[GO-RIDE.com]

There's an easy way to keep the spur round while grinding off the teeth. Put a large bolt through the out-drive hole on the spur and then thread a nut on the bolt to tightly bind the spur to the bolt. (The bolt needs to be very close to the size of the out-drive hole.) Then put the bolt in an electric drill and set the drill to spin the opposite direction of the bench grinder. Start the bench grinder, get the drill spinning and slowly grind the teeth off with the drill spinning. This will give you a very close to perfectly round part in just a few seconds.