These tubular sections are called the commutator plates.
In order to mount this armature, two bearings are provided, each comprising a bar of brass (15, Fig. [28]), each ¼ inch thick, ½ inch wide and 4½ inches long. Two holes, 3 inches apart, are formed through this bar, to receive round-headed wood screws (16), these screws being 3 inches long, so they will pass through the wooden pieces[p. 46] (I) and enter the base (J). Midway between the ends, each bar (15) has an iron bearing block (17), ¾" × ½" and 1½ inches high, the ¼-inch hole for the journal (7) being midway between its ends.
Commutator Brushes.—Fig. [28] shows the base, armature and commutator assembled in position, and to these parts have been added the commutator brushes. The brush holder (18) is a horizontal bar made of hard rubber loosely mounted upon the journal pin (7), which is 2½ inches long. At each end is a right-angled metal arm (19) secured to the bar (18) by screws (20). To these arms the brushes (21) are attached, so that their spring ends engage with the commutator (12). An adjusting screw (22) in the bearing post (17), with the head thereof bearing against the brush-holder (18), serves as a means for revolubly adjusting the brushes with relation to the commutator.
Dynamo Windings.—There are several ways to wind the dynamos. These can be shown better by the following diagrams (Figs. [30], [31], [32], [33]):
The Field.—If the field (A, Fig. [30]) is not a permanent magnet, it must be excited by a cell or battery, and the wires (B, B') are connected up with a battery, while the wires (C, C') may be connected up to run a motor. This would, therefore, be what is called a "separately excited" dynamo.[p. 47] In this case the battery excites the field and the armature (D), cutting the lines of force at the pole pieces (E), so that the armature gathers the current for the wires (C, C').
Series-wound Field.—Fig. [31] shows a "series-wound" dynamo. The wires of the fields (A) are connected up in series with the brushes of the armature (D), and the wires (G, G') are led out and connected up with a lamp, motor or other mechanism. In this case, as well as in Figs. [32] and [33], both the field and the armature are made of soft gray iron. With this winding and means of connecting the wires, the field is constantly excited by the current passing through the wires.