W. C. Houghton

The machine to be described in this article is intended to be of the simplest possible construction consistent with good workmanship and fair efficiency. It is of the bipolar type with a single field coil, and laminated armature. It might be easier to build it with a solid cast iron armature, but its output would be much smaller, while the power required to run it would be greater. Dynamos of such small size are at best rather inefficient because the field magnet must be made very strong or they will not generate.

This machine may be used either as a generator or as a motor. If used for the latter purpose, it will run a small lathe, several sewing machines or any similar machinery. The winding described will be what is known as shunt winding, i. e., the field will be connected in multiple with the armature. The effect of this is to make the machine run at practically constant speed as a motor, or to give a constant voltage as a dynamo. Series wound generators are used only for arc lights or for special purposes. They will not charge storage batteries nor run incandescent lights or motors satisfactorily. Series motors are only used where the speed must be varied between wide limits.

First, a few general remarks about methods of construction, and the order in which the various parts of the work should be taken up. All machine work should be completed first. Then the insulation of field and armature should be done, and lastly the winding. To do the machine work a good lathe is a necessity. An engine lathe is best, but a hand lathe with a good slide rest will do, if it will swing at least 9". A planer or shaper and a milling machine can also be used if available, but are not absolutely necessary. The field magnet casting should be taken up first. Plane or file off the feet on the base till it will stand perfectly true and firm. Drill a 1/4" hole in each foot, placing it well out toward the end so that screws may be put in easily. Next mark and centre punch the bosses on each side exactly in line with the centre of the cylindrical portion of the field, that is, the magnet core. Centre drill one of the bosses and drill a hole 1/2" deep in the other and tap a 3/8" No. 16 thread. These are for use in winding the field, which is done in the lathe.

The field may now be bored. This is best done by bolting to tool carriage of lathe, and using a boring bar with fly cutter. The ends of pole pieces may be faced off at the same operation by setting the cutter out and grinding it so it will cut on sides. If the tool carriage is not so built that the casting can be mounted on it, the next best way is to mount it on an angle-plate, which is then bolted to the large face plate of lathe. The work is then done with an ordinary boring tool. The boring need not be particularly smooth, but must be true, and of the same size from end to end, namely 1 7/8". Ends should be faced off to 2" length of bore. The next thing is to drill two i" holes through the pole pieces parallel with the armature shaft and 1 2/8" from the centre of it. To insure get-tiug these right, the best way is to make a jig, which will also be used in drilling the bearing yokes which must be spaced exactly the same. Take a piece of iron and turn it to fit the bore of the field magnet, and drill a J" hole through the centre of it. Next take a piece of flat bar steel say 1/4" x 3/4" and 3 1/2" long, scribe a centre line on flat side and drill three holes as per drawing of yokes. Drill two more holes between for rivets.

Put a piece of 1/4" steel through centre hole and through hole of round piece. Spot through and drill the two small holes, and rivet or screw the two together. The jig is then ready for use. Put the disc in field magnet bore, turn so that the centre line is parallel with the base, clamp in place and drill the holes through pole pieces. These are for the side rods that support the bearings. If a suitable count-erbore is available, both ends of these holes should be counterbored out, but this is not really necessary. This completes the work on the field magnet.

The bearing yokes should be filed fairly true on the back side of the end bosses, and then put in a 4-jaw chuck, two jaws holding on to the ends and the other two gripping the sides back of the central boss. The outer bosses may now be faced off, and the centre boss turned to 1/2" diameter, faced off and drilled and reamed to 1/4" for the bearing. The yoke is then turned over in chuck and the back of all three bosses faced off. Then take out of chuck, put on the jig with pin through centre holes and drill the side rod holes 1/4" diameter. Small oil holes may now be drilled and if desired, tapped for oil cups and the bearings are finished. The side rods are merely two 6" pieces of cold rolled steel 1/4" in diameter, threaded with a die, 1/2" on each end; thread 1/4" No. 20. The brass sleeves which serve as distance pieces will be described later.

The armature will now be taken up. First get some of the softest sheet iron, smooth and free of scale. Have a tinsmith cut from this enough 2" squares to make a pile 2" high when pressed together. Stack these up, hold them even with clamps, (wooden hand screws will do) and drill a 1/2" hole through the middle of them. Then clip off the corners with hand shears making them roughly octagonal. Now get two pieces of 1/8" soft steel, 2" square, drill and tap holes in the centre with standard 1/2" thread. The shaft is made of a 7" piece of 9-16" or 5/8" machinery steel which should be centered, turned down to 3/8 " for 2" on each end and the middle 1/2" diameter. Thread the 1/2" portion for about \" at each end with a die (standard) and screw on one of the 1/8" pieces of steel. Hold shaft upright in a vise and string on the armature discs, first shellacing them or else putting thin shellaced paper between them. Put on the other \" end piece, and screw up very tight, using a wrench and holding by the lower disc, not by the shaft.