WORKSHOP MACHINERY
THE LATHE--PLANING MACHINES--THE STEAM HAMMER--HYDRAULIC
TOOLS--ELECTRICAL TOOLS IN THE SHIPYARD
"When I first entered this city," said Mr. William Fairbairn, in an
inaugural address to the British Association at Manchester in 1861,
"the whole of the machinery was executed by hand. There were neither
planing, slotting, nor shaping machines, and with the exception of
very imperfect lathes and a few drills, the preparatory operations of
construction were effected entirely by the hands of the workmen. Now,
everything is done by machine tools, with a degree of accuracy which
the unaided hand could never accomplish. The automaton, or self-acting,
machine tool has within itself an almost creative power; in fact, so
great are its powers of adaptation, that there is no operation of the
human hand that it does not imitate."
If such things could be said with justice forty-five years ago, what
would Mr. Fairbairn think could he see the wonderful machinery with
which the present-day workshop is equipped--machinery as relatively
superior to the devices he speaks of as they were superior to the
unaided efforts of the human hand? Invention never stands still.
The wonder of one year is on the scrap-heap of abandoned machines
almost before another twelve months have passed. Some important detail
has been improved, to secure ease or economy in working, and a more
efficient successor steps into its place. In his curious and original
_Erewhon_, Mr. Samuel Butler depicts a community which, from the fear
that machinery should become _too_ ingenious, and eventually drain away
man's capacity for muscular and mental action, has risen in revolt
against the automaton, broken up all machines which had been in use for
less than 270 years--with the exception of specimens reserved for the
national museums--and reverted to hand labour. His treatment of the
dangers attending the increased employment of lifeless mechanisms as a
substitute for physical effort does not, however, show sympathy with
the Erewhonians; since their abandonment of invention had obviously
placed them at the mercy of any other race retaining the devices so
laboriously perfected during the ages. And we, on our part, should be
extremely sorry to part with the inanimate helpers which in every path
of life render the act of living more comfortable and less toilsome.
So dependent are we on machinery, that we owe a double debt to the
machines which create machines. A big factory houses the parents
which send out their children to careers of usefulness throughout the
world. We often forget, in our admiration of the offspring, the source
from which they originated. Our bicycles, so admirably adapted to
easy locomotion, owe their existence to a hundred delicate machines.
The express engine, hurrying forward over the iron way, is but an
assemblage of parts which have been beaten, cut, twisted, planed,
and otherwise handled by mighty machines, each as wonderful as the
locomotive itself. But then, we don't see these.
This and following chapters will therefore be devoted to a few peeps at
the great tools employed in the world's workshops.
If you consider a moment, you will soon build up a formidable
list of objects in which circularity is a necessary or desirable
feature--wheels, shafts, plates, legs of tables, walking-sticks,
pillars, parts of instruments, wire, and so on. The Hindu turner, whose
assistant revolves with a string a wooden block centred between two
short spiked posts let into the ground, while he himself applies the
tool, is at one end of the scale of lathe users; at the other, we have
the workman who tends the giant machine slowly shaping the exterior of
a 12-inch gun, a propeller shaft, or a marble column. All aim at the
same object--perfect rotundity of surface.
The artisans of the Middle Ages have left us, in beautiful balusters
and cathedral screens, ample proofs that they were skilled workmen
with the TURNING-LATHE. At the time of the Huguenot persecutions large
numbers of French artificers crossed the Channel to England, bringing
with them lathes which could cut intricate figures by means of wheels,
eccentrics and other devices of a comparatively complicated kind. The
French had undoubtedly got far ahead of the English in this branch
of the mechanical arts, owing, no doubt, to the fact that the French
_noblesse_ had condescended to include turnery among their aristocratic
hobbies.
With the larger employment of metal in all industries the need for
handling it easily is increased. Much greater accuracy generally
distinguishes metal as compared with woodwork. "In turning a piece of
work on the old-fashioned lathe, the workman applied and guided his
tool by means of muscular strength. The work was made to revolve, and
the turner, holding the cutting tool firmly upon the long, straight,
guiding edge of the rest, along which he carried it, and pressing
its point firmly against the article to be turned, was thus enabled
to reduce its surface to the required size and shape. Some dexterous
turners were able, with practice and carefulness, to execute very
clever pieces of work by this simple means. But when the article to be
turned was of considerable size, and especially when it was of metal,
the expenditure of muscular strength was so great that the workman soon
became exhausted. The slightest variation in the pressure of the tool
led to an irregularity of surface; and with the utmost care on the
workman's part, he could not avoid occasionally cutting a little too
deep, in consequence of which he must necessarily go over the surface
again to reduce the whole to the level of that accidentally cut too
deep, and thus possibly the job would be altogether spoiled by the
diameter of the article under operation being made too small for its
intended purpose."[5]
Any modern worker is spared this labour and worry by the device known
as the SLIDE-REST. Its name implies that it at once affords a rigid
support for the tool, and also the means of traversing the tool in a
straight line parallel to the metal face on which work is being done.
The introduction of the slide-rest is due to the ingenuity of Mr.
