Re: [ATM] Figuring question

["lance clarke" <alaskawolfjoe@hotmail.com>]

Hi,
Here are the details of my mirror:
diameter= 12.5"
thickness= 1"
focal length=62"
F5
glass = supposedly 96% silica glass (i'm not totally conviced though...looks 
too much like plate)
I'm definately totally polished out.
Pitch lap is soft (now)...it was just right a couple of months ago. Now we 
are in a bit of a heat wave.  However, I've been trying to figure since 
March.  In the cold weather it took about 2 hours for the channels to close. 
  Now, I'm not sure, since I don't do spells long enough to determine this.  
I'm using gugolz 55.
The lap is probably 3/8" thick.

I don't polish until the airconditioning takes the temperature of the 
apartment down to at lease 22 degrees celsius (an hour before I start to 
polish, so some thermal equilibrium can take place)

The took is made of dental stone.

I have been trying to parabolize...should I go back to sphere first now?

Here are the numbers:

zone       radius          reading
1            1.032          0.006
2            2.225          0.029
3            2.844          0.043
4            3.574          0.071
5            3.990          0.079
6            4.505          0.095
7            4.863          0.106
8            5.271          0.123
9            5.600          0.132
10          5.939          0.144

All numbers are in inches, I'm using a slitless tester, and the readings 
were using 2 masks to measure every second zone. I do my analysis with 
Figure XP, and find that I have  a low zone at zone 7, followed by the 
outermost zone being too high.

My attempts to fix this have been to use whatever stroke I'm trying for 
several sessions (about 5 min each) in a row, taking measurements after 
letting the mirror cool for several hours (usually overnight).

I think that covers all of the details.

Thanks for having a look, I'd really like to have this done for Starfest 
this year, but if it takes another year to get things just right, so be it.

Lance


>From: Mike Lockwood <melockwo@uiuc.edu>
>To: atm@atmlist.net
>Subject: Re: [ATM] Figuring question
>Date: Tue, 30 May 2006 12:35:35 -0500
>
>Lance,
>
>lance clarke wrote:
> > I'm at a bit of a loss how to proceed.  Figure XP tells me I have a low 
>zone
> > 1.5" from the edge, and the edge is also high compared the the rest of 
>the
> > mirror. I've tried MOT w strokes, coc strokes, long and medium long (and
> > even short just to see what would happen), and TOT short strokes to 
>bring
> > down the outside...always seems to give roughly the same result.  Is 
>there
> > something I'm missing?  Should I blame the lap?
> > The mirror is a 12.5" F5.  I can post my test numbers if it helps.
>
>Yes, the test numbers (ROC, mask radii, zonal readings, moving- or
>fixed-source tester) would probably help.  Now for the standard questions:
>
>Also, is your mirror Pyrex?
>Are you done polishing?
>Or are you still spherizing or are you working on the final figuring?
>Have you judged the hardness of your lap?
>If not, how long does it take the channels to nearly close during
>normal polishing?
>What type of pitch is it?
>How thick is the pitch?
>What temperature is the room you are working in?
>What is the tool substrate made of?
>
>If you are trying to spherize and you have a classic oblate sphere
>shape (and possibly a turned edge) which can look like a low spot
>about where you describe, then here's a link to my page with info on
>how to fix that:


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