induced current set up in the coils thus short circuited. The result would be
the destruction of that coil, and no doubt the neighboring coils ; the whole
armature would then have to be rewound. The cause of all the trouble being
in the commutator, if not corrected, the second armature would share the same
fate. The joining together of the field magnets and pole pieces, the adjusting
of the armature and bearings are secondary considerations compared with
the building of the armature and commutator. A little carelessness in the
construction of either one will be sufficient to prevent the machine from
working ; the work will have to be done over again, which is usually harder
18 PRACTICAL DYNAMO BUILDING.
to do than to build in the first place, to say nothing of the annoyance and
disappointment of the machine not working properly. The writer has a
machine now in use from which these drawings are made, and any one
building from these instructions should be able to get the same results.
The pillow-blocks (2) are l : /2 inches wide at the base ; Va inch thick ;
from center of shaft to base of pillow-block is 2 3 /s inches. Instead of
babbitting the bearings, bushings are used, one of which is shown at 9.
They are made of brass 1V4 inches long ; 5 /s inch in diameter with a 3 /s inch
hole through center to receive the shaft. It is secured to the pillow block with
a screw, as shown at 5, Fig. IV. The screw should go through the bushing
instead of pressing on the outside, for in that case there would be danger of
compressing the bushing and heating the shaft. The object of using bushings
is to facilitate repairs. In case of wear in the bearings, the bushings can be
removed and new ones supplied without the danger of getting the armature out
of center, as would be the case if the bearings were babbitted. The bushing on
the commutator side also serves to hold the yoke and allows it free movement
to determine the position of the brushes on the commutator.
The shaft (11) should be of steel 10 inches long, and 3 /s inch in diameter.
The pulley is 2 niches in diameter, 1V4 inch face. It can be made of wood with
a metal bushing to secure it to the shaft.
The brush holder yoke (4) is made of vulcanized fibre 3 inches long ;
V4 inch thick; 2 l /z inches between centers of brush holders cut to shape, as
shown at 4 in Fig. IV. A brass yoke can be used if preferred like the one
shown in the 10 light machine, but insulating bushings and washers will have
to be used which will cause a great deal more labor with no better results, as I
have found in small machines that a fibre yoke answers all purposes.
The brush holders (5) are of 3 /g inch square brass ; ! 3 /4 inches long,
turned on one end for the distance of 9 /ie inch to go through the yoke and
threaded to receive the nut (7) . A brass washer (8) is interposed between the
nut (7) and the yoke (4). To the washer are attached the wires from the
field magnets and lamp circuits. The other end of the brush holder is slotted
to receive the brush (6). A screw (10) is put through the end of the holder
to clamp the brush and hold it firmly.
PRACTICAL DYNAMO BUILDING. 19
The brushes (6) are made of several layers of thin sheet spring 1 copper,
thick enough to make a good contact on two sections of the commutator, while
the insulation between the sections is passing the brushes. If a good contact is
not made by the brushes on the commutator there will be an excessive sparking
and a rapid destruction of the brushes and commutator.
A handle (10) as shown in Fig. IV serves to hold the yoke in place
after the position of the brushes has been determined. It is made of wood
with a screw in the end. A hole is drilled and tapped in the yoke. The handle
should be screwed down sufficiently to hold the yoke, but not enough to
compress the bushing, or it will cause the shaft to heat.
THK FIELD MAGNETS.
On each end of the field magnet cores should be placed a fibre washer
Vs inch thick, or 2 thicknesses of cardboard will answer as well. The washers
must be well fitted to the magnet cores and held there firmly to prevent the
wire from pressing them out of position while the magnet is being wound. The
magnet cores should then be covered with two layers of adhesive rubber tape or
several layers of muslin or manilla paper well shellaced. They are now ready
for the copper wire, which is of double covered 'No. 20 (Brown & Sharp gauge)
11 layers deep ; 80 convolutions per layer, making 880 convolutions on each
field or 1,760, convolutions on both fields, with a total length of about 1,200 feet,
and a resistance of nearly 13 ohms. The length of wire may vary a little
from the figures given, caused by the difference in the thickness of insulation,
but the variation will not be enough to make any difference with the working
of the machine. The method of winding and connecting up the circuits is
given in diagram 14, page 68.
