Chris wrote:

Does anybody have some recommendations to make re tool geometry for
spherical turning on the lathe? I've found lots of designs for ball
turning attachments on google, but nothing so far that describes rake
and tip angles etc.

I bought an attachment, and it came with a HSS tool - very sharp,
symetrical tip, lots of back rake, lots of end clearance. It sort of
works, but the finish is pretty rough and it has a tendency to dig in a
bit, too.


Not having a ball turning fixture or CNC on my lathe, I did it on the mill.
But, the procedure is about the same. I made a fixture so I could mount the
workpiece on the mill spindle. I then mounted a round carbide insert on a
holder and put it in a lathe QC tool holder, just as I'd do for the lathe.
Then, I mounted the whole QC holder sideways in the mill's vise, facing
the right way for the mill's rotation. I wrote a simple arc program in the
X-Z plane to simulate the motion of the ball turning fixture. This produced
quite nice 1" diameter ball joint ends.

So, I think a tool with a round or radiused tip would give the best results.
If you have indexable carbide tools, pick the insert with the largest
radius.

If your lathe is not too rigid, or the ball turning fixture is a bit
loose, then
you will have to approach the workpiece in small increments, and not
take off
a lot of material per pass.

Jon