How many times can a flywheel be re surfaced?

When I was young and stupid, we had a disk lathe and somewhere I'd read (the destructions) about turning a flywheel. What a disaster. HARD SPOTS. Pretty soon the thing looked like a stone/ concrete sidewalk. Big "welts" sticking up were the hard spots, with low spots where the tool and "sprung" down and cut deeper. had to find someone with a surface grinder That was around 1975, I don't remember the details