Henry Maudslay, who, at the commencement of the nineteenth century, was
a foreman in the workshop of Mr. Joseph Bramah, inventor of the famous
hydraulic press and locks which bear his name. His rest could be moved
along the bed of the lathe by a screw, and clamped in any position
desired. Fellow-workmen at first spoke derisively of "Maudslay's
go-cart"; but men competent to judge its real value had more kindly
words to say concerning it, when it had been adapted to machines of
various types for planing as well as turning. Mr. James Nasmyth went so
far as to state that "its influence in improving and extending the use
of machinery has been as great as that produced by the improvement of
the steam-engine in respect to perfecting manufactures and extending
commerce, inasmuch as without the aid of the vast accession to our
power of producing perfect mechanism which it at once supplied, we
could never have worked out into practical and profitable forms the
conceptions of those master minds who, during the last half century,
have so successfully pioneered the way for mankind. The steam-engine
itself, which supplies us with such unbounded power, owes its present
perfection to this most admirable means of giving to metallic objects
the most precise and perfect geometrical forms. How could we, for
instance, have good steam-engines if we had not the means of boring out
a true cylinder, or turning a true piston-rod, or planing a valve face?
It is this alone which has furnished us with the means of carrying
into practice the accumulated results of scientific investigation on
mechanical subjects."
The screw-cutting lathe is so arranged that the slide-rest is moved
along with its tool at a uniform speed by gear wheels actuated by the
mechanism rotating the object to be turned. By changing the wheels the
rate of "feed" may be varied, so that at every revolution the tool
travels from 1/64 of an inch upwards along the surface of its work.
This regularity of action adds greatly to the value of the slide-rest;
and the screw device also enables the workman to chase a thread of
absolutely constant "pitch" on a metal bar; so that a screw-cutting
lathe is not only a shaping machine but also the equivalent of a whole
armoury of stocks and dies.
Some lathes have rests which carry several tools held at different
distances from its axis, the cuts following one another deeper and
deeper into the metal in a manner exactly similar to the harvesting
of a field of corn by a succession of reaping machines. The recent
improvements in tool-steel render it possible to get a much deeper cut
than formerly, without fear of injury to the tool from overheating.
This results in a huge saving of time.
For the boring of large cylinders an upright lathe is generally used,
as the weight of the metal might cause a dangerous "sag" were the
cylinder attached horizontally by one end to a facing-plate. Huge
wheels can also be turned in this type of machine up to 20 feet or
more in diameter; and where the cross-bar carrying the tools is fitted
with several tool-boxes, two or more operations may be conducted
simultaneously, such as the turning of the flange, the boring of the
axle hole, and the facing of the rim sides.
[Illustration: A Gun Lathe. 154 feet long between centres, for boring
and turning guns which, with their mountings, weigh 165 tons when
complete. The makers are the Niles-Bement-Pond Co. of New York.]
Perhaps the most imposing of all lathes are those which handle large
cannon and propeller shafts, such as may be seen in the works of Sir
W. G. Armstrong, Whitworth, and Company; of Messrs. Vickers, Sons and
Maxim; and of other armament and shipbuilding firms. The Midvale Steel
Company have in their shops at Hamilton, Ohio, a monster boring lathe
which will take in a shaft 60 feet long, 30 inches in diameter, and
bore a hole from one end to the other 14 inches in diameter. To do
this, the lathe must attack the shaft at both ends simultaneously, as a
single boring bar of 60 feet would not be stiff enough to keep the hole
cylindrical. The shaft is placed in a revolving chuck in the central
portion of the lathe--which has a total length of over 170 feet--and
supported further by two revolving ring rests on each side towards the
extremities. With work so heavy, the feeding up of the tool to its
surface cannot be done conveniently by hand control, and the boring
bars are therefore advanced by hydraulic pressure, a very ingenious
arrangement ensuring that the pressure shall never become excessive.
Perhaps the type of lathe most interesting to the layman is the
_turret_ lathe, generally used for the manufacture of articles turned
out in great numbers. The headstock--_i.e._ the revolving part which
grips the object to be turned--is hollow, so that a rod may be passed
right through it into the vicinity of the tools, which are held in a
hexagon "turret," one tool projecting from each of its sides. When one
tool has been finished with, the workman does not have the trouble
of taking it out of the rest and putting another in its place; he
merely turns the turret round, and brings another instrument opposite
the work. If the object--say a water-cock--requires five operations
performing on it in the lathe, the corresponding tools are arranged in
their proper order round the turret. Stops are arranged so that as soon
as any tool has advanced as far as is necessary a trip-action checks
the motion of the turret, which is pulled back and given a turn to make
it ready for the next attack.
One of the advantages of the turret lathe, particularly of the
automatic form which shifts round the tool-box without human
intervention, is its power of relieving the operator of the purely
mechanical part of his work. Those who are familiar with the inside of
some of our large workshops will have noticed men and boys who make the
same thing all day and every day, and are themselves not far removed
from machines. The articles they make are generally small and very
rapidly produced, and the endless repetition of the same movements
on the part of the operator is very tedious to watch, and must be
infinitely more so to perform. Such an occupation is not elevating,
and those engaged in it cannot take much interest in their work, or
become fitted for a better position. When this work is done by an
automatic lathe the machine performs the necessary operations, and the
man supplies the intelligence, and, by exercising his thinking powers,
becomes more valuable to his employers and himself. The introduction
of new machines and methods generally has a stimulating effect on the
whole shop, whatever the Erewhonians might say. The hubs and spindles
of bicycles are cut from the solid bar by these automata; the tender
has merely to feed them with metal, and they go on smoothing, shaping,
and cutting off until the material is all used up. The existence of
such lathes largely accounts for the low price of our useful metal
steeds at the present time.
