a
true smooth bearing. Then trim about one-eighth inch off of the front
edge of the brush.

13. Q. Is it advisable to ever try to fit a brush with a file or knife?

A. Most emphatically no. You could not get a bearing across the brush no
matter how hard you might try with either a file or a knife.

14. Q. Why is it important to clean the scale off of the point of the
copper electrode each trip?

A. The scale on the copper electrode after it has cooled off is a
non-conductor of current, and acts as a blind gasket between the carbon
and the copper electrode. Unless this scale is removed, the current
cannot pass between the points of carbon and electrode and you cannot,
therefore, have a light. When the dynamo fields are compound wound, it
is unnecessary to clean scale from copper electrode oftener than once a
week, at which time copper electrode should be removed from holder and
all scale cleaned off. (With compound wound dynamo fields the cab lamps
will continue to burn when head-lamp is extinguished by lifting carbon
by hand.)

15. Q. How should the copper electrode be trimmed at the point?

A. The copper electrode should have about one-eighth inch surface on the
contact point.

16. Q. How far should the copper electrode project over the holder?

A. About one inch.

17. Q. Should the electrode be raised up to one and one-half inches,
what might happen?

A. If the copper electrode was run at a point so near the clutch, the
intense heat of the arc might do damage to the top carbon holder and
clutch.

18. Q. What regulation should be given to the tension spring No. 93 of
the lamp, and why?

A. This tension spring, No. 93, should be regulated when the current is
off the lamp and should be adjusted only tight enough to pull the magnet
yoke up against the top stop lug on the side of lamp column.

19. Q. If this tension spring was tightened too tightly, what might
happen?

A. At usual speed between stations, the movement of the engine would
impart an added resistance against the pull of the solenoid by the
tension spring, which would shorten up the arc and dim down the light.

20. Q. Is there anything else that could cause the light to dim down
when the engine is running fast?

A. Yes; if the spring No. 92-A that hold the heel of the clutch should
be too weak, the heel of the clutch would be forced up by the motion of
the locomotive; this would release the carbon which would fall to the
point of the coppe