Re: [ATM] Stubborn Oblate Spheroid.. update

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

Nice work Jason, and excellent Ronchi images.  Keep going.

Guy Brandenburg wrote:
> I am positive that Peter is mistaken. You do indeed
> have TDE, not TUE. The easiest solution for that is to
> take VERY short strokes for a good long time. Press of
> course, and check again about every half hour.
> Otherwise, the overall figure looks nice and smooth.
> The oblateness gets fixed later, once the TDE is
> fixed.

If it is indeed TDE, short strokes will work (probably TOT).

If you are not polished out, simply keep polishing with normal length 
strokes, working both MOT and TOT and it is likely you will simply 
polish it away.  It is left over from the oblate sphere figure.  Keep 
an eye on it and make sure it keeps going away.

Many think TDE is usually caused by soft pitch.  While this is 
sometimes the case, though, it is my theory that the TDE due to an 
oblate sphere (as shown on my web page) is the most common.  This TDE 
is often leftover after the oblate is long gone!  At least, that's the 
TDE I see most often.

As far as checking for pits, I like a 10x loupe.  Set the focus for 
the surface of the mirror (using another flat surface if necessary), 
shine a light on the surface, and inspect.  This way you can't mistake 
the next layer of glass (in BVC) for pits because you're not focused 
on it.


Jason, when you get ready to start figuring, read my short article on 
figuring with a full-size lap that is posted at:
http://bi-staff.beckman.uiuc.edu/~melockwo/mirror_making/full_lap/full_lap.html

I know that I say F/5-F/8 is the range that I'm talking about, but 
that is conservative and you can likely get there with and F/4.3.  If 
your pitch is fairly soft the techniques in the article will work.

Beware - at first during figuring it may not look like much is 
happening, but really it is.  Just keep going, and test carefully.

	Mike Lockwood

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