These drawings are for a 10 light, 50 volt, 16 C. P. dynamo; floor
space 18x12 inches and 7*/2 inches high, to be run at a speed of 2,200
revolutions per minute, weight 75 pounds. It will require one horse power to
drive this dynamo.
In Fig. I is shown the upper pole piece (1) ; lower pole piece (3) ; field
magnet cores (2) and cross section of lower pole piece extension for supporting
the pillow blocks (4). The pole pieces (1) and (3) are 10 inches long, 4 J /2
inches wide, l a /4 inches thick. The gap between the pole pieces is ! 5 /s inches.
3 /s inch hexagon cap screws (5) are used to secure the pole pieces (1) and (3)
to the field magnet cores (2). Pole pieces are to be bored out to 5 niches.
Soft gray cast iron should be used for pole pieces and field magnet cores.
Great care must be taken in putting the machine together at the points where
the pole pieces and field magnets join. The surface should be planed smooth,
then scraped that the whole surface of the iron may be in contact without
depending on the screws to make a good joint. The joints are the weakest
points in the machine and quite a loss is sustained with the best possible
Fig. II shows the lower pole piece (3) with extensions (4) and (4") for
supporting the pillow blocks (3). The extension (4') on the pulley side is 3*/2
inches long and 2V2 inches wide. On the commutator side, the extension (4")
is 5 3 A inches long ; 2V2 inches wide and J /2 inch thick. A. brace or rib is shown
in cross section (4) Fig. I.
PRACTICAL DYNAMO BUILDING.' 23
Fig. Ill shows the armature core (1) ; shaft (2) and pin (4) through
the shaft for holding the commutator in position. The armature spool is made
of well seasoned maple wood, 4*/2 inches long ; inside diameter 2V inches ;
diameter of flanges 4 3 /s inches ; thickness of flanges 3 /i6 inch. A pin (3) shown
by dotted lines, is put through the spool and shaft to securely hold the armature
in position. The spool should be finished on the shaft that it may be perfectly
true and is then wound full of annealed iron wire with a layer of paper between
the layers of wire. The shaft (2) should be made of steel 5 /s inch diameter;
17 3 /s inches long. On the commutator side the shaft should extend 6 3 /s inches
from the armature core ; on the pulley side, 6V2 inches.
Fig. IY shows the commutator (1) ; shaft (2) ; pillow blocks (3) ; brush
holder yoke (5) ; bushing (6) ; brush holder (7) ; nut (8) ; brass washer (9) ;
insulating washer (10) and insulating bushing (11), all in position. (3) is a
side view of the pillow block, which is 1 inch thick ; ! 3 /4 inches at shaft. The
dotted lines show the bushing (6) and the mode of holding the brush holder
yoke (5). The insulating bushing (11) is of vulcanized fibre, or well seasoned
maple wood may be used 5 /g inch outside diameter, and Vi inch inside, fitting
into yoke (5). Insulating washer (10) can be made of fibre or hard rubber 1
inch in diameter ; Vs inch thick with V4 inch hole in center to slip on the
holder. (7). One washer is placed on each side of yoke. On the outside of
washer (10) is a brass washer (9) serving the two purposes of fastening for the
field wires and preventing nut (8) from cutting into insulating washer (10).
Fig. Y shows end view of pillow block (3) ; side view of brush holder
yoke (5) ; handle (4) ; screw (7) for holding bushing (6). The base of pillow
block (3) is 2V-2 inches wide and 2 15 /ie inches from center to base. The bushing
(6) is fitted into pillow block (3) and screw (7) is put through the head of the
24 PRACTICAL DYNAMO BUILDING.
pillow block and through the bushing (6) to hold it in position. The object of
putting the screw through the bushing is to prevent the compressing of the
bushing and causing the shaft to heat. The yoke (5) is made of brass ; it is
4Va inches between centers of brush holder (7) . Handle (4) is made of wood
with a screw in the end ; the screw to go through yoke (5) and press on bushing
(6) . After the position of the brushes on the commutator has been determined,
turn the handle until the screw presses tightly on the bushing, but not hard
enough to compress the bushing and heat the shaft.
In Fig. VI is shown the bushing (6) and brush holder (7). The bushing
is made of brass 2 l /i inches long ; ~/s inch outside diameter with a 5 /s inch hole
to fit the shaft. A flange 1V2 inches in diameter is left on the inside to hold
yoke (5) in place. The brush holder (7) is of brass 2 x /2 inches long; J /2 inch
square, turned down on one end for the distance of IVs inches to go through
yoke and threaded to receive nut. Through the other end is a slot Vs x 3 /4
inches to receive brush. The thumb nut (8) holds the brush firmly in place.
