** How to Make a Small Electric Motor [345] By W. A. Robertson

The field frame of the motor, Fig. 1, is composed of wrought sheet iron, which may be of any thickness so that, when several pieces are placed together, they will make a frame 3/4 in. thick.  It is necessary to layout a template of the frame as shown, making it 1/16 in. larger than the dimensions given, to allow for filing to shape after the parts are fastened together.  After the template is marked out, drill the four rivet holes, clamp the template, or pattern, to the sheet iron and mark carefully with a scriber.  The bore can be marked with a pair of dividers, set at 1/8 in.  This will mark a line for the center of the holes to be drilled with a 1/4-in. drill for removing the unnecessary metal.  The points formed by drilling the holes can be filed to the pattern size.  Be sure to mark and cut out a sufficient number of plates to make a frame 3/4 in. thick, or even 1/16 in. thicker, to allow for finishing.

After the plates are cut out and the rivet holes drilled, assemble and rivet them solidly, then bore it out to a diameter of 2-3/4 in. on a lathe.  If the thickness is sufficient, a slight finishing cut can be taken on the face.  Before removing the field from the lathe, mark off a space, 3-3/8 in. in diameter, for the field core with a sharp-pointed tool, and for the outside of the frame, 4-1/2 in. in diameter, by turning the lathe with the hand.  Then the field can be finished to these marks, which will make it uniform in size.  When the frame is finished so far, two holes, 3-3/8 in. between centers, are drilled and tapped with a 3/8-in. tap.  These holes are for the bearing studs.  Two holes are also drilled and tapped for 1/4-in. screws, which fasten the holding-down lugs or feet to the frame.  These lugs are made of a piece of 1/8-in. brass or iron, bent at right angles as shown.

The bearing studs are now made, as shown in Fig. 2, and turned into the threaded holes in the frame.  The bearing supports are made of two pieces of 1/8-in. brass, as shown in the left-hand sketch, Fig. 3, which are fitted on the studs in the frame.  A 5/8-in. hole is

[Illustration:  The Field-Coil Core is Built Up of Laminated Wrought Iron Riveted Together]

drilled in the center of each of these supports, into which a piece of 5/8-in. brass rod is inserted, soldered into place, and drilled to receive the armature shaft.  These bearings should be fitted and soldered in place after the armature is constructed.  The manner of doing this is to wrap a piece of paper on the outside of the finished armature ring and place it through the opening in the field, then slip the bearings on the ends of the shaft.  If the holes in the bearing support should be out of line, file them out to make the proper adjustment.  When the bearings are located, solder them to the supports, and build up the solder well.  Remove

[Illustration:  The Bearing Studs are Turned from Machine Steel Two of Each Length being Required]