Part 3 (1/2)

Now, before the pole piece (C) is put on, ill slip on a disc (E), made of hard rubber, then a thin rubber tube (F), and finally a rubber disc (G), so as to provide a positive insulation for the wire coil which is wound on the bobbin thus o further along in this work, you will learn the value, first, of winding one layer of insulated wire on the spool, coating it with shellac, and then putting on the next layer, and so on; when coht out at one end; but for our present purpose, and to render the explanation clearer, the wire terminals are at the opposite ends of the spool (H, H')

THE DYNAMO FIELDS--Two of these spools are so made and they are called the _fields_ of the dyna and 1/2 inch thick and 1-1/2 inches wide, then bore two holes through it so the distance measures 3 inches from center to center These holes are to be threaded for the 3/4-inch cores (A) This bar holds together the upper ends of the cores, as shown in Fig 23

[Illustration: _Fig 23_ BASE AND FIELDS assEMBLED]

We then prepare a base (J) of any hard wood, 2 inches thick, 8 inches long and 8 inches wide, and bore two 3/4-inch holes 3 inches apart on a middle line, to receive a pair of 3/4-inch cap screws (K), which pass upwardly through the holes in the base and screw into the pole pieces (C) A wooden bar (L), 1-1/2” 1-1/2”, 8 inches long, is placed under each pole piece, which is also provided with holes for the cap screws (K) The lower side of the base (J) should be countersunk, as at M, so the head of the nut will not project The fields of the dynamo are now secured in position to the base

[Illustration: _Fig 24_ DETAILS OF THE ARMATURE, CORE

_Fig 25_ DETAILS OF THE ARMATURE, BODY]

THE ARMATURE--A bar of iron (Fig 24), 1” 1” and 2-1/4 inches long, is next provided Through this bar (1) are then bored two 5/16-inch holes 1-3/4 inches apart, and on the opposite sides of this bar are two half-rounded plates of iron (3) (Fig 25)

ARMATURE WINDING--Each plate is 1/2 inch thick, 1-3/4 inches wide and 4 inches long, each plate having holes (4) to coincide with the holes (2) of the bar (1), so that when the two plates are applied to opposite sides of the bar, and riveted together, a cylindrical itudinally, and transversely at the ends; and in these channels the insulated wires are wound from end to end around the central block (1)

MOUNTING THE ARMATURE--It is now necessary to provide athis ar 26) is made, 2 inches in dia stem (6) of round brass, which projects out 2 inches, and the outer end is turned down, as at 7, to for 26_ JOURNALS _Fig 27_ COMMUTATOR, ARMATURE MOUNTINGS]

The other end of the armature has a si, turned down to 1/4-inch diameter up to within 1/4 inch of the disc (7), so as to for 27 is shown, at 10, a wooden cylinder, 1 inch long and 1-1/4 inches in diah axially, so that it will fit tightly on the stem (6) of the disc (5) On this wooden cylinder is driven a brass or copper tube (12), which has holes (13) opposite each other Screws are used to hold the tube to the wooden cylinder, and after they are properly secured together, the tube (12) is cut by a saw, as at 14, so as to form two independent tubular surfaces

[Illustration: _Fig 28_ END VIEW ARMATURE, MOUNTED]

These tubular sections are called the co 29_ TOP VIEW OF ARMATURE ON BASE]

In order to s are provided, each co 28), each 1/4 inch thick, 1/2 inch wide and 4-1/2 inches long Two holes, 3 inches apart, are forh this bar, to receive round-headed wood screws (16), these screws being 3 inches long, so they will pass through the wooden pieces (I) and enter the base (J) Midway between the ends, each bar (15) has an iron bearing block (17), 3/4” 1/2” and 1-1/2 inches high, the 1/4-inch hole for the journal (7) being28 shows the base, armature and commutator assembled in position, and to these parts have been added the commutator brushes The brush holder (18) is a horizontal bar made of hard rubber looselyAt each end is a right-angled metal arm (19) secured to the bar (18) by screws (20) To these ar ends engage with the co post (17), with the head thereof bearing against the brush-holder (18), serves as athe brushes with relation to the commutator

DYNAMO WINDINGS--There are several ways to wind the dynas 30, 31, 32, 33):

THE FIELD--If the field (A, Fig 30) is not a pernet, it must be excited by a cell or battery, and the wires (B, B') are connected up with a battery, while the wires (C, C') may be connected up to run a motor This would, therefore, be what is called a ”separately excited”

dynamo In this case the battery excites the field and the ar the lines of force at the pole pieces (E), so that the arathers the current for the wires (C, C')

[Illustration: _Fig 30_ FIELD WINDING]

[Illustration: _Fig 31_ SERIES-WOUND]

SERIES-WOUND FIELD--Fig 31 shows a ”series-wound” dynamo The wires of the fields (A) are connected up in series with the brushes of the armature (D), and the wires (G, G') are led out and connected up with a las 32 and 33, both the field and the ar andthe wires, the field is constantly excited by the current passing through the wires

SHUNT-WOUND FIELD--Fig 32 represents what is known as a ”shunt-wound”

dynamo Here the field wires (H, H) connect with the opposite brushes of the armature, and the wires (I, I') are also connected with the brushes, these tires being provided to perform the work required