Fig. YI shows brush holder yoke (16) which is 5Va inches between
centers of brush holders ; 3 inches in diameter in the center, bored out 2 inches
to fit collar ; holes in ends l /z inch to receive insulating bushings (23) . The
handle (34) can be made of hard wood. 22 is an insulating washer 1 inch in
diameter ; 23 is the insulating bushing. Their positions are shown in Fig. III.
19 is the brush holder with brush (26) in position. The holder is slotted out to
the proper width of a brush. Plate 25 is placed over the brush (26), and
screws (24) going through plate (25) into brush holder (19) hold the brush
firmly and at the same time admit of easy adjustment of the brushes. The
brushes are made of several layers of thin spring sheet copper. They are 4
inches long; 1 inch wide and 3 /ic inch thick. The object of using several
layers is to get sufficient surface on the commutator and still have the brush
PRACTICAL DYNAMO BUILDING. 35
Fig. VII shows the commutator in detail. 11 is the end view ; 15 are
the screws for fastening the lead wires to the segments ; 13 the brass heads,
and 12 the insulation.
The proper way to set the armature to have it central in the pole pieces
is to have strips of wood or cardboard of the proper thickness and place them
at four equi-distant points between the armature and the pole pieces, which will
make the air space the same all around the armature. Before the metal is
poured in the bearing spaces see that the center of the shaft is in the center of
the bearings, when cap 23 is in place. If it is not, the pillow blocks should be
raised or lowered as the case may be. Remove cap 23 and after the metal is
poured and becomes cool, take out the strips from around the armature and let
the shaft rest in the bearings. Put on the caps and babbitt them, then remove
the pillow blocks and take off the sharp corners of the metal between the caps
and pillow blocks, and cut a groove lengthwise in the babbitt that the oil
may circulate the whole length of the bearings. If the work is well done, the
shaft should run cool, but if it does not, take off the caps and put a piece of
paper between the cap and the bearing.
THE ARMATURE: WIRE AND WINDING.
The wire on the armature should be No. 15 double covered (Brown &
Sharp gauge). There are 24 sections in the armature and 2 layers per section,
making the wire on the armature 4 layers deep. The instructions for insulating
and winding a Siemens armature are given on page 4, Figs. I, II, III.
THE FIELD MAGNETS: WIRE AND WINDING.
The wire on the field magnets is No. 18 (Brown & Sharp gauge).
There are 11 layers on each field, and 93 convolutions to each layer, making
the total number of convolutions on both fields 2.046.
The method of winding and connecting up the machine is shown in dia-
gram 14, page 68.
If a rheostat is needed the instructions for building and connecting are
given in the same diagram for winding and connecting the field magnets.
This machine without changing its construction or armature windings
will make one arc light, but in the place of the No. 18 wire on the fields, put
No. 11 wire, and connect up in series. When wound and connected in this
way it will only require to be run at 1,600 revolutions per minute. The first
machine built from these patterns was to supply current for one arc lamp. The
field wire was changed and it did equally as good service as an incandescent
dynamo, only requiring a higher rate of armature speed.
THIRTY=FIVK LIGHT DYNAMO-
These drawings are for a 35 light, 50 volt, 16 C. P. dynamo ; floor space
20 x 24 inches and 13 inches high, to be run at a speed of 2,200 revolutions
per minute, weight 150 pounds. It will require four horse power to drive this
It is unnecessary to go into a thorough detail of construction, as that
ground has been thoroughly covered in the 4 and 10 light machines, and only
parts that differ from them will be taken up.
In Fig. I is the front elevation. The pole pieces (1) and (2) are 18V4
inches long ; 4 inches wide ; 2V4 inches thick, bored out to 8 inches with a gap
between pole pieces 3V2 inches. The field magnets are of wrought iron 8
inches long ; 3V4 inches diameter, as shown by dotted lines in Fig. II. The
ends of the pole pieces are rounded off to a radius of 2 inches and project over
the field magnets 3 /s inch on the outside, which is sufficient to hold the
insulating washers in place and prevent them from warping. The pole pieces
are secured to the field magnets with a single 3 /4 inch cap screw in each end.
The pole pieces extensions (4 1 ) and (4 2 ) are 1 inch thick, and 3 J /2 inches wide ;
8 inches long on the commutator side ; 5 inches long on the pulley side with
braces as shown in cross section in Fig. I and at (16) and (17) in Fig. III.
