I made mine from a soup can I filled with molten aluminum, before I knew to not use so much extruded (pure) aluminum. That's part of the reason for the poor surface finish. That and not knowing nearly enough about bit geometry, feeds & speeds, etc.
Anyway, I chucked the whole chunk (after cutting off the can), faced the end, bored it for my grinder shaft size, turned down the large OD until it looked nice and seemed like a good size, then after marking out the area between what would become the flanges, I hogged away the material in the middle with a general turning bit. I got them down to the correct smaller OD, then used a parting bit to clean up the shoulders, then parted off the outer one, faced the second one to length, then parted it off as well. No centers or complicated workholding needed.