In Fig. VII is shown the construction of the commutator, one of the
most essential features of the machine. Take a piece of vulcanized fibre l x/ 2
inches long ; ! 5 /s inches in diameter, and force over it a brass ring 3 /i6 inch thick,
then space off into 24 sections and put a screw through the end of each section
as shown at (12). Then with a fine hack saw cut through the ring between
the rows of screws, being careful to cut clear through the ring to the fibre and
remove all brass cuttings from the slot. Then fill the slot with thin sheet fibre.
The commutator must not be turned off until in position on the shaft. If any
of the brass cuttings are allowed to remain in the slots between the sections, it
will short circuit the coil attached to that segment ; the result will be an induced
current set up in that coil, which would soon destroy it and no doubt the
THE ARMATURE CONSTRUCTION AND WINDINGS.
This armature is the Siemens type. When the spool for the armature
core is turned to size and secured to the shaft, space off the flanges into 24
parts, being 1 careful that the spaces in both flanges are directly in line with the
shaft. Then with a fine saw cut into the flanges to the depth of V* inch to
receive division pins. The pins may be made of vulcanized fibre or wood, and
should project 1 A inch above the flanges. The object of the pins is to keep the
layers of copper wire in their proper position. Then wind the spool full of !N"o.
18 annealed iron wire with a layer of paper between each layer of wire. The
outer end of the iron wire should be soldered to prevent unwinding. Then
cover the wire and the shaft at each end of armature for the distance of 2
inches with two layers of adhesive rubber tape and the armature is ready for
the copper wire, which is No. 18 Brown & Sharp gauge.
Starting from the commutator end of the armature, the wire is carried
along the surface of the armature core between two division pins parallel with
the shaft ; then across the end of the armature core between the division pins
diametrically opposite those on the other side of the armature ; then across the
commutator end of the core and alongside of the first wire, and so on until
there are ten convolutions on one side of the shaft; then go around the
armature again in the same manner, crossing the ends of the core on the
opposite side of the shaft ; then there will be 20 convolutions called 1 section.
Do not cut the wire but leave a loop about five inches long to go to the
commutator. Those are called lead wires. After making the loop and securing
the wires together close to the armature core, lay the wire along armature core
in the next space as before. Continue thus until 12 sections are laid on. This
9(5 PRACTICAL DYNAMO BUILDING.
is the inner layer. All the spaces on the core have two layers of wire but there
are only twelve lead wires. The outer layer is then started on top of the inner
layer and goes around the core as in starting. There will be four layers of wire
between each row of pins but only two sections Avith the lead wire for each
section on opposite sides of the core. The copper wire all being laid on the
core, the next step is to bind the copper wire that it may not be thrown out of
place from the high rate of speed the armature has to revolve. The bands
should be three in number of ~No. 22 spring brass wire drawn as tightly as the
wire will stand without breaking and each should be soldered at several points.
A layer of mica or rubber tape should be between the brass and copper wire.
The field magnets are 5 inches long ; 4 ! /2 inches wide ; I 1 /* inches thick.
They should be of soft gray cast iron and should be secured at each end to the
pole pieces with two 3 /s inch hexagon cap screws, as shown in Fig. I. At the
points where the pole pieces and field magnets join, the parts should be planed
smooth, then scraped so that a perfect joint is made and all the iron touches, as
there is quite a loss sustained with the best possible joint, and the poorer joint
the greater the loss. The best way to put the machine together is to first bolt
the field magnets to the lower pole piece, then place the upper pole piece in
position and carefully examine the joints to see if the iron touches the whole
surface ; if not, it should be made to do so. Do not try to spring them into
position with the bolts. On each end of the field magnets should be placed a
vulcanized fibre washer 1 /s inch thick extending out from the magnet 5 /s inch.
