Flip planer onto its top.

It's a good idea to clamp it to your stand or work surface before attempting to remove nut.

Place a piece of wood on the cutter assembly to lock it in place. The existing cylinder lock doesn't provide enough holding power.

Using both hands, gently work off the drive belt being careful not to pinch your fingers. Initially push down on the back side of the belt with your right hand while carefully twisting the pulley with your left. Once you get half way, move your right hand to the front of the pulley and press down. Take your time.

Using a 22mm socket wrench, holding it with both hands so you don't slip, and gently unscrew the drive nut. It only needs a short twist to break the torque then can be unscrewed the rest of the way by hand.

WARNING: The drive nut is a left-hand thread so you'll need to use the tightening setup on your wrench (turn clockwise).

Pull off the pulley.