The machine will be divided into three main parts, the construction of each of which will be taken up in turn and the method of procedure discussed in detail. These parts are the completed armature, the field and bearings, and the brushes together with suitable terminals and connections.
The armature core is constructed from a number of pieces, having dimensions that correspond to those given in A, Fig. 1. These pieces are cut from thin annealed sheet iron, in sufficient number to make a pile, 3/4 in. high, when placed on top of each other and firmly clamped. It would, no doubt, be best to first lay out one of these pieces very carefully and then cut it out and mark out the other pieces with the first one as a pattern, being careful to file off all the rough edges on each piece.
Details of the Armature Laminations and the Commutator Segments, and the Method of Mounting Armature Core and Commutator (Fig. 1)
Now obtain a piece of 1/4-in. iron or brass rod, 3-1/4 in. long, that is to serve as a shaft upon which to mount the armature and commutator. This rod is threaded for a distance of 7/8 in. on one end and 1-7/8 in. on the other. Procure five brass nuts, 1/8 in. thickness, to fit the threads on the rod. If possible have the ends of the rod centered before the threads are cut, for reasons to be given later. Place one of the nuts on that end of the shaft that is threaded for 7/8 in., and in such a position that its inner surface is 3/4 in. from the end of the rod. Solder this nut to the rod when it is in the proper place and remove all extra solder. Drill a 1/4-in. hole in each of the armature stampings and place them on the shaft, clamping them together with three small clamps, one on each extension or pole. Then place a second nut on the shaft and draw it up tight against the last stamping placed in position, and solder it to the shaft. Next wind two or three layers of good strong tape around each of the rectangular portions of the armature and then remove the clamps. Make sure that all the edges of the different laminations are perfectly even before applying the tape.
The shaft is then placed between two centers to determine whether the core is approximately balanced and runs true. If the armature core is unbalanced or not true, the trouble should be corrected before proceeding with the remainder of the armature construction. The armature winding is not to be put on the core until the commutator has been constructed and mounted on the shaft.
The commutator consists of three pieces of thin sheet brass similar to that shown at B, Fig. 1, mounted on the surface of a cylinder of insulating material, 3/8 in. long and 7/8 in. in diameter. A 1/4-in. hole is drilled lengthwise through the cylinder of insulating material. Bend the pieces of brass around the outside of the cylinder, and turn all the lugs, except the center one, marked C, over at right angles and put a small nail or screw through the holes in the ends of the lugs into the cylinder. These pieces of brass are equally spaced around the cylinder so that all the lugs, not turned down, project in the same direction. Now place a nut on the end of the shaft that extends the greatest distance through the armature, so that its outside surface is 1/2 in. from the surface of the end of the armature core next to it, and solder the nut to the shaft. Place the commutator on the shaft so that the projections on the pieces of brass are toward the armature core and the spaces between the ends of the pieces occupy the position relative to the cores, shown at A, Fig. 2. Another nut is then placed on the shaft and drawn up tight against the cylinder. The proper spacing of the various parts on the shaft of the machine is shown at D, Fig. 1. Another small nut is placed on the end of the shaft, away from the commutator, so that its outside surface is 1/2 in. from the surface of the end of the armature core.
Diagram of the Winding on the Armature and Detail of the Field Laminations (Fig. 2)
The threads on that part of the shaft extending beyond the last nut on each end are now filed off, which can be easily done by placing the shaft between the centers of a lathe and revolving it quite rapidly, the file being applied to the parts that are to be cut down.