The armature is a Gramme ring ; the core is built up of thin iron discs
7V4 inches outside diameter ; 4V4 inches inside diameter, making the iron in the
40 PRACTICAL DYNAMO BUILDING.
core 1V2 inches thick. The two outside discs should be of thicker iron to
prevent bulging out between the arms of the hub ; also to hold them firm while
the armature core is being turned off as it will have to be, as the holes in the
discs are not always in the center, which would make the armature out of round
and it would be impossible to balance it. The core must be balanced before the
copper wire is wound on it and can be done by drilling into the end of the core
on the heavy side instead of trying to build up on the outside of the core, as
that would make the armature out of round. If the armature were out of
round the fields would have to be bored out larger in proportion. That would
mean a great loss as it would increase the average distance between the iron in
the pole pieces and the armature core. The core is built up of alternating rings
of iron and paper until it is 4 inches wide on the face. If the hub is turned up
to a good fit so the rings will just slip on and press each one of the arms in the
hub firmly, they will require no other fastening, as the friction is sufficient to
prevent them from turning. The shaft (16) should be of steel IVd inches in
diameter; llVs inches between bearings, but in the bearings it should be turned
down to 1 inch so it will leave a shoulder on the inside of the bearings to keep
the armature in position without the use of set collars. The shaft should
project 4 inches on the outside of bearing to receive the pulley, which should
be 5 inches in diameter ; 4 1 /2 inch face to receive a 4 inch belt.
The commutator (7) is 4Va inches long ; 3 inches in diameter with lugs
or projections on each segment 8 /s inch wide ; 8 /4 inch long, the lead wires to be
secured to the lugs with screws or the lugs to be slotted and the wires soldered
to them. An axial section of the commutator is shown in Fig. VI. (1) is a
brass sleeve with a flange on one end, the other end threaded to receive nut (4) .
The segments (2) are beveled at each end ; the insulation (3) is concaved to
match. There are 42 segments with mica or vulcanized fibre Vs2 inch thick
between the segments. The inside diameter of the commutator should be at
least Vs inch larger than the core that there may be no danger of the segments
and core coming in contact.
The brush holder yoke (5) as shown in Figs. Ill and VII is of brass 5 /s
inch thick and 8 inches between centers of brush holders with 8 /4 inch holes in
the ends for insulating bushings (12). The bushings (12) are of vulcanized
PRACTICAL DYNAMO BUILDING. 41
fibre 3 /4 inch in diameter, 1 /s inch thick. The brush holders are shaped as shown
at (II) in Figs. Ill and VIII, and are 4 3 /4 inches long. The end going through
the yoke is l /2 inch in diameter for the distance of 1 3 A inches, and is threaded
to receive nut (8) . "Vulcanized fibre or hard rubber washers (3) are placed on
brush holder to insulate it from yoke (5). A brass washer (14) is placed
between the nut and insulating washer to prevent the nut from cutting into the
washer, and also for furnishing a means of connecting the lamp circuit and
field magnet wires to the brush holder. The other end of the brush holder is
slotted as shown in Fig. VIII, the slot being l*/2 x 8 /s inches ; the brush to be
1V2 inches wide ; the gib (3) is placed in the slot between the brush and the
screw (2) ; the gib presenting a larger surface to the brush, holds it more
firmly and prevents the screw from cutting into the brush. The yoke is
secured to the bearing with a collar and washer, and handle (10) serves to
hold the yoke in place when the position of the brushes has been determined.
The pillow blocks (9) are secured to the extension with two */2 inch cap screws
going up from the bottom into the bearings. The pillow block and cap are
cored out around the shaft, to make room for the babbitt metal bearings, which
gives the shaft a wearing surface of 3 inches. From center of shaft to base
of pillow blocks is 5V2 inches. Cap (18) is fitted in between projections in the
pillow blocks and is held in position with two V2 inch cap screws. In fitting
the shaft in the bearings and babbitting them, care should be used that the
armature is perfectly central in the pole pieces. The shaft must be allowed
to revolve freely to prevent heating, but it should not be loose or the armature
The hub (2) of the armature should be of brass, secured to the shaft
with a pin (3), as shown in Fig. IV. In Fig. V. are given the dimensions
of the armature hub with projections for holding the rings in place. The
projections (19) are put on with screws that they may be removed to allow
the rings to be placed on the hub.
