Are all the bars uniform in appearance, If not then the armature is gone.
Use 400 grit silicon carbide paper, brighten them up a bit if you are worried. You really do not want to move any metal, The old time turn in a lathe is not terribly useful as modern motors run very high RPM. I used a collet lathe, nothing else was accurate enough. They tend to rough turn, knurl and heat treat the shaft, then center-less grind so the center holes in the end of the shaft are not always on center. You can polish by hand, anything more takes good tools. Almost all brushes come from China now, and the quality can vary very widely. You want to watch the brushes closely and replace when worn so you do not damage a very thin commutator by arcing. Be sure to clean to undercutting between the commutator bars.
Rod