A great amount of shaping is now done by milling cutters in preference
to firmly-fixed edged tools. The cutter is a rod or disc which has its
sides, end, or circumference serrated with deep teeth, shaped to the
section of the cut needed. Revolving at a tremendous speed, it quickly
bites its way into anything it meets just so far as a stop allows it to
go.
One of the most ingenious machines to which the milling tool has been
fitted is the well-known Blanchard lathe, which copies, generally in
wood, repetitive work, such as the stocks for guns and rifles. The
lathe has two sets of centres--one for the copy, the other for the
model--parallel on the same bed, and turned at equal speeds and in
the same direction by a train of gear wheels. The milling cutter is
attached to a frame, from which a disc projects, and is pressed by a
spring against the model. As the latter revolves, its irregular shape
causes the disc, frame, and cutter to move towards or away from its
centre, and therefore towards or away from the centre of the copy,
which has all superfluities whisked off by the cutter. The frame is
gradually moved along the model, reproducing in the rough block a
section similar to the part of the model which it has reached.
The self-centring chuck is an accessory which has proved invaluable
for saving time. It may most easily be described as a circular plate
which screws on to the inner end of the mandrel (the spindle imparting
motion to the object being machined) and has in its face three slots
radiating from the centre at angles of 120°. In each slot slides a
stepped jaw, the under side of which is scored with concentric grooves
engaging with a helical scroll turned by a key and worm gear acting
on its circumference. The jaws approach or recede from the centre
symmetrically, so that if a circular object is gripped, its centre will
be in line with the axis of the lathe. Whether for gripping a tiny
drill or a large wheel, the self-centring chuck is indispensable.
PLANING-MACHINES
Not less important in engineering than the truly curved surface is the
true plane, in which, as Euclid would say, any two points being taken,
the straight line between them lies wholly in that superficies. The
lathe depends for its efficiency on the perfect flatness of all areas
which should be flat--the guides, the surface plates, the bottom and
sides of the headstock, and, above all, of the slide rest. For making
plane metal superficies, a machine must first be constructed which
itself is above suspicion; but when once built it creates machines like
itself, capable of reproducing others _ad infinitum_.
Many amateur carpenters pride themselves on the beautiful smoothness of
the boards over which they have run their jack planes. Yet, as compared
with the bed of a lathe, their best work will appear very inaccurate.
The engineer's planing-machine in no way resembles its wooden relative.
In the place of a blade projecting just a little way through a surface
which prevents it from cutting too deep into the substance over which
it is moving, we have a steel chisel very similar to the cutting tools
of a lathe attached to a frame passing up and down over a bed to which
the member holding the chisel is perfectly parallel. The article to
be planed is rigidly attached to the bed and travels with it. Between
every two strokes the tool is automatically moved sideways, so that no
two cuts shall be in the same line. After the whole surface has been
"roughed," a finishing cutter is brought in action, and the process is
repeated with the business edge of the tool rather nearer to the bed.
Joseph Clement, a contemporary of Babbage, Maudslay, and Nasmyth,
is usually regarded as the inventor of the planing-machine. By 1825
he had finished a planer, in which the tool was stationary and the
work moving under it on a rolling bed. Two cutters were attached to
the overhead cross rail, so that travel in either direction might be
utilised. The bed of the machine, on which the work was laid, passed
under the cutters on perfectly true rollers or wheels, lodged and held
in their bearings as accurately as the best mandrel could be, and
having set screws acting against their ends, totally preventing all
end-motion. The machine was bedded on a massive and solid foundation
of masonry in heavy blocks, the support at all points being so
complete as effectually to destroy all tendency to vibration, with
the object of securing full, round, and quiet cuts. The rollers on
which the planing-machine travelled were so true, that Clement himself
used to say of them, "If you were to put a paper shaving under one
of the rollers it would at once stop the rest." Nor was this an
exaggeration--the entire mechanism, notwithstanding its great size,
being as true and accurate as a watch.[6] Mr. Clement next made a
revolving attachment for the bed, in which bodies could be revolved
under the cutter, on an axis parallel to the direction of travel.
According to the wish of the operator, the object was converted into
a cylinder, cone, or prism by its movements under the planing-tool.
So efficient was the machine that it earned its maker upwards of ten
pounds a day, at the rate of about eighteen shillings a square foot,
until rivals appeared in the field and finally reduced the cost of
planing to a few pence for the same area.
There are two main patterns of planes now in general use. The first
follows the original design of Clement; the second has a fixed bed
but a moving tool. Where the work is very heavy, as in the case of
armour-plates for battleships, the power required to suddenly reverse
the motion of a vast mass of metal is enormous, many times greater
than the energy expended on the actual planing. For this reason the
moving-bed machines have had to be greatly improved; and in some cases
replaced by fixed-bed planers.
