Now i know why i hated lathe castiron flywheels.... chips are damn hot and sharp.
1 roadrace car builder at Finland sayd, they wont lathe disc because there is hot/hardspots at disc, when at lathe, it will come little bit wave and wont work at racecars.
But when they grind it, hard/hot spots wont matter.

They are right. If you burn a flywheel it will harden the surface. Those spots are so hard it will push a cutter away. You get lumps.
Grinders don't care about those hard spots. The grinder will win that battle.