circular motion, rolling around. A grinder would have taken more high surface all over, VERY hard to get the even edge on grinder, I'm used to one, don't think I could duplicate. Now, that said, could have been a belt sander but most likely a flat fan belt, but still, more high points would have been affected.
Dryer or similar rotating machine, belt fed coin machine is my #1 pick

Dryer or similar rotating machine, belt fed coin machine is my #1 pick
























