DIY Flywheel / PP / Rotor / Drum Balance Checking Fixture

How do you center the arbor, IE stuff like rotor/ disc lathes use cones to center in a bore. You want the fit precision enough that runout in the arbor to device under test does not itself cause off-center and therefore imbalance

Seems like a great idea. No, how would you compare say, a weighted 360 flywheel to something you are trying to duplicate? Like a balanced wheel to a weighted wheel?

Interesting project