Ans. Considerable time is saved by the use of a machine designed for the purpose, such as shown in [fig. 387].
Fig. 386.—Another and simpler method of winding a "straight out" coil. A board with only two pins is employed as shown; this plan, however, gives more trouble in the subsequent opening out of the coil.
The construction of these machines is such that a roll of tape placed on a split metal ring is revolved around the coil to be taped, the coil being gradually moved until it is entirely covered.
Coil Retaining Devices.—In the operation of a dynamo there are two forces which tend to throw the inductors out of position:
1. Armature drag;
2. Centrifugal force.
Both of these forces are present with smooth core armatures, but only centrifugal force with slotted armatures. The devices used to hold the inductors in position against these forces are:
1. Driving horns;
2. Binding ribbons;
3. Retaining wedges.
Ques. What are driving horns?
Ans. They are simply pins or strips projecting from the surface of a smooth core as shown in [fig. 251].