[Footnote: Paper read before the Institution of Mechanical
Engineers.--_Engineering_.]
By DANIEL LONGWORTH, of London.
The movable-fulcrum power hammer was designed by the writer about five
and a half years ago, to meet a want in the market for a power hammer
which, while under the complete control of only one workman, could
produce blows of varying forces without alteration in the rapidity with
which they were given. It was also necessary that the vibration and
shock of the hammer head should not be transmitted to the driving
mechanism, and that the latter should be free from noise and liability
to derangement. The various uses to which the movable fulcrum hammers
have been put, and their success in working[1]--as well as the
importance of the general subject which includes them, namely, the
substitution of stored power for human effort--form the author's excuse
for now occupying the time of the meeting.
[Footnote 1: The hammers have been for some years used by A. Bamlett, of
Thirsk; the American Tool Company, of Antwerp; Messrs. W.&T. Avery, of
Birmingham; Pullar & Sons, of Perth; Salter & Co., of West Bromwich;
Vernon Hope & Co., of Wednesbury, etc.; and also for stamps by Messrs.
Collins & Co., of Birmingham, etc.]
Until these hammers were introduced, no satisfactory method had been
devised for altering the force of the blow. The plan generally adopted
was to have either a tightening pulley acting on the driving belt, a
friction driving clutch, or a simple brake on the driving pulley, put in
action by the hand or foot of the workman. Heavy blows were produced
by simply increasing the number of blows per minute (and therefore the
velocity), and light blows by diminishing it--a plan which was quite
contrary to the true requirements of the case. To prevent the shock
of the hammer head being communicated to the driving gear, an elastic
connection was usually formed between them, consisting of a steel spring
or a cushion of compressed air. With the steel spring, the variation
which could be given in the thickness of the work under the hammer was
very limited, owing to the risk of breaking the spring; but with the
compressed air or pneumatic connection the work might vary considerably
in thickness, say from 0 to 8 in. with a hammer weighing 400lb. The
pneumatic hammers had a crank, with a connecting rod or a slotted
crossbar on the piston-rod, a piston and a cylinder which formed the
hammer-head. The piston-rod was packed with a cup leather, or with
ordinary packing, the latter required to be adjusted with the greatest
nicety, otherwise the piston struck the hammer before lifting it, or
else the force of the blow was considerably diminished. As the piston
moved with the same velocity during its upward and downward strokes,
and, in the latter, had to overtake and outrun the hammer falling under
the action of gravity, the air was not compressed sufficiently to give
a sharp blow at ordinary working speeds, and a much heavier hammer was
required than if the velocity of the piston had been accelerated to a
greater degree.
As it is impossible in the limits of this paper to describe all the
forms in which the movable fulcrum hammers have been arranged, two types
only will be selected taken from actual work; namely, a small planishing
hammer, and a medium-sized forging hammer.[1]
[Footnote 1: To the makers, Messrs. J. Scott Rawlings & Co, of
Birmingham, the author is indebted for the working drawings of these
hammers.]
The small planishing hammer, Figs. 1 to 3, next page, is used for
copper, tin, electro, and iron plate, for scythes, and other thin work,
for which it is sufficient to adjust the force of the blow once for all
by hand, according to the thickness and quality of the material before
commencing to hammer it. The hammer weighs 15 lb., and has a stroke
variable from 2½ in. to 9½ in., and makes 250 blows per minute. The
driving shaft, A, is fitted with fast and loose belt pulleys, the belt
fork being connected to the pedal, P, which when pressed down by the
foot of the workman, slides the driving belt on to the fast pulley and
starts the hammer; when the foot is taken off the pedal, the weight on
the latter moves the belt quickly on to the loose pulley, and the hammer
is stopped. The flywheel on the shaft, A, is weighted on one side,
so that it causes the hammer to stop at the top of its stroke after
working; thus enabling the material to be placed on the anvil before
starting the hammer. The movable fulcrum, B, consists of a stud, free to
slide in a slot, C, in the framing, and held in position by a nut and
toothed washer. On the fulcrum is mounted the socket, D, through which
passes freely a round bar or rocking lever, E, attached at one end to
the main piston, F, of the hammer, G, and having at the other extremity
a long slide, H, mounted upon it. This slide is carried on the
crank-pin, I, fastened to the disk, J, attached to the driving shaft, A.
The crank-pin, in revolving, reciprocates the rocking lever, E, and
main piston, F, and through the medium of the pneumatic connection, the
hammer, G. The slide, H, in revolving with the crank-pin, also moves
backward and forward along the rocking lever, approaching the fulcrum,
B, during the down-stroke of the hammer, and receding from it during
the up-stroke. By this means the velocity of the hammer is considerably
accelerated in its downward stroke, causing a sharp blow to be given
while it is gently raised during its upward stroke.
To alter the force of the blow, the hammer, G, is made to rise and fall
through a greater or less distance, as may be required, from the fixed
anvil block, K, after the manner of the smith giving heavy or light
blows on his anvil. It is evident that this special alteration of the
stroke could not be obtained by altering the throw of a simple crank and
connecting rod; but by placing the slot, C, parallel with the direction
of the rocking lever, E, when the latter is in its lowest position, with
the hammer resting on the anvil, and with the crank at the top of its
stroke, this lowest position of the rocking lever and hammer is made
constant, no matter what position the fulcrum, B, may have in the slot,
C. To obtain a short stroke, and consequently a light blow, the fulcrum
is moved in the slot toward the hammer, G; and to produce a long stroke
and heavy blow the fulcrum is moved in the opposite direction.
