Armature.  The iron upon which the armature conductors are wound is called the core.  The core of an ordinary armature is shown in Fig. 69.  This is usually made of soft gray cast iron, turned so as to form bearing surfaces at 1 and 2, upon which the entire armature may rotate, and also turned so that the surfaces 3 will be truly cylindrical with respect to the axis through the center of the shaft.  The armature conductors are put on by winding the space between the two parallel faces 4 as full of insulated wire as space will admit.  One end of the armature winding is soldered to the pin 5 and, therefore, makes contact with the frame of the generator, while the other end of the winding is soldered to the pin 6, which engages the stud 7, carried in an insulating bushing in a longitudinal hole in the end of the armature shaft.  It is thus seen that the frame of the machine will form one terminal of the armature winding, while the insulated stud 7 will form the other terminal.

[Illustration:  Fig. 69.  Generator Armature]

Another form of armature largely employed in recent magneto generators is illustrated in Fig. 70.  In this the shaft on which the armature revolves does not form an integral part of the armature core but consists of two cylindrical studs 2 and 3 projecting from the centers of disks 4 and 5, which are screwed to the ends of the core 1.  This =H= type of armature core, as it is called, while containing somewhat more parts than the simpler type shown in Fig. 69, possesses distinct advantages in the matter of winding.  By virtue of its simpler form of winding space, it is easier to insulate and easier to wind, and furthermore, since the shaft does not run through the winding space, it is capable of holding a considerably greater number of turns of wire.  The ends of the armature winding are connected, one directly to the frame and the other to an insulated pin, as is shown in the illustration.

[Illustration:  Fig. 70.  Generator Armature]

[Illustration:  Fig. 71.  Generator Field and Armature]

The method commonly employed of associating the pole pieces with each other and with the permanent magnets is shown in Fig. 71.  It is very important that the space in which the armature revolves shall be truly cylindrical, and that the bearings for the armature shall be so aligned as to make the axis of rotation of the armature coincide with the axis of the cylindrical surface of the pole pieces.  A rigid structure is, therefore, required and this is frequently secured, as shown in Fig. 71, by joining the two pole pieces 1 and 2 together by means of heavy brass rods 3 and 4, the rods being shouldered and their reduced ends passed through holes in flanges extending from the pole pieces, and riveted.  The bearing plates in which the armature is journaled are then secured to the ends of these pole pieces, as will be shown in subsequent illustrations.  This assures proper rigidity between the pole pieces and also between the pole pieces and the armature bearings.