ARMATURE: SIZE OF WIRE AND WINDING.
There should be 42 sections in the armature with two layers of wire
to each section ; three convolutions to each layer of ]^o. 12 double covered
copper wire (Brown & Sharp gauge). The winding should start on a line
of the arms so there will be three spaces left on the outside of the armature
just the width of the arms. It is not a good idea to try to fill those spaces
over the spider arms, as it would pile the wire up against the arms on the
inside of the core and would be liable to throw the armature out of balance,
and if it does not, it will make the armature look badly. With 42 sections,
and 6 convolutions per section, the total number of convolutions on the
armature would be 252. With about 13 inches per convolution, the length
of wire on the armature would be 273 feet.
THE FIELD: MAGNETS SIZE OF WIRE AND WINDINGS.
The size of wire on the field magnets should be No. 18 (B. & S. gauge)
10 layers deep ; 135 convolutions per layer, making 2,700 convolutions on both
fields with a total length of about 2,900 feet, making the resistance of the field
coils about 19.5 ohms. What little variation there will be in the length of wire
will not materially affect the machine. The fields are to be connected hi
"shunt." This style of machine has been in use for two years.
PRACTICAL DYNAMO BUILDING.
SIXTY LIGHT DYNAMO.
These drawings are for a 60 light, 16 candle power, 50 volt dynamo ;
floor space 20x28 inches, and 13V2 inches high; armature speed 1,600
revolutions per minute ; weight 500 pounds. It will require about 5 horse
power to drive the dynamo.
Fig. I shows the front elevation. 1 is the upper pole piece ; 3 the lower
pole piece ; 2 the field magnet cores, and 4 the cross section, of pole piece
The pole pieces are 16 3 /4 inches long; 8 inches wide, and 2Va inches
thick. The field magnet cores are 8 inches long ; 8 inches wide and 2V2 inches
thick in the center, and are rounded off at the corners to facilitate winding.
Two holes are cored through the fields to allow the bolts to pass through, as
shown by dotted lines.
In bolting the machine together 4 bolts are used, 2 at each end, the
bolts passing freely through the upper pole piece and field magnet cores. The
lower pole piece is drilled and tapped to receive them.
Fig. II is a plan view of lower pole piece, showing extensions for
supporting the pillow blocks. The extension (4 1 ) on the pulley side is 5V2
inches long ; 4V2 inches wide, and 1 inch thick. On the commutator side, the
extension (4 2 ) is 10 7 /s inches long; 4V2 inches wide, and 1 inch thick with a
46 PRACTICAL DYNAMO BUILDING.
brace, as shown at (4 2 ) Fig. Ill, to strengthen the extension. Only a fillet
is needed on the pulley side, as the bearing is so close to the pole piece.
Fig. Ill shows a vertical section through shaft. The shaft (35) is made
of steel I 1 /* inches in diameter; 28 inches long; 16 8 /s inches between bearings.
In the bearings the shaft is turned down to 1 inch, leaving a shoulder on the
inside of the bearings to prevent endwise play. The shaft should revolve freely
in the bearing and still not be loose; a little endwise play of the shaft say
Vie inch will not do any harm, but if the cap to the bearing does not fit properly
and there is a chance for the shaft to vibrate vertically, it will not only cause
the whole machine to shake and make a pounding noise, but whatever vibration
there is in the bearing will be felt at the brushes ; at every revolution the
brushes will be thrown off the commutator, causing an abnormal spark, which
will soon destroy the brushes and the commutator as well. A great many
machines are working badly to-day from that cause ; that is, machines that
have been in use for a long time. The bearings get a little worn and the
armature may be a little out of balance and the sparking begins so gradually
that it is hard to determine the cause. The result is a continual turning off of
the commutator and constant renewal of brushes, which is not only expensive
but very annoying. The machine is also in danger while working in such a
condition, as the fine particles of copper from the brushes and commutator
pervades every portion of the machine. They work in between the lead wires
where they connect to the segments of the commutator ; also into the armature,
and will eventually short circuit some of the coils, and a burnt-out armature
is the result.
