MACHINES FOR MAKING MACHINES
WHILE we may glory in the wonderful mechanical progress of to-day, we
must not overlook the marvelous skill of the ancient artisan nor forget
that it is to his inventive genius that we are indebted for practically
every hand tool we possess. Only a few special tools owe their origin
to the modern inventor. All the rest date back beyond the twilight of
history. We have merely improved upon these tools by slight changes of
design or the employment of better materials in their construction.
As users of these tools we cannot begin to compare with the skilled
workman of ancient days. Our progress is shown not in the _development_
of skill, but in the _loss_ of it. We have taken the tool out of the
human hand and put it into an inanimate machine. It is only very
recently that the tool was delivered to the machine and that act marked
the dawn of the present remarkable mechanical era.
Machines for making machines date back to the time of the early
Egyptians. They had their pole lathes and bow drills, but these
machines only partially relieved the workman of his labors, and the
quality of the work still depended upon a degree of skill that was
acquired only through years of patient apprenticeship.
The pole lathe, by the way, consisted merely of a pair of centers
between which the work was mounted, a pole attached to the ceiling
and a strap or rope passed around the work and fastened at one end to
a pole and at the other to a pedal resting against the floor. (See
Figure 24.) When the pedal was depressed, the strap was pulled down
and the work was revolved. On releasing the pedal, the spring of
the pole pulled the strap up and reversed the rotation of the work.
Thus by alternately depressing and releasing the pedal, the work was
intermittently revolved against a chisel which was rested on a block
and guided by the workman. Small work could be turned out on such a
lathe with considerable precision, but when it came to large parts,
particularly parts of steel, the workman was easily tired by the effort
of operating the pedal and was apt to be irregular in the guiding of
the tool.
[Illustration: FIG. 24.--PRIMITIVE POLE LATHE]
Up to the middle of the eighteenth century practically no advance had
been made over the ancient lathe of the Egyptians, and when, 150 years
ago, the steam engine was invented the task of building the engine
seemed almost insuperable.
James Watt was a maker of mathematical instruments, a man of great
skill and precision as a craftsman, but he dealt with parts of small
dimensions. When he conceived of his steam engine, he mentally pictured
the various parts as turned out with all the accuracy and finish that
was possible in the diminutive members of a scientific instrument. To
him it seemed perfectly feasible to turn a cylinder which would be
practically perfect in contour, and to fit it with a piston around
which no steam could leak. With the lathe then in existence such a fit
was easily possible on small work. But when he undertook to have the
cylinder of his engine bored, he discovered that there was no machine
that could begin to do the work properly. In fact, when Smeaton, who
was a prominent engineer of that time, investigated Watt’s steam
engine, he declared that it was such a complicated piece of work that
neither tools nor workmen existed that could build it. In Watt’s first
engine, the cylinder was only six inches in diameter and two feet long,
and a special type of boring machine was devised to bore the forged
cylinders. But the boring was so irregular that when the piston was
inserted and the steam was turned on, nothing would stop the flow of
steam that leaked around the piston. In vain did James Watt use cork,
oiled rags, tow, paper, and even old hats to stop the leakage. However,
the boring machine was improved and later a cylinder, eighteen inches
in diameter, was bored with such accuracy that the large diameter
exceeded the small diameter in the worst place by only ⅜ of an inch.
This Watt considered a very good bit of turning. To-day cylinders of
that size that vary from true by half the thickness of the paper that
this is printed on would be thrown out as defective.
It was in 1769 that Watt invented the steam engine, but that great
event did not mark the dawn of the present era of machinery. For a
quarter of a century thereafter there was little progress in the
development of machine tools. A boring machine was built that did
fair work. There were a few sawmills in which wind power was employed
to drive the saw. But lathes were still driven by foot power and the
cutting tool was still held and guided by hand.
MAUDSLEY’S “GO-CART”
The real father of the present era was a very clever British mechanical
engineer, Henry Maudsley, who undertook to eliminate the uncertainties
of the human hand by clamping the cutting tool of the lathe in a rest
and arranging the rest to slide along the length of the lathe or
transversely toward or away from the center. These two motions made it
possible to accomplish all that the workman could accomplish by hand
and at the same time the tool was held so firmly that accuracy and
precision of turning was assured. Furthermore, he provided this slide
rest with a nut that engaged a screw driven through suitable gearing
by the lathe spindle. Then, as the work revolved, the slide rest
was compelled to move along the bed of the lathe at a uniform rate.
By varying the gearing, the speed of the slide rest and the tool it
carried could be varied at will, thus making it possible to cut screw
threads of any pitch desired with a degree of accuracy unattainable by
hand.
Remarkable as was this improvement, it met with the usual opposition
that every real advance in machinery received in those days. People
referred to the slide rest as Maudsley’s “go-cart,” but it proved such
an important element of the lathe and so very valuable that before
long it was universally adopted. From that time on the skill of the
workman began to lose its importance. The man began to give way to the
machine. Precision was possible in large as well as small work. The
human element was also dispensed with in the driving of the lathe. The
foot pedal was superseded by the steam engine, and the machine came to
be known as the engine lathe.
There are many ways of working metals now in common use. Metals may be
cast in a molten state, or they may be pressed and molded into shape in
a cold state, or they may be hammered either cold or hot, but in nearly
all cases in which metal is removed in order to form a piece of work,
the chisel is used as a cutting instrument. This is perfectly apparent
in lathes and planers, but not quite so apparent in sawing, drilling,
filing, and grinding. A drill is merely a spiral chisel which revolves
upon its own center. A saw is a gang of tiny chisels, and a file
consists of still smaller chisels which are broader than those of the
saw. In grinding we have rough surfaces in which particles of emery or
carborundum act as tiny chisels. The shears, the punch, and the cutting
torch are practically the only exceptions to the rule that metals
are always cut by chisels, and even the shears may be conceived as
consisting of a pair of broad coacting chisels, while it takes little
imagination to see a form of chisel in the punch. The cutting torch is,
of course, in no sense a chisel.
