The Diseases Of Electrical Machinery 1904
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ELECTRICAL MACHINERY,
3
ments, or to the commutator being out of truth or
having become slack ; while all the time the dynamo
attendant knows perfectly well the cause of the
trouble. In all such cases, therefore, it is advisable
carefully to turn down the commutator in order to
again obtain a perfectly smooth surface before com-
plaining to the builders of the machine.
The turning down of the commutator must be
done by a specially trained man, either between the
centres of an accurate screw-cutting lathe, or by
means of a special apparatus for turning down com-
mutators, such as has been designed by the author.
The purchase of such an apparatus is to be recom-
mended to all installation firms and engineers.
The following also comes under the heading of ruin
of commutators by careless handling. The workinj
surfqce of all properly designed commutators is longer
than the width of all the brushes on one spindle.
This is obviously in order that the brushes on one
spindle may be so staggered in relation to those on
the other spindle, that the surface of the commutator
is equally used and worn away. In many cases one
finds this rule not obeyed, and the brushes of all the
spindles exactly in line one with another. Thereby
parts of the commutator are not used, and in course
of time noticeable ridges appear. These cause the
brushes to lift on edge, so that they are lifted
partially from the commutator, thus causing sparking,
and in a short time destroying the commutator. In
B 2