The shaft on the pulley side should extend sufficiently to allow room
for a pulley with a 4 J /2 inch face, as it will require a 4 inch belt to drive the
The bearings (6) are 4 inches wide made of babbitt metal. Before the
metal is poured in the bearing spaces the armature must be placed perfectly
central in the pole pieces. From center of shaft to base of pillow blocks it
PRACTICAL DYNAMO BUILDING. 47
is 5Vs inches. The pillow-blocks are secured to the extensions with four 3 /s
inch bolts going down through the base of pillow blocks into extensions.
The hub for the armature core is of brass and is in two parts, as shown
at 7 and 8, with three radial arms extending out from the center, as shown in
Fig. V. The hubs are first bored out to fit the shaft and the inner surfaces
faced off that they may come together without leaving an opening between
them. They are then slipped on the shaft in place and a pin put through the
hubs and shaft to hold them in position, as shown at 35, Fig. Y. On one side
of the arms are solid lugs extending to the height of the core, on the other side
the lugs are removable, as shown at 10.
The core is built up alternately of thin iron discs and paper 7 J /4 inches
outside diameter and 4V4 inches inside diameter to form a solid ring 8 inches long.
The ends of the arms should be turned off so the discs will slip on tight
but not sufficiently so to warp them out of shape. The two outer discs should
be 3 /ie inch thick. After the discs are placed on the hubs and pressed down,
lugs (10) are replaced and held firmly with screws (11). The object of the
thicker discs on the outside is to prevent the iron discs bulging out between
the arms. If the discs are properly fitted to the arms, they will need no other
fastening, as the friction will be sufficient to hold them from turning.
The shaft should then be put in a lathe and one or two cuts taken off
the outside that the outer surface may be perfectly true and smooth.
The armature should then be placed on parallel strips and perfectly
balanced, which can be done by drilling into the end of the core on the heavy
side until the armature will come to rest at any point.
When insulating the armature core, care should be used that the
insulation is of the same thickness at all points on the outer surface, for if
the insulation is of unequal thickness, the same irregularity will show when
the armature is wound, which will necessitate boring out the pole pieces
enough larger to accommodate the high places, and it will also throw the
copper wire farther from the center in some places than others ; the armature
will thus become unbalanced with very poor chances of correcting the
difficulty. If good results are expected and a smooth, quiet-running machine
is desired, these suggestions must be observed.
48 PRACTICAL DYNAMO BUILDING.
There are 42 segments in the commutator (12). They are 4 1 /* inches
long on the inside ; 3 3 /4 inches on the outside and 1 inch wide ; 13 is the
commutator core; 14, fibre insulation; 10, the nut to hold the commutator
together; 15, a metal washer interposed between the nut and insulation. If
the washer is not used, the friction of the nut on the insulation in tightening
up the commutator is sufficient to twist the segments and leave them spiral
instead of longitudinal with the shaft as they should be. 38 is the air space
between the segments of the commutator (12) and the core (13) ; 37 are the
screws for connecting the lead wires to the segments of the commutator. A
detail of yoke, brush holder, rod and insulation is given in Fig. VII.
Brush holders (24) are constructed so that they may be moved on the
stud bolts and can be set zig-zag so that the whole surface of the commutator
may be in contact and as the commutator wears away, the surface will wear
smooth and not in ridges. Four narrow brushes are used instead of two wide
ones, which is very essential for machine carrying heavy currents, as it insures
better contact on the commutator, and in case the commutator becomes a little
rough or uneven the brushes are less liable to spark.
Brush holders should not be positive on a machine carrying heavy
currents, but should be pressed on with springs that the least wear in either
brush or commutator may be automatically taken up, which not only relieves
the person in charge of a great deal of trouble, but keeps a constant pressure
of the brushes on the commutator at all times. The measurements of the
brushes and holders are given in Fig. VIII.
The collar (18) for securing the brush holder yoke to bearing has been
thoroughly described in previous machines. A detail is given in Fig. IV.
Fig. V shows end view of armature core (9) with dimensions of rings.
Their position is shown at (9) Fig. III.
Fig. VIII shows a side and top view of brush holder (24) with brushes
(27) in position. This is a very easy and convenient holder to make. The
PRACTICAL DYNAMO BUILDING, 49
screw (28) that holds the plate that clamps the brush should always be on the
top side so it will be an easy matter to adjust the brushes when the machine is
running 1 .
