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152 RICHARDSON'S BLUEBOOK OF PROJECTION
Sandpapering
(76) In the event it becomes necessary for any reason, to clean the commutator surface right down to the copper, use No. 00 sandpaper. Do not use anything coarser than No. 00 and under no circumstances use emery paper or emery cloth. Remove all brushes and, having started the motor (we are still considering motorgenerators), hold the sandpaper against the commutator, without exerting too much pressure, until the copper shows clean and bright allover the surface.
(77) Stop the motor and give the commutator a vigorous brushing endwise. Next whittle a hardwood stick until its point will just fit into the undercut between commutator bars. Draw this through each one of the undercut slots to dislodge any copper bits that may have been drawn either across from one bar to another or down into the groove. Then brush endwise again vigorously.
(78) There are "commutator stones" on the market, which are rectangular bricks of fineness or coarseness to suit any "dressing" job.
The stone is held against the rotating commutator, and its surface wears down readily to fit the commutator curvature, in the meantime cutting freely. Unless the brushes are raised, they too will partake in this rapid wear-away-spree. In fact one way of fitting the brush ends to the commutator curvature is to let them rest in their natural position on the commutator and operate with a rather fine grade of commutator stone. The fit thus secured is perfect.
(79) After the stoning is finished, brush vigorously endwise to remove all grit and bits of copper from between the bars. Next, hold against the rotating commutator the lubricating pad which we shall presently tell you how to make. Then adjust the brushes and the commutator "dressing" is done.
Commutator Lubricating Pad
(80) To make this pad proceed as follows: From a