The field magnets should then be covered with two layers of adhesive rubber
tape or several layers of muslin thoroughly saturated with shellac. The
magnets are then ready to wind. The wire to use is ~No. 20 Brown & Sharp
gauge double covered, ten layers to each field magnet with 95 convolutions to
each layer, making 1,900 convolutions on both fields, with a total length of
wire about 1,900 feet, with a resistance of about 20 Ohms. The length of
wire may vary somewhat from the figures given, because of the difference of the
thickness of insulation, or the wire may not be laid closely, so that a few turns
may be lost ; the variation will not be enough to materially change the output
of the machine. Before starting to wind the field magnets coils, a hole should
28 PRACTICAL DYNAMO BUILDING.
be drilled through the fibre washer almost to the iron. The end of the wire
should go through the washer that a connection can be made to lead to the
brushes. It is better to lead out a flexible wire as there is not so much danger
of breaking in handling. If the wire should be broken off close to the fibre,
it would necessitate unwinding the whole field to get the end again.
FIFTEEN LIGHT DYNAMO.
These drawings are for a 15 light, 16 candle power, 50 volt dynamo.
The machine will require a floor space of 24 x 14 inches ; is 9 inches high ;
armature speed 2,500 revolutions per minute, and will require 1V2 horse power
to drive it.
Fig. I is a front elevation of the upper pole piece (1) ; lower pole piece
(3) ; field magnet cores (2), and cross section of pole piece extension f4).
The pole pieces are of cast iron 10 3 /4 inches long ; 6 inches wide ; 1V2
inches thick ; gap between pole pieces 2 3 /s inches. The bore of the pole piece
is 5 x /4 inches.
It is entirely unnecessary to bore out the pole pieces of these small
machines if a close calculation in building the armatures is made, and it
corresponds with the circle of the pole pieces. The armature should be finished
before the machine is put together and if the circles of the armature and pole
pieces are concentric, all that is necessary is to make the proper allowance on
the length of the field .magnet cores for the air space between the armature and
pole pieces. It will make no difference in the working of the machine whether
or not the iron in the pole pieces presents a sand or a finished surface.
The field magnet cores (2) are of cast iron 5 1 /* inches long ; 6 inches
wide and IVa inches thick with the corners rounded off to facilitate winding. A
hole is cored through the center to admit a 3 A inch bolt, and a hole is drilled
through the end of the upper pole piece to correspond, the lower pole piece
PRACTICAL DYNAMO BUILDING.
PRACTICAL DYNAMO BUILDING. 31
being drilled and tapped. There will be only one bolt at each end. This
makes a very quick and convenient way of putting the machine together. The
field magnets should be faced off in a lathe that the ends may be true with the
hole in the center.
Fig. II shows a plan view of lower pole piece with extensions for
supporting the pillow blocks and bearings. The extension (4 1 ) on the pulley
side is 5 inches long ; 3 inches wide with the end rounded off to a radius of l x /2
inches. The extension (4 2 ) on the commutator side is 10 7 /s inches long; 3
inches wide, and 7 /s inch thick with the end rounded of to the same radius.
Fig. Ill shows a vertical section through armature shaft. 1 is the
upper pole piece, and 3 is the lower pole piece showing extensions (4 1 ) and
(4 2 ) ; also the method of securing the pillow blocks to the extensions. One
bolt can be used as is shown in Fig. Ill, but if it should become loosened from
any cause, the shaft would cramp in its bearings and become heated. The
better plan is to use two bolts or screws as is shown in Fig. II.
The distance from top of base to center of shaft is 3 3 /s inches ; the
pillow blocks are cored out to receive babbitt metal bearings, as shown at 27.
The cap (32), Fig. IV, is secured to the pillow block with two half inch
hexagon cap screws (33).
The shaft (31) should be made of steel 23 inches long and 1 inch in
diameter. In the bearings the shaft is turned down to 3 /4 of an inch, leaving a
shoulder to prevent endwise play without the use of set collars. The distance
between bearings is 13 7 /s inches.
The armature core is of soft iron wire wound in a spool of well seasoned
maple wood (7), 6 inches long. The flanges on each end are 4V2 inches in
diameter and 3 /i6 inch thick ; inside diameter of the spool is 2V2 inches. It
should be finished on the shaft, that it may be perfectly true. A V inch steel
32 PRACTICAL DYNAMO BUILDING.
pin should be put through the spool and shaft (as shown at 9) to keep the
armature in position and prevent its turning on the shaft.