It is not necessary in building machines that each separate one shall be
carried out in detail as given in the drawings. There are several different
styles of commutators and brush holders given and any one can be used as it
suits convenience or fancy, or parts of your own inventing can be applied ; so
there is sufficient material used to safely carry the current, and all parts well
and substantially constructed. I would not advise any material change in the
dimensions of the machine or sizes or quantity of wire, unless you wish to do
some experimenting and take these machines as a basis from which to work.
The writer found by building and running these machines what their capacities
were and gives them here just as he found them. They are no toys but
machines that are intended for actual service. The 60 light machine from
which these drawings are made has been used for lighting our shop for the
last two years, and is giving as good service now as the first day it started.
All measurements in the dynamo are given finished and in making
patterns allowance will have to be made for shrinkage and finishing.
THE ARMATURE WIRE AND WINDINGS.
The wire on the armature is "No. 12 B. & S. gauge, double cotton
covered. There are 42 sections with 2 layers per section, 5 convolutions per
layer, making the total number of convolutions on armature 420.
The method of winding and connecting a Gramme ring is given in
Figs. 4 and 5, page 9.
The wire on the fields is No. 15 double cotton covered. There are 13
layers on each field, with 106 convolutions to each layer; total number of
convolutions on both fields, 2,756.
If a 110 volt dynamo is preferred to a 52, the only change that is
necessary in this machine is to put one more layer of wire on the fields ; leave
the armature and balance of the machine as given above, and increase the
armature speed a little, and you will have a 110 volt dynamo.
These drawings are for a 150 light, 110 volt dynamo ; floor space 25 x 38
inches, and 16 3 /s inches high; weight, 1,100 pounds; armature speed 1,350
revolutions per minute. The machine will require 15 horse power to drive it.
Fig. I is a front elevation of the machine. 1 is the upper pole piece ; 2
the lower pole piece, and 3 the field magnet cores. The pole pieces are 22
inches long ; 10 inches wide, and 3 inches thick. The field magnet cores are
10 8 /s inches long; 10 inches wide, and 3V2 inches thick in the center, and
gradually rounded off to the circle of the ends of the pole pieces as shown in
Fig. II. The field magnet cores will then have the same cross sectional area
as the pole pieces. The lower pole piece (Fig. II) is provided with extensions
for supporting the armature bearings. The extension on the pulley side is 6 3 /s
niches long, and 6V2 inches wide ; on the commutator side, the extension is
IS 1 /* inches long, 6V2 inches wide and IVs inches thick. A chipping strip 5
inches wide and V inch thick should be placed on the ends of the extensions
for furnishing surfaces for bearings. Two bolts at each end passing through
upper pole piece and field magnet cores, threaded into lower pole piece, are
required to bolt the machine together. Pole pieces are bored out to lOVie
inches ; gap between them 3 x /2 inches. Too much care can not be taken in
making the joints. The pole pieces should be planed as smooth as possible,
54 PRACTICAL DYNAMO BUILDING.
then with a fine file and scraper remove all the tool marks that the surface may
be perfectly smooth and polished.
The field magnet cores may be finished in a lathe, but unless a strong-
heavy lathe is used and the tool held rigidly, it will spring, and the farther the
cut goes from the center the greater the spring of the tool. After the cut is
finished and a straight edge is placed on the core, it will show that the center
is nearly Vs2 inch lower than the outsides. Those high placed will have to be
taken off with a file with danger of getting them out of true. If the machine
were put together as the cores came out of the lathe, not V* of the iron would
be in contact ; a great loss would be sustained from the increased magnetic
resistance ; the joints would become heated, and it is a question if a dynamo
working under those conditions could be brought up to its rated capacity
without increasing the speed to a dangerous point.
It may appear to the reader that there is too much stress laid on the
forming of the joints of the machine, and that there is too much explaining
about them; but as it has cost the writer a great deal of time and expense, and,
in fact, a good many changes to get the dynamos described in this work up to
the point claimed for them, he can more fully realize the importance of a
thorough explanation. To show the effect of poor workmanship, the writer
will give an instance of a specially constructed machine for slow speed. The
dimensions were as follows : armature (a Gramme ring) 10V2 inches in diameter ;
3 inches wide ; wound 5 layers deep with ~No. 16 wire ; the pole pieces were of
cast iron 3 inches wide at the armature, 4 inches at the field magnets and 2
inches thick. The field magnet cores were of wrought iron 14*/2 inches long ;