
> preferable), or b) warm press and continue with short half stroke
> (TOT) maybe closer to 1/3 overhang instead of 1/4 overhang that I
> was doing.
> Is a warm press useful for the half-stroke technique?  Since it's
> only the lap's edge that's really getting worked with that stroke I
> wonder if great contact all around is necessary.  Anyway, I was
> getting a fair amount of sticking/skipping last night with that
> half-stroke - probably due to the zones.

All this depends on the pitch hardness.  The sticking/skipping is a
sign of bad contact, and is probably not due to the zones.

Again, I don't mean to interrupt the thread and interfere, but I think
some of the basic variables at play here are unknown at the moment.
(Or I missed an earlier post.)

	Mike Lockwood




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