Re: [ATM] Mirror figuring problem

[Aplanatic@aol.com]

Howdy,
 
Four zones is not really enough to get a good idea of the mirror's profile,  
especially when one of the zones is the central area.  May I suggest that  you 
make a new set of masks with five zones?  There's no reason at all to  
measure inside a radius of about 1 inch on an 8" mirror.  So,  start the inner edge 
of your new zone 1 somewhere around an inch and avoid the  headache of trying 
to null the center of the mirror.
 
When I work TOT with short strokes on a small mirror I always get TUE, a  
slightly oblate figure and mild to significant astigmatism.  So, I'd work  the 
mirror MOT, 1/3 strokes with a slight V for a half an hour and see what  
happens.  By now the lap should be in very good contact.  If it's not  remake with 
tempered pitch, press really well and have at it.
 
What fun!

Good luck,
 
Dave Rowe
 
In a message dated 1/2/2006 7:59:14 P.M. Pacific Standard Time,  
cjkreutze@comcast.net writes:

I am  figuring my first mirror and have been trying to work out a problem for 
a  while now.  I am sending out this email as a distress signal since I can  
not seem to solve my problem.  My problem is that my mirror has a  depressed 
zone at around the 75% radius (and a TUE).  Here is the  necessary foucault 
information: 8in mirror, full thickness.  ROC:  90.125in.  I am using a slitless 
moving source tester (Stellafane tester)  with the Couder mask suggested in 
Texereau Fig 2-32 p. 77 (4 zones).   Here are my most recent zone readings 
(average of 4, all readings are within  0.006 of each other).  
Zone 1: 0
Zone 2: 0.025
Zone 3:  0.054
Zone 4: 0.049
Effective mask Radius: 0.854, 2.028, 2.96, and 3.654  (From Figure XP)
I have been working for a while now using the normal  stroke to try and get 
back to a sphere and remove the depressed zone.   Unfortunately, while my "Best 
Fit Conic Constant" is moving closer to a  sphere, the depressed zone is not 
improving.  I was hoping to use the  normal stroke until I removed the 
depressed zone and came back to a sphere but  unfortunately, I am almost positive 
that the zone will not go away with my  current technique.  
Here is some additional information that might  help: I am polishing 
exclusively TOT with a full sized lap and a sheet of  cabinet liner underneath the 
mirror to keep it from moving.  
Any  seasoned vetrans out there have a minute to help out?   

_______________________________________________
ATM  mailing list http://www.atmlist.net/




_______________________________________________
ATM mailing list http://www.atmlist.net/