ATM Quadrant Lap

[Bill Marriott <btk@pacbell.net>]

Hi folks;

I am trying to find out some information about quadrant laps.
They have been used in the past at Tinsley Optical, and also by Paul
Zurakowski of the Chabot Workshop, though it has been a very long time
since he has worked with one.

Basically, it is a quarter circle piece of pie shaped lap, which works
like a sub diameter lap, and supposedly gives good control of a curved
or flat work piece.

Paul says he wrote an article about such in S&T back maybe in '71 or so,
and defers to it as to specifics....

If someone out there has access to either the index for S&T, or the
article it self, what I'm searching for is:

1) What is the ratio of the circle of lap to the size of the mirror.
i.e. for a 12" mirror, would one use a 12" quad, or a 10" say?

2) What would be the ideal placement for the pin? 50% zone, 70% zone?

Anyway, I'm getting ready to try to parabolize a 12.5" troublesome
mirror, that I went from being a good 1/4 wave under corrected to being
totally butchered, and took forever to get back to a sphere. (Only
because I kept trying to take short cuts, finally made a new full size
lap, and after 6 hrs on a machine with the Jerry Logan/Bob Pfaff stroke-
eccentric setup, now is a wonderful looking sphere) and thought that
this might be a good case to experiment with parabolizing on a machine
with the quad lap.....

Any help digging up the needed information would be greatly appreciated,
it'll be a week probably till I can make it to the uptown library with
the S&T microfiche....

TIA

Bill


-- 
Bill & Tracy Marriott
Woodacre, Ca. USA
btk@pacbell.net

http://www.starlightoptical.com
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