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MANAGERS AND PROJECTIONISTS 503
it off on the face of the pad, the idea being to get the oil evenly distributed on the pad.
Remember this, however, too little lubrication is better than too much, and heavy lubricants (thick oils) must never, never, never be used on a commutator. If one application, as above, during every six-hour run does not suffice, then it is likely that (1) brushes have too much tension, (2) machine is overloaded, (3) brushes not properly set, or (4) someone has put in the wrong kind of brush, which of course is not likely to happen if the machine be a new one just from the factory, but is quite possible if it be a second-hand machine, or one which has been in a repair shop.
Never use gasoline or benzine around a commutator; it is likely to attack and soften the shellac and insulation, and thus set up serious trouble.
CAUTION. — Where the mica insulation of the commutator is undercut, great care should be taken with regard to lubricating of the commutator. If a soft brush is used no lubrication at all should be applied. This last caution is necessary with undercut insulation, because the lubricating medium will have a tendency to combine with carbon dust and fill up the space between the commutator bars, thus in time possibly short circuiting the bars; also where soft brushes are used the brushes themselves, as a rule, contain sufficient paraffine to provide all necessary lubrication.
(d) See to it that sufficient oil, or combined oil and carbon dust, does not collect at any point or spot, either on the commutator or the face of any brush, to form a semiinsulation.
(e) That there are no high or low bars, and that the commutator is perfectly round.
(f) That a fragment of copper does not drag across the insulation between two adjacent bars, or that oil and carbon dust do not form such a bridge. This fault will be evidenced by a thin, sparkling ring of light around the commutator.
(g) That the brush springs do not carry sufficient current to heat them.
(h) That the brushes fit properly in their holders, and are kept free from accumulation of dirt, dust, etc. They should be taken out, their faces examined, and if necessary cleaned at the end of every 60 hours' run.
(i) That the brushes are neither too hard nor too soft.
(j) That the armature of horizontal type machines "floats"