It is not very difficult to make such a commutator. A hole is drilled through the fibre, which fits very tightly on the shaft. The shaft is then placed in a lathe with the fibre in position and the latter turned down until a piece of seven-sixteenths inch brass tubing can be driven on. The tube should be five-eighths of an inch long. Then mark two lines along the tube at points diametrically opposite. Bore two small holes to receive two small screws, a short distance away from each side of these lines and on each side of them. Make certain that the screws do not go into the fibre far enough to touch the shaft. The commutator may then be split along each side of the lines with a hacksaw, continuing the cut right through the brass and slightly into the insulating core. The heads of the screws should be filed off flush with the surface of the commutator and the latter trued up and made perfectly smooth. [Illustration: FIG. 126.—The Commutator.] If each section of the commutator is provided with a small brass machine screw near the back edge as shown in Figure 126, it will greatly facilitate connection with the ends of the armature windings. The armature, shaft and commutator, as they should appear when assembled are shown in Figure 127. Those portions of the armature and shaft which will come into contact with the armature wire should be insulated with shellaced paper. Soak the paper in the shellac until it is soft and it can be very easily pressed into proper shape to fit the armature. Allow the shellac to dry and harden before winding on the wire. [Illustration: FIG. 127.—The Armature and Commutator Assembled on the Shaft ready for winding.] The armature will not need to be fastened on the shaft if it is a tight fit and cannot be twisted. If it is loose, it may be fastened by means of a small set screw or pin. The commutator should fit the shaft very tightly so that it will not slip or twist. *The Armature Winding* is No. 20 B. & S. Gauge single-cotton covered magnet wire. Sufficient wire should be put on to fill up the winding space completely. Do not, however, put on too much wire or it will interfere with the field magnets and prevent the armature from revolving. Test the winding after it is finished to see that the wire is not "grounded" or connected to the armature at any point. If the insulation is perfect, give the winding a good coat of shellac and allow it to dry. The ends of the winding are each connected to one of the commutator sections as shown in Figure 127. *The Field Winding* is No. 20 B. & S. Gauge single cotton covered wire. The wire should be wound on in smooth, even layers, and the winding space between the flanges completely filled up. The winding space in the field frame should be insulated with shellaced paper by covering the core and the flanges. The flanges are best insulated with paper disks cut in two halves so that they will slip around the core. [Illustration: FIG. 128.—Details of the Wooden Base.]