Space the flanges into 24 sections and with a fine saw cut a slot to the
depth of a quarter of an inch to receive division pins, as shown at 10, Figs. Ill
and Y. Before placing the division pins in position, wind the spool full of
No. 18 annealed iron wire, as shown, at 8, and the armature is ready for the
insulation. The instructions for insulating and winding a Siemens armature
are given in Figs. I, II, III, pages 4 and >.
It may seem to a casual observer that it is a very easy matter to wind a
spool of iron wire and have it round, smooth and perfectly balanced, but it is
not as easy as it looks.
It can be done by commencing the layers each time at the same end of
the spool, allowing the wire to rest in the grooves of the preceding layer.
This will necessitate cutting and soldering the wire at the end of each layer.
Or the wire can be wound on continuously by placing heavy stiff paper between
each layer of wire to keep it from dropping into the grooves between the
convolutions of the Dreceding layer, and giving an even surface on which to
wind each layer.
The commutator (11) is very easy to build and makes a very nice one
for a small machine. In place of the brass core with a nut for compressing
the segments and holding them in position, 4 bolts are used, as shown at 14.
Two brass heads ,(13), turned concave, are shown in section Fig. I, of which
13, Fig. YII, is an end view. 12, Fig. YII, shows the end insulation, which
can be of fibre rings or mica, either one will readily take the concave form of
the brass washers on the ends of the commutator. 8 /32 inch is of sufficient
thickness for the end insulation. Mica or fibre insulation Vs2 inch thick is used
to insulate the segments from each other. After the segments have all been
arranged with the insulation between them well shellaced, an iron band should
be forced over the segments to draw them as closely together as possible. The
ring should be somewhat smaller than the commutator in its loose condition and
forced over by putting it in a vise or with a bolt from the center with a large
washer at each end. Put the end washers on the shaft or a mandril the exact
size of the shaft with the commutator in the center, then with the bolts set the
PRACTICAL DYNAMO BUILDING. 33
washers up firmly. Take off the ring from the outside and the commutator is
finished with the exception of turning off the outside, which should not be done
until the commutator is placed in its proper position on the shaft so it will be
The lead wires from the armature may be secured to the commutator
segments by screws or soldering, whichever is the most convenient. Soldering
is far the safer, as there is danger of the screws becoming loosened, breaking
off or becoming corroded, causing the brushes to spark, the commutator to
burn and greatly increasing the internal resistance of the machine.
The yoke (16) is of brass 3 /s inch thick, with 5Va inches between centers
of brush holders. A hole in center 2 inches in diameter fits on the collar (17)
that secures the yoke to the bearing (6) . The handle (34) serves to hold the
yoke in position.
The brush holders (19) are of a style that is quite easy to make as they
can be cast in shape and finished with a file with very little labor except wiiere
they go through the yoke. They should be turned to 8 /s inch in diameter for
the distance of I 1 /* inches and threaded to receive nut (20). An insulating
bushing (23-) goes through the yoke and a hard rubber or fibre washer (22)
is placed on the brush holder on either side to insulate the holder from the yoke.
A brass washer (21) is placed between the nut and outside washer, to which
the lamp circuit and field magnet wires are attached.
Fig. IY shows the bearing on the commutator side with cap (32) and
screws (33) ; also the method of attaching the collar (17) for supporting yoke
(16). The holes (28) in the pillow block (6) are drilled and tapped. The
holes (28) in collar (17) are large enough to permit the screws to pass through
freely and are counter sunk so that the screw heads may be flush with the face
of the collar. After securing collar (17) to the pillow block, the yoke is
placed in position and washer (18) is placed on the outside and held in place
with screws (29) . By this arrangement the yoke is allowed to revolve freely
around the shaft for the purpose of changing the position of the brushes and
34 PRACTICAL DYNAMO BUILDING.
at the same time keeping the points of the brushes concentric with the armature
shaft, which is a very essential feature. The brushes should touch segments in
the commutator that are diametrically opposite each other. There should
always be an even number of sections in an armature, that an equal division can
be made, as the current divides at the brushes when it enters the armature, and
joins again at the other brush. As electricity will always take the path of the
least resistance, if there is an unequal number of sections in the armature, or
the brushes set so there are two or three sections less on one side, more current
will flow through one side than the other, causing the armature to heat, the
brushes to spark and the machine to work bad generally, and no doubt in a
short time the destruction of the armature would result.
Fig. Y shows the armature core (7) giving the necessary dimensions,
and showing the method of placing the division pins (10).