Fig. 3 gives the details of the pneumatic connection between the main
piston and the hammer, in which packing and packing glands are dispensed
with. The hammer, G, is of cast steel, bored out to fit the main piston,
F, the latter being also bored out to receive an internal piston, L. A
pin, M, passing freely through slots in the main piston, F, connects
rigidly the internal piston, L, with the hammer, G. When the main piston
is raised by the rocking lever, the air in the space, X, between the
main and internal pistons, is compressed, and forms an elastic medium
for lifting the hammer; when the main piston is moved down, the air in
the space, Y, is compressed in its turn, and the hammer forced down to
give the blow. Two holes drilled in the side of the hammer renew the air
automatically in the spaces, X and Y, at each blow of the hammer.
Figs. 4 to 6, on the next page, represent the medium size forging
hammer, for making forgings in dies, swaging and tilting bars, and
plating edged tools, etc.
The hammer weighs 1 cwt., has a stroke variable from 4 in. to 14½ in.,
and gives 200 blows per minute; the compressed air space between the
main piston and the hammer is sufficiently long to admit forgings up to
3 in. thick under the hammer.
To make forgings economically, it is necessary to bring them into the
desired form by a few heavy blows, while the material is still in a
highly plastic condition, and then to finish them by a succession of
lighter blows. The heavy blows should be given at a slower rate than the
lighter ones, to allow time for turning the work in the dies or on the
anvil, and so to avoid the risk of spoiling it. In forging with the
steam hammer the workman requires an assistant, who, with the lever
of the valve motion in hand, obeys his directions as to starting and
stopping, heavy or light blows, slow or quick blows, etc; the quickest
speed attainable depending on the speed of the arm of the assistant.
In the movable-fulcrum forging hammer the operations of starting and
stopping, and the giving of heavy or light blows, are under the complete
control of one foot of the workman, who requires therefore no assistant;
and by properly proportioning the diameter of the driving pulley and
size of belt to the hammer, the heavy blows are given at a slower rate
than the light ones, owing to the greater resistance which they offer to
the driving belt.
In this hammer the pneumatic connection, the arrangements for the
starting, stopping, and holding up of the hammer, as well as those for
communicating the motion of the crank-pin to the hammer by means of
a rocking lever and movable fulcrum, are similar to those in the
planishing hammer, differing only in the details, which provide double
guides and bearings for the principal working parts.
[Illustration: LONGWORTH'S POWER HAMMER WITH MOVABLE FULCRUM.]
The movable fulcrum, B, Figs. 4 and 5, consists of two adjustable steel
pins, attached to the fulcrum lever, Q, and turned conical where they
fit in the socket, D. The fulcrum lever is pivoted on a pin, R, fixed in
the framing of the machine, and is connected at its lower extremity
to the nut, S, in gear with the regulating screw, T. The to-and-fro
movement of the fulcrum lever, Q, by which heavy or light blows are
given by the hammer, is placed under the control of the foot of the
workman, in the following manner: U is a double-ended forked lever,
pivoted in the center, and having one end embracing the starting pedal,
P, and the other end the small belt which connects the fast pulley
on the driving shaft, A, with the loose pulley, V, or the reversing
pulleys, W and X. These are respectivly connected with the bevel wheels,
W_{1}, and X_{1}, gearing into and placed at opposite sides of the bevel
wheel, Z, on the regulating screw in connection with the fulcrum lever.
When the workman places his foot on the pedal, P, to start the hammer,
he finds his foot within the fork of the lever, U; and by slightly
turning his foot round on his heel he can readily move the forked
lever to right or left, so shifting the small belt on to either of the
reversing pulleys, W or X, and causing the regulating screw, T, to
revolve in either direction. The fulcrum lever is thus caused to move
forward or backward, to give light or heavy blows. By moving the forked
lever into mid position, the small belt is shifted into its usual place
on the loose pulley, V, and the fulcrum remains at rest. To fix the
lightest and heaviest blow required for each kind of work, adjustable
stops are provided, and are mounted on a rod, Y, connected to an arm of
the forked lever. When the nut of the regulating screw comes in contact
with either of the stops, the forked lever is forced into mid position,
in spite of the pressure of the foot of the workman, and thus further
movement of the fulcrum lever, in the direction which it was taking,
is prevented. The movable fulcrum can also be adjusted by hand to any
required blow, when the hammer is stopped, by means of a handle in
connection with the regulating screw.
In conclusion the author wishes to direct attention to the fact, that in
many of our largest manufactories, particularly in the midland counties,
foot and hand labor for forging and stamping is still employed to an
enormous extent. Hundreds of "Olivers," with hammers up to 60 lb. in
weight, are laboriously put in motion by the foot of the workman, at a
speed averaging fifty blows per minute; while large numbers of stamps,
worked by hand and foot, and weighing up to 120 lb., are also employed.
The low first cost of the foot hammers and stamps, combined with the
system of piece work, and the desire of manufacturers to keep their
methods of working secret, have no doubt much to do with the small
amount of progress that has been made; although in a few cases
competition, particularly with the United States of America, has forced
the manufacturer to throw the Oliver and hand-stamp aside, and to employ
steam power hammers and stamps. The writer believes that in connection
with forging and stamping processes there is still a wide and profitable
field for the ingenuity and capital of engineers, who choose to
occupy themselves with this minor, but not the less useful, branch of
mechanics.
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