don't be afraid to cut the fins off with a hacksaw. it's more work than doing it on a lathe but the results are the same if you work carefully. after i file off the rough cuts i sand it down on a large belt sander table in my carpentry shop and constantly check the thickness at different points around the circumference.

in the pic is an echo flywheel that i sanded by hand with sandpaper glued to a marble slab before i remembered about the belt sander in my shop :stupid:

dave