[Tom Wesenberg]

I don't ever recall hearing of brushes binding on the commutator, but I use an ATLAS hobby saw from the Model Rail Road store to undercut the insulation between the commutator bars to about .010". After the undercut is done I spin the armature in my lathe while holding fine crocus cloth against the commutator. I spin it both directions, and this will remove any sharp edge from the bars, and in fact it will give the edge a slightly rounded surface for the brushes to enter each bar. A sharp edge could wear the new brushes very quickly.

Also notice the brushes have a slight angle where they contact the commutator. This angle gives each brush a short side, and a slightly longer side. The shorter side always faces the pivot post for that brush. Also note the thin brush is the adjustable brush.