the shoulder as shown in Fig. 35. As the diameter of the piece grows smaller, lighter cuts must be taken to prevent undue springing of the shaft. 35 FIG. 35.-First Operation in Turning Armature Shaft. The second operation consists in reducing the end of the shaft to a diameter of inch from the end to the shoulder where the thread begins, as shown in Fig. 36. 36 FIG. 36.-Second Operation in Turning Armature Shaft. The third operation is to thread the shaft for a distance of about 3 inch from the shoulder, as shown in Fig. 37. If this operation is done in an engine lathe, the steady 37 FIG. 37.-Third Operation in Turning Armature Shaft. rest should be set at about the center of length of the shaft while the thread is being cut. The piece of work can now be reversed between the 38 FIG. 38.-Fourth Operation in Turning Armature Shaft. lathe centers and the opposite end of the shaft operated on as shown in Fig. 38, which consists of reducing this end of the shaft to a diameter of 5/16 inch from the end of the shaft to the collar. The fifth operation consists of reducing the same end 39 FIG. 39.-Fifth Operation in Turning Armature Shaft. of the shaft to 3/16 inch for a length sufficient to accommodate the bearing and pulley as shown in Fig. 39. The sixth and last operation is to reverse the shaft in the lathe and turn down the opposite end to a diameter 40 FIG. 40. Sixth Operation in Turning Armature Shaft. of 3/16 inch to fit the bearing as shown in Fig. 40. The portions of the armature shaft which are to revolve in the bearings must be turned very true and should be finished. with a "dead smooth" file. CHAPTER X ARMATURE As soon as the shaft is completed the armature can be assembled as the punchings are supplied in a finished state. These are of electric steel which possesses great magnetic permeability. These punchings, as shown in detail in Fig. 41, contain eight circular slots for wire. With each set of punchings is furnished two punch FIG. 41. Detail of Punchings for Armature. ings of the same shape made of hard fiber which are to be placed, one at either end of the armature. Their function is to prevent the insulation of the wire of the coils from being cut and a short circuit, or "ground," being formed in consequence, as would be the case if a metal punching were used on the end of the armature instead. Fig. 42 shows the method of building up the armature. One of the fiber punchings is first placed on the armature shaft and pushed up against the collar on the shaft, and this is followed by the iron punchings. To keep the punchings in position as they are placed on the shaft, a piece of metal the same diameter as the circular slots of the armature should be placed in the position shown in Fig. 42. This will keep the slots in line until the required number of punchings have been placed on the shaft. OC FIG. 42.-Building up Armature. The number of punchings required are sufficient to build up an armature two inches in length. When the required quantity are on the shaft the second fiber punching is placed in position on the outer end and this is followed by the 5/16-inch brass nuts. The punchings should be carefully squeezed together in the vise, turning the armature around so as to press each portion down equally. The piece of metal rod placed in the slot of the punchings should not be removed until after the nut has been tightened down to clamp the punchings securely together. After the punchings are secured the armature should be placed in the lathe and, with a hand turning tool, the greater portion of the brass nut should be cut away as well as all the thread on the armature shaft, which protrudes beyond the brass nut. This is shown in Fig. 43, where the original size and shape of the nut is shown ARMATURE FIG. 43.-How to Remove Sharp Corners of Clamping Nut. in dotted line, and the solid lines indicate the shape of the nut after cutting down. The reason for cutting away the nut is to make more room for the armature wire and also because the original FIG. 44.-Armature Assembled Ready for Winding. sharp corners of the nut are liable to cut the insulation of the wire when the armature is being wound. The circular slots of the armature should next be cleaned of all burrs and projections. This can best be |
