Greg,
I have read of this techinique before but never tried it. Here is someone else's description of making smaller spheres. It ain't turning but may be of interest.
"Faced with having to reproduce a number of 1/2-inch diameter
wooden balls (to replace missing ornamentation on an old
fireplace), I discovered a virtually painless procedure using a
large belt sander. Build a box frame, open on the bottom, and
clamp it to the stationary part of the sander so it sits just off the
belt. For 1/2-inch diameter balls, cut 1/2-inch cubes and toss them in
the box frame. Put a cover on the box (Plexiglass is best) and turn on
the sander. The sanding belt will throw the cubes around in the frame
like dice on a game table, knocking off their corners and edges until
they are perfect spheres."