It is an impressive sight to watch one of these huge mechanisms
reducing a rough plate, weighing twenty tons or more, to a smoothness
which would shame the best billiard table. The machine, which towers
thirty feet into the air and completely dwarfs the attendant, who has
it as thoroughly under control as if it were a small file, bites great
shining strips forty feet long, maybe, off the surface of the passive
metal, and leaves a series of grooves as truly parallel as the art of
man can make them. There is no fuss, no sticking, no stop, no noise;
the force of electricity or steam, transmitted through wonderfully
cut and arranged gear-wheels, is irresistible. The tool, so hard that
a journey through many miles of steel has no appreciable effect on its
edge, shears its way remorselessly over the surface which presently may
be tempered to a toughness resembling its own. If you want to resharpen
the tool, it will be no good to attack it with any known metal. But
somewhere in the works there is a machine whose buzzing emery-wheels
are more than a match for it, and rapidly grind the blunted edge into
its former shape, so that it is ready to flay another plate, one skin
at a time.
Planing-machines are of many shapes. Some have an upright on each side
of the bed limiting the width of the work they can take; others are
open-sided, one support of extra strength replacing the two, enabling
the introduction of a plate twice as broad as the bed. Others, again,
are built on the verge of a pit, so that they may cut the edges of an
up-ended plate, and make it fit against its fellows so truly that you
could not slip a sheet of paper edgeways between them. Thus has man,
so frail and delicate in himself, shaped metal till it can torture
its kind to suit his will, which he makes known to it by opening this
valve or pulling on that lever. Not only does he flay it, but pierces
it through and through; twists it into all manner of shapes; hacks
masses off as easily as he would cut slices from a loaf; squeezes it in
terrible presses to a fraction of its original thickness; and otherwise
so treats it that we are glad that our scientific observations have as
yet discovered no sentience in the substances reduced to our service.
THE STEAM HAMMER
The Scandinavian god Thor was a marvellous blacksmith. Thursday
should remind us weekly of Odin's son, from whose hammer flashed the
lightning; and, through him, of Vulcan, toiling at his smithy in the
crater of Vesuvius. In spite of the pictures drawn for us by pagan
mythologists of their god-smiths, we are left with the doubt whether
these beings, if materialised, might not themselves be somewhat alarmed
by the steam hammer which mere mortals wield so easily.
The forge is without dispute the "show-place" of a big factory, where
huge blocks of metal feel the heavy hand of steam. As children we
watched the blacksmith at his anvil, attracted and yet half-terrified
by the spark-showers flying from a white-hot horseshoe. And even
the adult, long used to startling sights, might well be fascinated
and dismayed by the terrific blows dealt on glowing ingots by the
mechanical sledge.
[Illustration: A steam hammer at work in Woolwich Arsenal, forging
a steel ingot for the inner tube of a big gun. It delivers a blow
equivalent to the momentum of a falling mass weighing 4000 tons. As
speech is inaudible, the foreman gives hand signals to direct his men,
who wear large canvas fingerless gloves to protect their hands from the
intense heat.]
James Nasmyth, the inventor of this useful machine, was the son of a
landscape painter, who from his earliest youth had taken great interest
in scientific and mechanical subjects of all kinds. At fifteen he made
a steam-engine to grind his father's paints, and five years later a
steam carriage "that ran many a mile with eight persons on it. After
keeping it in action two months," he says in an account of his early
life, "to the satisfaction of all who were interested in it, my friends
allowed me to dispose of it, and I sold it--a great bargain--after
which the engine was used in driving a small factory. I may mention
that in that engine I employed the waste steam to cause an increased
draught by its discharge up the chimney. This important use of waste
steam had been introduced by George Stephenson some years before,
though entirely unknown to me."
This interesting peep at the infancy of the motor carriage reveals
mechanical capabilities of no mean order in young James. He soon
entered the service of Mr. Joshua Field, Henry Maudslay's partner, and
in 1834 set up a business on his own account at Manchester.
At this date the nearest approach to the modern steam hammer was the
"tilt" hammer, operated by horse-, water-, or steam-power. It resembled
an ordinary hand hammer on a very large scale, but as it could be
raised only a small distance above its anvil, it became less effective
as the size of the work increased, owing to the fall being "gagged."
In 1837 Mr. Nasmyth interviewed the directors of the Great Western
Steamship Company with regard to the manufacture of some unusually
powerful tools which they needed for forging the paddle-shaft of the
_Great Britain_. As the invention of the steam-engine had demanded the
improvement of turning methods, so now the increase in the size of
steamboats showed the insufficiency of forging machinery.
Mr. Nasmyth put on his thinking-cap. Evidently the thing needed was a
method for raising a very heavy mass of metal easily to a good height,
so that its great weight might fall with crushing force on the object
between it and the anvil. How to raise it? Brilliant idea! Steam! In a
moment Nasmyth had mentally pictured an inverted steam cylinder rested
on a solid upright overhanging the anvil and a block of iron attached
to its piston-rod. All that would then be necessary was to admit steam
to the under side of the piston until the block had risen to its full
height, and to suddenly open a valve which would cut off the steam
supply and allow the vapour already in the cylinder to escape.
By the next post he sent a sketch to the company, who approved his
design heartily, but were unable to use it, since the need for the
paddle-shaft had already been nullified by the substitution of a screw
as the motive power of their ship. Poor Nasmyth knew that he had
discovered a "good thing," but British forge-masters, with a want of
originality that amounted to sheer blind stupidity, refused to look
at the innovation. "We have not orders enough to keep in work the
forge-hammers we have," they wrote, "and we don't want any new ones,
however improved they may be."
