Thanks for the explanation. I have a lathe, and expect I will be able to do most of the work on it by adjusting the centers and scroll chuck. I also have a Longworth chuck, if I decide I can shape a more or less square perimeter for the board.
Your router bit is called a core box bit.
I've been chopping nuts on a flat chopping board with a French chef's knife, and a hand spread out over top of the work. It stops a lot of the nut fragments, and the dogs get the rest.