A. In using emery paper a piece of emery might lodge in the grooves between the commutator segments, and being a conductor of electricity, causes short.  Will also get embedded in the copper and cut the brushes.  Sand will not do this.

35.  Q. State how you would go about to focus a lamp?

A. (1) Would adjust back of reflector so front edge of reflector would be parallel with front edge of case. (2) Adjust lamp to have point of copper electrode as near the center of reflector as possible with carbons as near the center of chimney hole as you can set them. (3) Have the locomotive on straight track.  Now move the base of the lamp around until you get a parallel beam of white light straight down the center of the track, then tighten lamp down.

36.  Q. If the light throws shadows upon the track, is it properly focused?

A. No.

37.  Q. If the light is properly focused, that is, if the rays are leaving the reflector in parallel lines, but the light does not strike the center of the track, what should be done?

A. When the light rays are thrown out in parallel lines and they do not strike the center of the track, it denotes that the headlight case is not set straight with the engine, and the entire case on baseboard must be shifted until the shaft of light strikes the track as desired.

38.  Q. What can you do to insure a good and unfailing light for the entire trip?

A. By carefully inspecting the entire equipment before departing on each trip and know that there are no wires with insulation chafed or worn off; that all screws and connections are tight; commutator clean; brushes set in brush holder in the proper manner; carbon in lamp of sufficient length to complete trip; copper electrode cleaned off and oil in both bearings.

39.  Q. Why would you not fill the main oil cellar full of oil?

A. If you should fill the main oil cellar full of oil, the oil would run out of the overflow holes on the side and all over the equipment and locomotive and could do the dynamo no good but possibly harm.

40.  Q. What is the most vital part of the dynamo?

A. The commutator.

41.  Q. What care and attention should be given the commutator?

A. The commutator must be kept clean, free from dirt and grease; the mica must be kept filed down about one-sixty-fourth of an inch below the surface of the bars.

42.  Q. How should you clean the commutator, and when?

A. The commutator should be cleaned before starting out on each trip by using a piece of damp waste, rubbing the bars lengthwise, then wipe dry with clean dry piece of waste.

43.  Q. What kind of a bearing should the brush have on the commutator?

A. Brushes should be fitted to have a bearing with the same contour as the commutator, with bearing covering no less than two of the commutator bars, nor more than three of the bars.