"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