Martindale, BRSRX27-MH, 8" x 1-1/2" x 1-1/2" Brush Seating and Cleaning Stone, Medium Hard
Similar to grade MS except harder. It was specifically developed for use on undercut commutators where softer grades might wear too quickly.
Commutators and slip ring brushes of any material can be easily and accurately seated with Diamond D Brush Seaters. Just hold the Brush Seater on the commutator close to the brush so the Brush Seater material will be carried under the brush. At the same time, press on the brush to increase pressure. Many commutators and slip-ring troubles are caused by poor contact with the brushes. This is particularly true when new brushes are installed along with old ones because if the new brushes do not make good contact, the current is forced through the other brushes. This overloads the other brushes causing pitting of the brush faces, loosening of brush shunts, burning of brush holders, and many other evils that result from sparking and heating.
