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.

Any advice appreciated.

Thanks,
Chris

"Chris" wrote in message
oups.com...
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.

Any advice appreciated.

Thanks,
Chris

Excessive front clearance and rake are an open invitation to hogging and
chatter. Reduce the amount of each and you should have pretty good luck,
assuming the tool is otherwise ground properly. If you're machining steel,
there's no need for more than about 7° front clearance, but rake can be
included as your chip breaker so it's open to wide variations. A straight
grind rake of roughly 10° should serve you nicely. You'd be best served if
you make the tool cut in one direction, so the rake is in keeping with the
direction of feed, sort of a combination of side and back rake. If you
don't want to do that, make sure it's straight back so it doesn't go
negative on you in one direction, especially if you're using HSS.

Harold

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

Thanks for the tips. I adjusted the attachment a bit and tried some
different tool shapes today and got somewhat better results. I think
with some practice and grinding some new profiles I might get there
eventually!

Chris