The small fittings can be made now while the windings are drying. An easily made commutator for this dynamo is shown on the drawing. The foundation for it is a brass tube 5/8 in. in diameter and 21/8 in. long, bored for a driving fit on the shaft. On one end should be sweated (soldered) a brass washer 1/8 in. thick and 1 in. in diameter, while the other end should be tapped and fitted with a nut 1/4 in. thick. The insulation of the commutator is of fiber. Take a piece of fiber and turn it into a piece 11/4 in. diameter, 15/8- in. long and bored to fit over the tube. In the center turn a groove 1/8 in. deep and in. wide. Cut the sides of the groove in at an angle, as shown in the drawing.

Next cut the fiber in two about in the middle of the groove. Take a piece of copper tube with inside diameter sufficient to slip over the grooved part of the fiber and a wall at least 1/8 in. thick. Set this on an arbor and turn the ends at an angle in the fiber making the outside just 1 in. long. The inside will be longer so as to fit under the fiber. Cut the copper tube into six equal parts lengthwise, clean the saw marks and burrs off carefully with a fine file and set the parts between the fiber pieces.

To fill the space between the segments, cut pieces of fiber the shape of the cross section of the copper. Now set the parts together and drill, and tap each of the segments close to one end for a 1/4 in. 4-32 machine screw. Set the commutator in the lathe and carefully turn the surface down true, but do not take off any more material than necessary. In case the dynamo is is being wound and used for a high voltage I would suggest the spaces between segments be filled with a paste made of powdered mica and shellac which, when dry, is very hard, durable and a good insulator. It will be necessary to also fill the space between the fiber pieces with this paste. Possibly the commutator may have to be wrapped with paper to hold the paste in until it dries.

The brush poke can be castor cut out of 1/2 in. brass-stock. The dimensions are given on the drawing and can be followed, or the builder can design one which might better suit his fancy. The center hole should be carefully drilled to a running fit on the bearing pedestal. Any type of clamping screw may be used that would draw the sawcut together. A simple and easily made brush holder and rigging is shown in the drawing. The brush holder stud is insulated from the yoke with a fiber bushing and washer, as shown. It has a sawcut at the other end wide enough to admit the brush holder and spring. A machine screw should be fitted at the end to bring the two halves together, clamping the holder in place. The brush holder is of sheet brass, bent into the shape shown. The spring is made of spring brass. The brush is of woven wire 1/4*1/2 in. and about 8/8 in. long. It should be carefully fitted to the commutator in order to give a good current carrying contact.

The commutator should be assembled on the shaft and connected up to the winding. The loops connected to the next segment beyond the one opposite the coil from which the loop comes. This will bring the brushes in a position which will require the yoke in a horizontal position. Set the brush yoke in position and assemble the armature in place, turning it with the hand to see that it runs freely, then assemble the brushes and adjust the spring.

To drive the dynamo use a pulley 21/2 in. in diameter with 18/4 in. or 2 in. face and use a 1 1/2 in. flat belt. Connect the field coils in series so that the current will traverse them in the same direction. Connect the outsidewires from the field, one wire to one brush stud and the other to the other brush stud. One of these studs will be the positive and the other the negative terminal of the dynamo.

The machine is now ready to run, but inasmuch as no current has passed through the fields, it is quite probable that it will not generate. It would be well, threfore, to connect the fields to one or two cells of battery in order to get sufficient residual magnetism with which to start the dynamo. If everything is connected up correctly the machine should now generate current. Should it fail to do so try reversing the field leads, or test for an open circuit. As the dynamo will run as a motor a good way to test it is connect it to a battery of 10 or 12 cells, and if every-tGing is right it will run, and turn in the direction in which it should be driven as a dynamo; the only difference being in the position of the brushes. As a generator the brushes will have a lead; that is it will be ahead of the neutral line of the armature, in the direction of rotation, while as a motor the brushes will lag.

The finish of the dynamo can be made to suit the builders' fancy, a dark green or dark brown enamel or bicycle paint would look very good. The material for this dynamo would cost between $7 and $10, depending upon the facilities the builder has and the proximity to source of supplies. When complete the dynamo should easily be worth $20.

The amount of wire required will be approximately 4 1/2 pounds of either No. 20 or No. 22 for the fields and about 1 1/4 in. pounds of No. 16 for the armature. To generate 55 volts, wind the armature with No. 20 wire 60 turns per coil. This would require 1 1/4 pounds of wire. Wind the field with No. 26 wire, 2930 turns per pole. This winding will take 1/4 ampere of field current. As a generator with the above winding will give a current of 3 amperes.