From: "Jean-Guy Moreau" 
To: "Frank Ward" 
Cc: 
Reply-To: "Jean-Guy Moreau" 


Thanks a lot for the reply, i could have been more specific with my
question, it was really about general polishing,
 but i am very happy with your detailed description
of  "pushing the glass up the hill" i will definitely try that on
the current mirror (18") if i have to climb up a hyperboloid.


My technique right now is simply to polish more with the normal COC to 1/4
overhang with 60% lap but it takes a long time to completely polish the
extreme edge.

Large laps put quite a strain on my machine, that's why i am interested in
60% ones. I mostly end up with a nice spherical surface, but with a
seemingly high zone about 1" wide at the edge, from lack of polishing.
I know the edge is not really turned as i can plainly see the diffraction
ring on the knife side.

Do you parabolize with your machine ? if so i would be very happy to hear
of your techniques, and so would a few others i am sure  ;-)

Thanks again,

Jean-Guy



 I put the work surface on the rotating disk (25 rpm)
> and after preparing the tool, place it on top. I hold the tool
> in my hands, not attached to the overarm, and make my strokes
> thru the center of the work surface without a lot of overhang.
> The pressure from my fingers attempts to "lift" the tool
> as it returns over the edge again to avoid turning it and
> pushes down when it is "going up the hill". Every six or eight
> strokes I go out to the sides a little to keep the surface
> blended. When I do this I am using the normal parabolizing stroke
> but in reverse. That will lower all the numbers so I am very
> careful to use it sparingly.

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