[SENT] ATM 1st mirror - machine use

[PFAFF2@delphi.com]

>> 
> I'm done with 320 grit on my 6 inch, f/3.67 and will proceed to finer 
> grades.  I'm using a grinding machine and have 20 lbs on the arm 
> to speed grinding.  As I go to finer grits should I:
> 
> 1.  Reduce the weight, and to what value?
> 
> 2.  Are stroke size/shapes different for machine work versus hand 
> work?  (I'm using TOT, 1/4 strokes in a "W" that provides about 3/4" 
> overhang at each side of the "W.")
> 
> 3.  Go to hand work at a certain fine grit?
> 
> 4.  Could I even polish by machine?  Maybe for the first few hours?
> 
> Thanks in advance!
> 
Thanks to Randy some of your questions may be answered.
For fine grinding a total weight of a pound or two should be
enough. The weight of the tool and pin may be enough.

As to the stroke machine work is different then hand work.
You want the pin to move from the center of the table to the left
of the table by 1/4 diameter of the mirror. Do not swing to the right.
That means you will have a 1.5 inch overhang over the left side at the
end of the stroke. ( assuming the table is turning counter clockwise
and a full size tool)

Yes you can figure a mirror with a machine ( well almost :-)
I got my 24" f4.5 in the ball park anyway.
I used a 50% tool with a star like edge. Final touch up by smaller
subdiameter hand  tool. The tool overhand and stroke is critical
when machine figuring with a sub tool so keep a good log.

There is a write up on what is called a quadrant lap for machine figuring
very fast mirrors like f4. Ritchey was said to have used this kind of lap
at times. I have not tried it. Anybody ever tried it out there?
See Sky and Tel Dec. 1970.

The lazy glass pusher
Bob Pfaff