The Diseases Of Electrical Machinery

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