Removing brushed on RUST-OLEUM from axle housing?

mycuda said
Still need to finish sand to at least 220 grit before prime or paint.
Otherwise wasting your time

I have used flap discs for years, great tool. LIke he said, with 80 grit , even 120 it will leave bad scratches on sheetmetal, probably on that rear end metal too. Pointing this out since you are going to all this trouble. Give 'er hell