His invention, therefore, appeared doomed to failure. Help, however,
came from France in the person of Mr. Schneider, founder of the famous
Creusot Iron Works, notorious afterwards as the birthplace of the Boer
"Long Toms." Mr. Nasmyth happened to be away when Mr. Schneider and a
friend called at the Manchester works, but his partner, Mr. Gaskell,
showed the French visitors round the works, and also told them of
the proposed steam hammer. The designs were brought out, so that its
details might be clearly explained.
Years afterwards Nasmyth returned the visit, and saw in the Creusot
Works a crank-shaft so large that he asked how it had been forged. "By
means of your steam hammer," came the reply. You may imagine Nasmyth's
surprise on finding the very machine at work in France which his own
countrymen had so despised, and his delight over its obvious success.
On returning home he at once raised money enough to secure a patent,
protected his invention, and began to manufacture what has been
described as "one of the most perfect of artificial machines and
noblest triumphs of mind over matter that modern English engineers
have developed." A few weeks saw the first--a 30-cwt.--hammer at work.
People flocked to watch its precision, its beauty of action, and the
completeness of control which could arrest it at any point of its
descent so instantaneously as to crack without smashing a nut laid
on the anvil. "Its advantages were so obvious that its adoption soon
became general, and in the course of a few years Nasmyth steam hammers
were to be found in every well-appointed workshop both at home and
abroad."[7]
Nasmyth's invention was improved upon in 1853 by Mr. Robert Wilson, his
partner and successor. He added an automatic arrangement which raised
the "tup," or head, automatically from the metal it struck, so that
time was saved and loss of heat to the ingot was also avoided. The
beauty of the "balance valve," as it was called, will be more clearly
understood if we remember that the travel of the hammer is constantly
increasing as the piece on the anvil becomes thinner under successive
blows. Under the influence of this very ingenious valve every variety
of blow could be dealt. By simply altering the position of a tappet
lever by means of two screws, a blow of the exact force required could
be repeated an indefinite number of times. "It became a favourite
amusement to place a wine-glass containing an egg upon the anvil, and
let the block descend upon it with its quick motion; and so nice was
its adjustment, and so delicate its mechanism, that the great block,
weighing perhaps several tons, could be heard playing tap, tap upon the
egg without even cracking the shell, when, at a signal given to the man
in charge, down would come the great mass, and the egg and glass would
be apparently, as Walter Savage Landor has it, 'blasted into space.'"[8]
Later on Mr. Wilson added an equally important feature in the shape of
a double-action hand-gear, which caused the steam to act on the top as
well as the bottom of the piston, thus more than doubling the effect of
the hammer.
The largest hammer ever made was that erected by the Bethlehem Iron
Company of Pennsylvania. The "tup" weighed 125 tons. After being in use
for three years the owners consigned it to the scrap-heap, as inferior
to the hydraulic press for the manufacture of armour-plate, though it
had cost them £50,000. They then erected in its stead, for an equal sum
of money, a 14,000-ton pressure hydraulic press, which fitly succeeds
it as the most powerful of its kind in the world.
The change was made for three reasons. First, that the impact of so
huge a block of metal necessitates the anvil being many times as heavy,
and even then the shock to surrounding machinery may be very severe.
Secondly, the larger the forging to be hammered, the less is the
reaction of the anvil, so that all the force of the blow tends to be
absorbed by the side facing the hammer; whereas with a small bar the
anvil's inertia would have almost as much effect as the actual blow.
Thirdly, the blow of the hammer is so instantaneous that the metal has
not time to "flow" properly, and this leads to imperfect forgings, the
surface of which may have been cracked. For very large work, therefore,
the hammer is going out of fashion and the press coming in, though for
lighter jobs it is still widely used.
Before leaving the subject we may glance at the double-headed
horizontal hammer, such as is to be found in the forge-shop of the
Horwich Railway Works. Two hammers, carried on rails and rollers,
advance in unison from each side and pound work laid on a support
between them. Each acts as anvil to the other, while doing its full
share of the work. So that not only is a great deal of weight saved,
but shocks are almost entirely absorbed; while the fact that each
hammer need make a blow of only half the length of what would be
required from a single hammer, enables twice as many blows to be
delivered in a given time.
HYDRAULIC TOOLS
Before discussing these in detail we shall do well to trace the history
of the Bramah press, which may be said to be their parent, since the
principle employed in most hydraulic devices for the workshop, as
also the idea of using water as a means of transmitting power under
pressure, are justly attributed to Joseph Bramah.
If you take a dive into the sea and fall flat on the surface instead
of entering at the graceful angle you intended, you will feel for some
time afterwards as if an enemy had slapped you violently on the chest
and stomach. You have learnt by sad experience that water, which seems
to offer so little resistance to a body drawn slowly through it, is
remarkably hard if struck violently. In fact, if enclosed, it becomes
more incompressible than steel, without in any way losing its fluidity.
We possess in water, therefore, a very useful agent for transmitting
energy from one point to another. Shove one end of a column of water,
and it gives a push to anything at its other end; but then it must be
enclosed in a tube to guide its operation.
