Brad, who lurks in Benecia wrote (clip) Use a thin parting tool to go as
deep as you dare. Then stop the lathe, lock the spindle, and finish off
with the saw.
^^^^^^^^^^^
Brad, I thought of a better answer. In order to get as much use of the wood
as possible, use a Stewart tool, which is like a long parting tool, that is
usually used for bowl coring. Make a conical cut, starting farther up the
wood than both of us originally described, angled toward the bottom of the
platter. In that way you are making the sides of the platter blank higher,
without making the bowl smaller.