I have some old Otis adjusting manuals that say to set neutral with 2 "test brushes" or make your own by filing brushes to a point exactly on the centerline of the brush so they only contact one bar each. After setting the brush angle and quartering of course. Never gone that far myself but it is something to think about. I use 6vdc batteries and a 50mv analog DC meter in a little apparatus I made for setting neutral.
