On Dec 27, 12:29*pm, Chris Wilson wrote:
I need to machine a round billet of stainless steel on its flat face with a
square section groove to take an O ring. The OD needs to be about 60 mm,
the ID 50 mm and the depth of the groove 4 mm. I have a smallish (11 inch
swing Harrison) lathe....

If you aren't comfortable cutting straight in with a square tool you
could grind a triangular bit like a threading tool but about 20 to 30
degrees between sides and cut in a little at a time with it. Angle the
tool so only the tip cuts, run in with the carriage until it starts to
complain, back off a little and cut in or out almost to the other
wall. Once you have roughed out most of the groove you can use a
square-ended bit narrower than the slot so only one side cuts at a
time.

The pointed tool I use is rounded on the end and nearly flat on top so
it cuts in both directions. The angle is ~30 degrees. I use it to
rough out belt grooves on mandrel-mounted pulleys, which won't stand
much cutting force.

jsw