Metal prep before welding: which grinder discs do what

Cutoff wheels (.045") cut. Grinding wheels (1/4") remove a lot of metal fast, leave deep scratches. Flap discs (40 to 80 grit) blend welds and clean mill scale; this is the one you will use most. Wire wheels strip paint and rust without removing metal, and they throw wires at your face. Strip discs (the purple ones) remove paint and scale without scratching.

Keep the guard on. Flap discs do not explode; grinding wheels and cutoff wheels do. Two grinders, one with a flap disc and one with a cutoff, saves endless swapping.