A. The commutator.
10. Q. What care or attention should be given the commutator?
A. The commutator must be kept clean, free from dirt, and the mica must be kept filed a trifle below the surface of the copper bars.
11. 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.
12. Q. How are the brushes fitted?
A. Brushes are fitted by cutting a strip of No. 0 sandpaper about the width of the commutator surface (have the dynamo idle), place the strips of sandpaper under the brush, then pull the sandpaper from left to right; continue this process until the brush has been fitted to 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?