Re: [ATM] Figuring questions on a 6f6.

["Shane LaPierre" <shane@ct-astronomer.com>]

I would do a 1/4 W stroke ToT.  It will tend to flatten 
overall.  I do this when my overall correction is off. 
 Keep the stroke short (1/3 is total is probably too much) 
 less than 1" each direction is ideal.

Best wishes,
Shane LaPierre

On Tue, 9 Oct 2007 09:19:29 -0500 "Anthony Anconetani" 
<Anthony.Anconetani@genband.com> wrote:

> Good morning guys,
> 
> Well, I'm trying to decide where to go next in figuring 
>my 6F6 mirror.
> Before I do anything rash, I think I need to consult 
>with the experts.
> 
> The ideal measurements in FigureXP are 
> 
> 0.000
> 0.0019
> 0.0038
> 
> The room temp is 85-87 degrees (still hot in Texas). The 
>tool is full
> sized with G73.
> 
> 
> After about three hours of polishing I checked the 
>figure. The edge
> looked good and the mirror looked spherical. I decided 
>to do another
> hour of polishing to be safe. I then checked the figure 
>again made the
> following measurements:
> 
> 1: 0
> 2: -0.014
> 3: -0.023
> 
> I decided I was high in the center but I knew that would 
>be easy to fix.
> So decided to try some parabolizing.
> 
> I did 10 minutes of MOT using the parabolizing stroke. I 
>tried modified
> the stroke to do some extra work around Z2 and Z3. Here 
>were the
> results.
> 
> 1: 0
> 2: 0.043
> 3: 0.045
> 
> I was a little surprised at how much I actually took out 
>of the center.
> I'm guessing I went to far to the left and right. 
>Anyway, I decided to
> go with a basic 1/3 COC TOT stroke. I figured this would 
>reduce the
> correction between Z1 and Z2 and would reduce Z3. Ten 
>minutes of 1/3 COC
> TOT gave the following.
> 
> 1: 0.000
> 2: 0.036
> 3: 0.060
> 
> I was happy with the reduction in correction from Z1 to 
>Z2. I also
> noticed that Z1 had a smoother transition from it's 
>inner edge to it's
> outer edge. However, I was really surprised to see the 
>delta from Z1 to
> Z3 increase. I thought the TOT would have a tendency to 
>flatten out the
> mirror. The above indicates the center became deeper.
> 
> I mulled this over for a while and decided to try 
>another round of 1/3
> COC TOT. My guess was that Z3's increase relative to Z1 
>was a temporary
> dynamic in the glass. I think was wrong. Here are the 
>results of 10
> minutes 1/3 COC TOT:
> 
> 1: 0.000
> 2: 0.053
> 3: 0.088
> 
> Well, I'm thinking COC TOT is not a good idea at this 
>point. I'm just
> really surprised that the center got deeper.
> 
> So questions:
> 
> 1) Why did COC TOT deepen the center?
> 
> 2) Since COC TOT does not appear to be reducing the 
>outer zone, how
> should I reduce the outer zone? A narrow W stroke with 
>1/2 diameter MOT?
> Or maybe a wide W stroke with 1/6 TOT? How about a stick 
>of dynamite...
> 
> Thanks,
> 
> -Anthony, Round Rock TX.
> 
> 
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