[ATM] re:Parabolizing

[Bill Marriott <bmarriott@pacbell.net>]

Bryan;

Looks like I'm first up this morning, so my 2 cents is that the bump is 
not a bump, but indeed the start of the parabolizing process. That area 
should expand and work its way to the edge with time, though in sneaking 
up, you would like the correction to take place over the whole mirror.
Try shortning your stroke a bit, or do some center over center once and 
a while to spread that corrected area out. You do not want your 
'corrected area to turn into a hole, deeper than the final figure will be.

Ask more questions here, sounds like you are on the right path.

Bill Marriott
VA Optical Labs
http://starlightoptical.com

Bryan Stiles wrote:

 > Good Morning Everyone, I have a newbie question (again). I am working
 > on my first mirror (8" f/6) and have just begun the figuring stroke
 > with the MOT. I am using a pretty thin CeO mix. Contact seems very
 > good and there is a nice smooth friction to the movements.
 >
 > Trying to sneak up on the correct figure, I worked about ten minutes
 > and removed the mirror to see where I was. I placed the mirror on the
 > (foucault) test stand and had a look. What I saw was a small bump
 > (1.5"-2" dia) in the middle of the mirror. The remaining surface
 > seemed to be left at the sphere (since it darkened evenly at the ROC).
 >
 > After seeing that I wondered what was going on? So I warm-pressed and
 > began working again MOT (after everything cooled down). Another
 > ten-fifteen minutes of work and had another look. The bump was larger
 > (2.5"-3.5" dia).
 >
 > Afraid of what I might be doing to my mirror, I stopped for the night
 > to let everything cool down and ask for help in figuring this all out.
 >
 > After looking at the mirror this morning, the image is the same. I
 > switched over to a grating and had a look inside and outside of ROC.
 > The image seemed to indicate that the bump is a something different
 > (parabola?) than the remaining surface. The lines on the remaining
 > surface stay nice and straight while moving back and forth.
 > Conversely, the lines on the bump bow and roll with movement.
 >
 >
 > The theory that I'm working with is that the bump is actually the
 > progress of parabolization moving out to the edge of the mirror. That
 > leaves the remaining surface as a sphere.
 >
 > I would sincerely appreciate any guidance you could provide.
 > Bryan Stiles
 > _______________________________________________
 > ATM mailing list http://www.atmlist.net/
 >


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