From: "Herb Kasler" 
To: "Jerry B. Hillman" ,
        
Reply-To: "Herb Kasler" 



Jerry,


Based on what I've seen on your last ronchigram, I think you're getting
quite close. Your edge might still be kind of low, but I think you might be
able to blend out all but the outermost 1/8" or so of it. It's
definitely MUCH better than it was before. All you have to do is dig out
the center a little more, while working the whole surface down towards the
edge. That is the easiest thing there is to do.

I am a bit confused about your stroke, though. You keep saying in your
posts that you're going COC. That's not really the stroke you should be
using, IMHO. What you should be doing is a "wWw" stroke, with
short strokes out to the side and longer strokes in the middle, so that
your tool overhangs maybe 1 to 1-1/2" both to the side at maximum
lateral displacement and at the ends of your strokes. No overhang at all is
kind of dicey, because you risk creating a zone in the edge area that's not
getting any action. Plus you need to put take some glass off your 70-95%
zone in order to blend out your TDE. If you concentrate too much work in
the center, it will actually make the TDE worse. The point is to smoothly
taper the action to the edge, rather than abruptly halting it. It is
therefore better to make a more tapered star and still overhang some,
rather than stop at the edge of the mirror. I actually think the star lap
you posted looks pretty good for the mirror you have.

Also, to avoid digging any zones, you should put hand pressure only in the
center of your tool and push it back and forth by its edge. What I did was
rest the palm of my left hand on the center and push down there. I pushed
it away from me with the fingers of my right hand on the near edge, and
pulled it towards me by hooking the fingers if my left hand over the far
edge, while maitaining pressure with my palm. I'm left-handed, so if you're
right-handed you would probably want to do it the other way around.

Good luck,


Herb.

--- BBBS/NT v4.00 MP