In article , B.B.
says...

For class I'm turning an aluminum flywheel. 3" diameter. The steps
a face the sides, drill & ream the center, press onto a mandrel, turn
the outside and sides. Anyway, after pressing it onto the mandrel (yes,
I cleaned out the cutting oil) I've found that I have to go very slowly
or the cutting tool will grab the wheel and spin it on the mandrel.

Change the order in which you perform the operations.

1) clamp via the OD on the rough blank, and turn one side and the
part of the OD that is extending out from the chuck jaws, but leave
20 thou or so for cleanup later on the OD.

2) in the same setup, rough drill the bore.

3) Flip it around in the chuck, so that the jaws are now grabbing
on the finished OD from the previous step. Profile the second side
and the OD again to a 20 over size. Finish bore and ream the
ID dimension. (when you seat the part for this step, be sure
it is bottomed in the jaws and that there are no chips under
it)

4) use a stub mandrel in the headstock, with the stub turned
in place - at a diameter one thou under the bore size.
Also put a pusher block in the tailstock, a live center makes
this run easily.

Then your flywheel goes over the stub on the mandrel (which picks
up the finished bore) and the pusher block forces the part up against
the face of the mandrel, which now drives the part for taking the
final OD cut on the part.

You can glue some sandpaper on the mandrel face (which should be
only slightly smaller then the part's diameter) to assist with
driving it.

The benefit of this approach is:

The OD of the part is dead concentric with the bore, which is
the most important issue.

The OD is turned with the part held rigidly between two large
driver blocks - so there is much less chance for ringing or
chatter.

You can take as big a cut on the OD as you want because it
*will* drive.

How do I know all this? Because I spent a few years making
crane sheaves out of nylon. This is the way it was done, and
the OD cuts were often done with form tools, which require
large cutting forces and are very prone to chatter becaue of
the amount of tool engaged in the workpiece.

Make a stub mandrel and a pusher block, you could turn 20 flywheels
from blanks in a half hour.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================