A discussion of cutting a Concave dish into a piece on 
a lathe came up on the list. Some folks were having 
problems imagining the setup without a picture so I put 
one together to help out. Thanks go to Dick McBirney for 
offering the solution to the problem. The particular 
problem specified a 1.5" radius, thus the 1.5" length 
for the cone-ended rod. I made a correction in step 5 
to specify LEFT rather than right. I expect in step 7 
you could cut in both directions, but it was not 
discussed.

Rance


> ----- Original Message -----
If you really wanted to use this for many jobs, a 
ball-ended rod riding in cups would be more elegant.
But I have used this trick to make spherical faced 
washers and mating spherical faced adjusting bolts 
for my Colchester, and poking the sharpened
rod into the paint works fine.

Dick McBirney 


> ----- Original Message -----
From: "dick mcbirney"
Subject: RE: machining teflon

1) Cut a steel rod to a length of 1.5", turn a 60 deg cone
point on both ends without shortening the rod.

2) Set the lathe compound rest to 90deg - parallel to
bedways.

3) position a toolbit right on the centerline at the center
of the work.

4) hold one end of the pointed rod against the cross slide
with the rod parallel to the bedways, then slide the
tailstock to the left until it hits the other end of the
pointed rod, lock the tailstock down so it holds the rod.

5) turn the lathe on, advance the compound to the LEFT
until the bit cuts.

6) feed the cross slide out toward you while using the
carriage handwheel to maintain contact with the left end of
the rod. As you feed out, the rod will pivot around its end
that is touching the tailstock, allowing the carriage to
move to the right in a circular arc as the cross slide
moves away from the center of the work.

7) run the tool back to the centerline, advance the
compound and repeat.

Dick McBirney