By a natural law all fluids press evenly on every unit of a surface
that confines them. You may put sand into a bucket with a bottom of
cardboard and beat hard upon the surface of the sand without knocking
out the bottom. The friction between the sand particles and the
bucket's sides entirely absorbs the blow. But if water were substituted
for sand and struck with an object that just fitted the bucket so as
to prevent the escape of liquid, the bottom, and sides, too, would be
ripped open. The writer of this book once fired a candle out of a gun
at a hermetically sealed tin of water to see what the effect would be.
(Another candle had already been fired through an iron plate 1/4 of an
inch thick.) The impact _slightly_ compressed the water in the tin,
which gave back all the energy in a recoil which split the sheet metal
open and flung portions of it many feet into the air. But the candle
never got through the side.
This affords a very good idea of the almost absolute incompressibility
of a liquid.
We may now return to history. Joseph Bramah was born in 1748 at
Barnsley, in Yorkshire. As the son of a farm labourer his lot in life
would probably have been to follow the plough had not an accident to
his right ankle compelled him to earn his living in some other way. He
therefore turned carpenter and developed such an aptitude for mechanics
that we find him, when forty years old, manufacturing the locks with
which his name is associated, and six years later experimenting with
the hydraulic press. This may be described simply as a large cylinder
in which works a solid piston of a diameter almost equal to that of
the bore, connected to a force pump. Every stroke of the pump drives a
little water into the cylinder, and as the water pressure is the same
throughout, the total stress on the piston end is equal to that on the
pump plunger multiplied by the number of times that the one exceeds the
other in area. Suppose, then, that the plunger is one inch in diameter
and the piston one foot, and that a man drives down the plunger with a
force of 1,000 lbs., then the total pressure on the piston end will be
144 × 1,000 lbs.; but for every inch that the plunger has travelled the
piston moves only 1/144 of an inch, thus illustrating the law that what
is gained in time is lost in power, and _vice versâ_.
The great difficulty encountered by Bramah was the prevention of
leakage between the piston and the cylinder walls. If he packed
it so tightly that no water could pass, then the piston jammed;
if the packing was eased, then the leak recommenced. Bramah tried
all manner of expedients without success. At last his foreman,
Henry Maudslay--already mentioned in connection with the lathe
slide-rest--conceived an idea which showed real genius by reason of
its very simplicity. Why not, he said, let the water itself give
sufficient tightness to the packing, which must be a collar of stout
leather with an inverted U-shaped section? This suggestion saved the
situation. A recess was turned in the neck of the cylinder at the point
formerly occupied by the stuffing-box, and into this the collar was
set, the edges pointing downwards. When water entered under pressure
it forced the edges in different directions, one against the piston,
the other against the wall of the recess, with a degree of tightness
proportioned to the pressure. As soon as the pressure was removed the
collar collapsed, and allowed the piston to pass back into the cylinder
without friction. A similar device, to turn to smaller things for a
moment, is employed in a cycle tyre inflater, a cup-shaped leather
being attached to the rear end of the piston to seal it during the
pressure stroke, though acting as an inlet valve for the suction stroke.
What we owe to Joseph Bramah and Henry Maudslay for their joint
invention--the honour must be divided, like that of designing the
steam hammer between Nasmyth and Wilson--it would indeed be hard to
estimate. Wherever steady but enormous effort is required for lifting
huge girders, houses, ships; for forcing wheels off their axles; for
elevators; for advancing the boring shield of a tunnel; for compressing
hay, wool, cotton, wood, even metal; for riveting, bending, drilling
steel plates--there you will find some modification of the hydraulic
press useful, if not indispensable.
However, as we are now prepared for a consideration of details, we may
return to our workshop, and see what water is doing there. Outside
stands a cylindrical object many feet broad and high, which can move up
and down in vertical guides. If you peep underneath, you notice the
shining steel shaft which supports the entire weight of this tank or
coffer filled with heavy articles--stones, scrap iron, etc. The shaft
is the piston-plunger of a very long cylinder connected by pipes to
pumping engines and hydraulic machines. It and the mass it bears up
serves as a reservoir of energy. If the pumping engines were coupled up
directly to the hydraulic tools, whenever a workman desired to use a
press, drill, or stamp, as the case might be, he would have to send a
signal to the engine-man to start the pumps, and another signal to tell
him when to stop. This would lead to great waste of time, and a danger
of injuring the tackle from over driving. But with an accumulator there
is always a supply of water under pressure at command, for as soon as
the ram is nearly down, the engines are automatically started to pump
it up again. In short, the accumulator is to hydraulic machinery what
their bag is to bagpipes, or the air reservoir to an organ.
In large towns high-pressure water is distributed through special mains
by companies who make a business of supplying factories, engineering
works, and other places where there is need for it, though not
sufficient need to justify the occupiers in laying down special pumping
plant. London can boast five central distributing stations, where
engines of 6,500 h.p. are engaged in keeping nine large accumulators
full to feed 120 miles of pipes varying in diameter from seven inches
downwards. The pressure is 700 lbs. to the square inch. Liverpool
has twenty-three miles of pipes under 850 lbs. pressure; Manchester
seventeen miles under 1,100 lbs. To these may be added Glasgow, Hull,
Birmingham, Geneva, Paris, Berlin, Antwerp, and many other large cities
in both Europe and the United States.
