If you have a LOT of pots and pans to recondition-- as you might if you were running a thrift shop-- then a machine grinder from the auto shop can be a very handy tool. (So can a sanding pad on a drill.) But for the home reconditioner, salt is a very good abrasive and it takes time to use, so that one gets to mull over all one's indiscretions and pot-misuses, or one's happy memories of the meals a relative produced out of the poor old pot... or the actual extent of the need to have clean-looking pots at all.