To make a solid surface (such as metal, wood, or plastic) smooth by removing imperfections with the application of a strong and consistent frictional force, especially from a buffing wheel. Somebody scratched my car, so I'll have to take it to the shop to get it buffed down.
buff something down
to polish or smooth something by buffing. I buffed the newly waxed table down with a cloth. I'm going to go out and buff down the car.