Smoke from Motor - Drills

If oil got on the brushes, this can happen, and it will clear. It can also happen when windings have shorted out from being run too hot with subsequent failure of varnish. The brushes will tend to arc and the commutator contact bars begin to erode and melt. The motor may continue to run albeit slowly and without power.

Also too, sometimes the speed control circuit flames out and appears as smoke from the motor. in which case the motor becomes nonfunctional.

The same can happen when wires get shorted out.