Ques. How should low commutator segments be treated?
Ans. The commutator surface may be turned down to the level of the low segment, or the latter may be pulled out again to its former level, this latter being the preferable method, if it can possibly be effected.
Ques. How is a commutator segment pulled out to its correct position?
Ans. A hand vise is firmly clamped to the lug, or a loop of copper wire is passed round the conductor where it joins the commutator. A bar of iron, to act as a lever, is supported on a fulcrum over the commutator, and one end of the bar is passed through the loop or vise. Pressure is applied to the other end which will generally bury the segment up to its proper position.
How to Re-turn a Commutator.--In re-turning the commutator, the armature should first be carefully taken out of the armature chamber, avoiding knocks or blows of any kind. The whole of the winding should then be wrapped in calico or canvas before the armature is put into the lathe, to prevent any particles of metal becoming attached to the surface of the armature at the time the commutator is being turned. The armature should on no account be rolled upon the floor, or subjected to blows or knocks while being put into the lathe.
In re-turning the commutator, a sharp pointed tool should be used with a very fine feed. A broad nosed tool ought not to be used, as it is liable to burr over the segments. After turning, the commutator should be lightly filed with a dead smooth file, and finally polished with coarse and fine sandpaper. After the commutator has been turned and polished, the insulation between the segments should be lightly scraped with the tang of a small file to remove any particles of metal or burrs which might short circuit the commutator.
The points where the armature wires are soldered to the lugs should also be carefully cleaned with a brush, and should then receive a coat or two of shellac varnish.
While the commutator is being turned, care should be taken that the setting marks for the adjustment of the brushes are not turned out if these be present. The same care should be used in putting the armature back into the armature chamber as was used in taking it out, otherwise the insulation may be damaged.
Figs. 719 and 720.--Bissell commutators. The segments are of hard drawn copper and are insulated from each other and from the shell by mica.
Ques. Should the commutator be run without any lubricant?
Ans. In most cases it will be found that a little lubricant is needed in order to prevent cutting the brushes, cutting the commutator; this is especially the case when hard strip brushes are used. The quantity of oil applied should be very small; a few drops smeared upon a piece of clean rag, and applied to the commutator while running, being quite sufficient.