For very special purposes, such as making metal forgings, pressures
up to _twelve tons_ to the square inch may be required. To produce
this "intensifiers" are used, _i.e._ presses worked from the ordinary
hydraulic mains which pump water into a cylinder of larger diameter
connected with the forging press.
The largest English forging press is to be found in the Openshaw
Works of Sir W. G. Armstrong, Whitworth, and Company. Its duty is to
consolidate armour-plate ingots by squeezing, preparatory to their
passing through the rolling mills. It has one huge ram 78 inches in
diameter, into the cylinder of which water is pumped by engines of
4,000 h.p., under a pressure of 6,720 lbs. to the square inch, which
gives a total ram force of 12,000 tons. It has a total height of 33
feet, is 22 feet wide, and 175 feet long, and weighs 1,280 tons. On
each side of the anvil is a trench fitted with platforms and machinery
for moving the ingot across the ingot block. Two 100-ton electric
cranes with hydraulic lifting cylinders serve the press.
[Illustration: A HUGE HYDRAULIC PRESS
The 12,000-ton pressure Whitworth Hydraulic Press, used for
consolidating steel ingots for armour-plating. Water is forced into the
ram cylinder at a pressure of three tons to the square inch. Notice the
man to the left of the press.]
The Bethlehem Works "squeezer" has two rams, each of much smaller
diameter than the Armstrong-Whitworth, but operated by a 10-1/2 tons
pressure to the square inch. It handles ingots of over 120 tons weight
for armour-plating. In 1895 Mr. William Corey, of Pittsburg, took
out a patent for toughening nickel steel plates by subjecting them,
while heated to a temperature of 2,000° F., to great compression,
which elongates them only slightly, though reducing their thickness
considerably. The heating of a large plate takes from ten to twenty
hours; it is then ready to be placed between the jaws of the big press,
which are about a foot wide. The plate is moved forward between the
jaws after each stroke until the entire surface has been treated. At
one stroke a 17-inch plate is reduced to 16 inches, and subsequent
squeezings give it a final thickness of 14 inches. Its length has
meanwhile increased from 16 to 18-1/2 feet, or in that proportion,
while its breadth has remained practically unaltered. A simple sum
shows that metal which originally occupied 32-2/3 cubic inches has now
been compressed into 31 cubic inches. This alteration being effected
without any injury to the surface, a plate very tough inside and very
hard outside is made. The plate is next reheated to 1,350° F., and
allowed to cool very gradually to a low temperature to "anneal" it.
Then once again the furnaces are started to bring it back to 1,350°,
when cold water is squirted all over the surface to give it a proper
temper. If it bends and warps at all during this process, a slight
reheating and a second treatment in the press restores its shape.
The hydraulic press is also used for bending or stamping plates in all
manners of forms. You may see 8-inch steel slabs being quietly squeezed
in a pair of huge dies till they have attained a semicircular shape,
to fit them for the protection of a man-of-war's big-gun turret; or
thinner stuff having its ends turned over to make a flange; or still
slenderer metal stamped into the shape of a complete steel boat, as
easily as the tinsmith stamps tartlet moulds. In another workshop a
pair of massive jaws worked by water power are breaking up iron pigs
into pieces suitable for the melting furnace.
The manufacture of munitions of war also calls for the aid of this
powerful ally. Take the field-gun and its ammunition. "The gun itself
is a steel barrel, hydraulically forged, and afterwards wire-wound; the
carriage is built up of steel plates, flanged and shaped in hydraulic
presses; the wheels have their naves composed of hydraulically flanged
and corrugated steel discs, and even the tyres are forced on cold
by hydraulic tyre-setters, the rams of which are powerful enough to
reduce the diameter of the welded tyre until the latter tightly nips
the wheel. The shells for the gun are punched and drawn by powerful
hydraulic presses, and the copper driving-bands are fixed on the
projectiles in special hydraulic presses. Quick-firing cartridge-cases
are capped, drawn, and headed by an hydraulic press, whose huge mass
always impresses the uninitiated as absurdly out of proportion to the
small size of the finished case, and finally the cordite firing charge
is dependent on hydraulic presses for its density and shape."[9]
The press for placing the "driving-band" on a shell is particularly
interesting. After the shell has been shaped and its exterior turned
smooth and true, a groove is cut round it near the rear end. Into
this groove a band of copper is forced to prevent the leakage of gas
from the firing charge past the shell, and also to bite the rifling
which imparts a rotatory motion to the shell. The press for performing
the operation has six cylinders and rams arranged spoke-wise inside
a massive steel ring; the rams carrying concave heads which, when
the full stroke is made, meet at the centre so as to form a complete
circle. "Pressure is admitted," says Mr. Petch, "to the cylinders by
copper pipes connected up to a circular distributing pipe. The press
takes water from the 700-pounds main for the first 3/8-inch of the
stroke, and for the last 1/8-inch water pressure at 3 tons per square
inch is used. The total pressure on all the rams to band a 6-inch shell
is only 600 tons, but for a 12-inch shell no less than 2,800 tons is
necessary."
ELECTRIC TOOLS IN A SHIPYARD
Of late years electricity has taken a very prominent part in workshop
equipment, on account of the ease with which it can be applied to a
machine, the freedom from belting and overhead gear which it gives, and
its greater economy. In a lathe-shop, where only half the lathes may be
in motion at a time, the shafting and the belts for the total number is
constantly whirling, absorbing uselessly a lot of power. If, however,
a separate motor be fitted to each lathe, the workman can switch it on
and off at his pleasure.
