Re: [ATM] Fixing Tom's oblate sphere

["Polk, Tom" <TPolk@decatur-al.gov>]

Tom Polk
>SNIP<
IF the mirror were fully polished...
**** On a scale of 1 to 10 (10 being full polished) the center, ~2.5"
dia., is a 9+, the balance = 10. No doubt after I get this corrected,
the entire surface will be a 10.

>SNIP<
The 4-5 Ronchi shows raised intermediate zone has become more of a
raised
center and the hole that was in the center of the wide hill, has
disappeared. The mirror looks to be more oblate. The curve is a smoother
oblate. And the TDE may be worse.
**** One good thing from all of this is that I can read Ronchi-grams
better. Comparing it to a Foucault test helped. I had the time to
conduct a Foucault test yesterday. Here are the results:
Units are in Inches 

Mirror Diameter = 12.5 
ROC = 136.69 

Moving Source Tester:
 Zone 1 radius = 1.2782	 
 Zone 2 radius = 2.4145	 
 Zone 3 radius = 3.1247	 
 Zone 4 radius = 3.6983	 
 Zone 5 radius = 4.1935	 
 Zone 6 radius = 4.6358	 
 Zone 7 radius = 5.0392	 
 Zone 8 radius = 5.4126	 
 Zone 9 radius = 5.7618	 
 Zone 10 radius = 6.091	 

1 Readings = 0 		-0.002 	-0.001 	-0.005

2 Readings = 0.003 	0.001 	0 	-0.001

3 Readings = -0.003 	-0.004 	-0.005 	-0.004 

4 Readings = -0.012 	-0.011 	-0.013 	-0.012

5 Readings = -0.02 	-0.019 	-0.02 	-0.019

6 Readings = -0.03 	-0.029 	-0.029 	-0.028

7 Readings = -0.041 	-0.043 	-0.042 	-0.038

8 Readings = -0.05 	-0.051 	-0.051 	-0.048

9 Readings = -0.056 	-0.057 	-0.057 	-0.053

10 Readings = -0.04 	-0.04 	-0.041 	-0.039

Gee, that is a lot of glass to get out of the way.

>SNIP<
With the smooth
oblate that you have now, the base of the hill would be at the mirror's
edge. Wearing the center fastest would be MOT. This would shorten the
radius
of curve at the center to come to match the short radius of the outer
zone. 

A TOT alternative wears the outer zone to a longer radius to match the
longer radius of the raised center. And the idea here would be to find
the
stroke to wear the edge the fastest and dropping to slowest at he
mirror's
center. You find the right length stroke, this will fix the edge too.

The oblate shape suggests scaling up the size of your W. Say 5 inch
stroke
length and a 4 inch wide W. that would be 2 inches to each side.

**** Use this stroke for either TOT or MOT? 

If it were me, I would pick one or the other... either MOT or TOT and
stick
to it for a while. There are a couple of reasons I can think of. If you
do
more than one thing at a time, when something works, you won't know what
component of your various strokes did the deed. One of those may be
taking
the TDE out, and the other putting it back in. One could be working
perfectly and you wouldn't know.

That the center wasn't polihed would suggest that you should use MOT.
But
the TDE might best be worked TOT. 

You could go different ways here. The key is whether it is fully
polished.


Jerry

**** Thanks for the in-depth reply and all the others. I know it takes
time to analyze all the information submitted, consider a reply and post
it.

There are three corrective methods I'm considering:

1. MOT; long strokes (~ 5"), 4" wide. The mirror edge may be a lost
cause.

2. TOT; long strokes amplitude = ? 5", width = ? 4". Should this stroke
be longer? Might save the outer 3/8" (I hope it gets this small).

3. Use a 1/2 D tool. Still working on this but considering a "normal
parabolization" stroke with minimal edge work or a "W" with a tighter
center stroke with minimal edge work. Smooth out with full sized lap.
I've got one made up with a new lap, #64. The weather here will be
warmer so I can increase room temp to about 73-74^F for a softer temper.


Does method #3 sound any good?

Thanks again for everyone's time.

Tom Polk




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