Re: [ATM] Fixing Tom's oblate sphere

["Jerry" <wa4guu@verizon.net>]

Hello again Tom.


What type of tester are you using? Do both the source and knife move or just
one?  I'm betting by the Foucault readings and your Ronchi image that both
move.

I favor full size laps.

If you were fully polished:

You have the best shape you could have for learning to figure! Oblate and
TDE. What are you afraid of? You can always at least get back to this!  So
instead of thinking anything I suggest you do might mess up your mirror,
think "this is just the time to try Jerry's stupid suggestions. What could
go wrong?"


Heee HHEEEE! 

Someone long ago said that long strokes cause TDE. No one bothered asking
any details. It has been repeated so much that if you asked what causes TDE,
More ATM's will have that at the top of the list than any other. So that
makes you scared to try anything that could in any way be thought to be
"long".  Too bad. That leaves out the "classic method" (as labeled by
Texereau). 

The second reason for long strokes after turning the edge is for
parabolizing. They also work for making an oblate into a sphere. You need
some of that.

If you are game but still a little chicken then you could do TOT 5" W and 4
inches wide. If you are brave, you could make a full blown parabolizing W. 

You should work short time and test. If you go long without testing you will
not be in control. Bad things can happen fast. Good thing do too. Good
overdone can be bad.


On a first mirror you might be safe saying that you will have the center
polished by the time you are done. But figuring does not have to take very
long. It is when you get the aluminized mirror back that you see if you
misjudged.  It is very easy to see if the mirror is not fully polished after
it is coated. But you would rather not learn that from personal experience. 



You've done short and you have a TDE. Go figure.

Jerry







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