The New York Shipbuilding Company, a very modern enterprise, depends
mainly on electrical power for driving its machinery, in preference to
belting, compressed air, or water. Let us stroll through the various
shops, and note the uses to which the current has been harnessed.
Before entering, our attention is arrested by a huge gantry crane,
borne by two columns which travel on rails. From the cross girder,
or bridge, 88 feet long, hang two lifting magnets, worked by 25 h.p.
motors, which raise the load at the rate of 20 feet per minute. Motors
of equal power move the whole gantry along its rails over the great
piles of steel plates and girders from which it selects victims to feed
the maw of the shops.
The main building is of enormous size, covering with its single roof no
less than eighteen acres! Just imagine four acres of skylights and two
acres of windows, and you may be able to calculate the little glazier's
bill that might result from a bad hailstorm. In this immense chamber
are included the machine, boiler, blacksmith, plate, frame, pipe, and
mould shops, the general storerooms, the building ways, and outfitting
slips. "The material which enters the plate and storage rooms at one
end, does not leave the building until it goes out as a part of the
completed ship for which it was intended, when the vessel is ready to
enter service; there are installed in one main building, and under one
roof, all the material and machinery necessary for the construction of
the largest ship known to commerce, and eight sets of ship-ways, built
upon masonry foundations, covered by roofs of steel and glass, and
spanned by cranes up to 100 tons lifting capacity, are practically as
much a part of the immense main building as the boiler shop or machine
shop."[10]
A huge 100-ton crane of 121-foot span dominates the machine-shop and
ship-ways at a height of 120 feet. It toys with a big engine or boiler,
picking it up when the riveters, caulkers, and fitters have done their
work, and dropping it gently into the bowels of a partly-finished
vessel. A number of smaller cranes run about with their loads. Those
which handle plates are, like the big gantry already referred to,
equipped with powerful electro-magnets which fix like leeches on the
metal, and will not let go their hold until the current is broken by
the pressing of a button somewhere on the bridge. Sometimes several
plates are picked up at once, and then it is pretty to see how the man
in charge drops them in succession, one here, another there, by merely
opening and closing the switch very quickly, so that the plate furthest
from the magnets falls before the magnetism has passed out of the
nearer plates.
Another interesting type is the extension-arm crane, which shoots out
an arm between two pillars, grips something, and pulls it back into the
main aisle, down which it travels without impediment.
On every side are fresh wonders. Here is an immense rolling machine,
fed with plates 27 feet wide, which bends the 1-1/8-inch thick metal
as if it were so much pastry; or turns over the edges neatly at the
command of a 50 h.p. motor. There we have an electric plate-planer
scraping the surface of a sheet half the length of a cricket pitch. As
soon as a stroke is finished the bed reverses automatically, while the
tool turns over to offer its edge to the metal approaching from the
other side. All so quietly, yet irresistibly done!
Now mark these punches as they bite 1-1/4-inch holes through steel
plates over an inch thick, one every two seconds. A man cutting wads
out of cardboard could hardly perform his work so quickly and well.
Almost as horribly resistless is the circular saw which eats its way
quite unconcernedly through bars six inches square, or snips lengths
off steel beams.
What is that strange-looking machine over there? It has three columns
which move on circular rails round a table in the centre. Up and down
each column passes a stage carrying with it a workman and an electric
drill working four spindles. Look! here comes a crane with a boiler
shell, the plates of which have been bolted in position. The crane lets
down its load, end-up, on to the table, and trots off, while the three
workmen move their columns round till the twelve drills are opposite
their work. Then whirr! a dozen twisted steel points, ranged in three
sets of four, one drill above the other, bite into the boiler plates,
opening out holes at mathematically correct intervals all down the
overlapping seam-plates. This job done, the columns move round the
boiler, and their drills pierce it first near the lower edge, then near
the upper. The crane returns, grips the cylinder, and bears it off to
the riveters, who are waiting with their hydraulic presses to squeeze
the rivets into the holes just made, and shape their heads into neat
hemispheres. As it swings through the air the size of the boiler is
dwarfed by its surroundings; but if you had put a rule to it on the
table you would have found that it measured 20 feet in diameter and as
many in length. A few months hence furnaces will rage in its stomach,
and cause it to force tons of steam into the mighty cylinders driving
some majestic vessel across the Atlantic.
We pass giant lathes busy on the propeller shafts, huge boring mills
which slowly smooth the interior of a cylinder, planers which face the
valve slides; and we arrive, eye-weary, at the launching-ways where
an ocean liner is being given her finishing touches. Then we begin
to moralise. That 600-foot floating palace is a concretion of parts,
shaped, punched, cut, planed, bored, fixed by electricity. Where does
man come in? Well, he harnessed the current, he guided it, he said "Do
this," and it did it. Does not that seem to be his fair share of the
work?
FOOTNOTES:
[5] _Industrial Biographies_, Dr. S. Smiles.
[6] _Industrial Biographies._
[7] _Industrial Biographies._
[8] _Chambers's Encyclopædia._
[9] Mr. A. F. Petch in _Cassier's Magazine_.
[10] _Cassier's Magazine._