The assembler places the outer rim on the rotating table as a propane torch heats up the empty rim. The hot rim is placed on a solid block leveled table over the back space plates. The center is then carefully lowered into the hot rim to sit on the back space plates, the outer is allowed to cool and shrink onto the center. It is then aligned to within + or - .020 run-out. Once aligned it goes to weld where the mig-welder gun is aligned for the best fillet bead where the center meets the outer. Checked for truesness after welding, detailed, boxed and ready for you.