In the cutting of metals the work may move against a fixed tool or the
tool may move against a fixed piece of work. In a lathe, it is the work
that revolves or rotates against the tool. In the drill and the milling
machine the tool revolves against the work.
In the planer, the tool is fixed and the work slides against it. The
shaper reverses the operation; the work is fixed and the tool moves in
a rectilinear direction.
Up to the nineteenth century practically the only machines for
cutting metals were the lathe and a crude form of boring machine.
The machinists of that day had not reached the stage where they were
able to produce anything but round work on a machine. The planer had
not been born. It was for this reason that Watt had a great deal of
difficulty in getting rectilinear motion for the piston of his engine.
He had to invent a complicated system of links and levers in order to
obtain a practically parallel motion to guide his piston in and out
of the cylinder. When the planer was invented and it was possible to
produce straight surfaces with a considerable degree of accuracy, all
of Watt’s ingenious parallel motions, went into the discard and the
cross-head and guides took their place.
It was not until long after the planer had been invented that Eli
Whitney, the American genius of cotton-gin fame, conceived the milling
machine. He reversed the operation of the lathe by placing the cutting
tool on the revolving spindle and sliding the work against it. Milling
cutters consist of wheels formed with a number of cutting edges or
chisels which are arranged either on the periphery of the wheel or on
the face of the wheel.
Following the milling machine, came the grinder, in which a revolving
wheel of an abrasive material served to wear away the surface of a
piece of work, and with this form of machine steels of great hardness
could be finished with accuracy and a high polish.
THE INTERCHANGEABLE SYSTEM
The most notable advance in machine work came early in the nineteenth
century, when what was known as the “American System” of manufacture,
or the interchangeable system, was introduced. As long as mechanics
were obliged to perform their operations largely by hand, it was
impossible to attain great accuracy. Each workman put his own
individuality into the work. As a consequence, no two pieces were of
exactly the same size or shape. This was true even with the early
power-driven machine tools. The parts might be very close to the same
size, but careful measurements showed that they varied by a minute
fraction of an inch. Hence, when a machine was assembled the unyielding
metal parts had to be filed and trimmed and hammered to fit them
together. If any accident occurred to a machine, the damaged part
could not be replaced by another taken from stock. The entire machine
had to go back to the shop where an experienced mechanic would make a
new part to replace the damaged one. In those days a machine was not
manufactured but was built as an individual mechanism, just as a house
or a boat is built to-day.
With the advent of accurate machine tools came the idea of
standardizing the parts so that hundreds and thousands of pieces could
be made of exactly the same dimensions, and in assembling a machine
the parts could be picked at random from the stock and put together
without the use of special tools and without requiring any special
fitting. This was of special importance in the tools of warfare,
because armies need quantity production, i. e., rifles, cannon, etc.
More machines of the same kind were required for an army than for any
other organization or line of work. At the close of the Napoleonic
War the British Government had 200,000 parts of muskets either partly
finished or waiting repairs. Their muskets were made after the old
system. Each one was built separately with its parts individually
fitted together, so that whenever any part was injured, the musket had
to be laid aside and sent back to the workshop for repairs.
Long before that time, the idea of making standard guns had been hit
upon in France. Thomas Jefferson, while Minister to France, in 1785,
wrote of the French system which was then being developed by a mechanic
named Le Blanc. He was building a musket in which the parts were
of standard pattern, and which could be assembled by taking pieces
haphazard as they came to hand and putting them together without
special fitting. Thomas Jefferson called the attention of the American
Government to this system and showed that it was possible to produce
muskets cheaper by that method of manufacture. However, our Government
at that time failed to avail itself of the opportunity of utilizing
this system of manufacture.
Later on, the idea was taken up in this country by Eli Whitney and by
Simeon North. When Whitney attempted to introduce the system, he was
laughed at by French and English ordnance officials, and even our own
Government officials were skeptical, particularly when they found that
it required so much preparation in the way of machinery and designing
of parts before a single musket was completed. It seemed like a waste
of money to invest in so much preparation. But Whitney was soon able
to silence all his critics by taking to Washington ten pieces of each
part of a musket and then selecting at hazard from each pile of pieces
the requisite parts and putting together ten muskets. It was not long
before the foreign governments saw the importance of this method of
manufacture. Great Britain later adopted it in the making of her own
rifles and called the process the “American System.”
But it was not only in the field of rifles that interchangeable
manufacture made itself felt. The New England clock industry provides
an interesting illustration. At first the clocks were made of wood,
but early in the nineteenth century, a clock maker, Chauncey Jerome
by name, designed a brass clock in which the parts were made on the
interchangeable system. Instead of building each clock as a separate
piece of work, clocks were turned out by the thousands, and at an
extremely low price. Soon he had flooded this country with his clocks
and began to look around for other markets. Machinery had been used by
other clock makers in producing wooden clocks, and movements which had
cost $50 each in 1840 had been reduced to $5. But Chauncey Jerome’s
clock was made of brass and by means of the interchangeable system of
manufacture he could produce it for less than 50 cents. The clock was
such a success in this country that Jerome decided to try it abroad.
Consequently he made arrangements with an agent in England and shipped
over a large consignment. The British Government was astonished at the
low price of the clock and was convinced that it had been undervalued.
At that time, they had a simple and ingenious method of punishing a
consigner who undervalued the goods he wished to introduce into the
country. This consisted in promptly appropriating the property at the
price given in the invoice. In due course of time, much to Jerome’s
astonishment, he received a letter from the British Government stating
that his clocks had been confiscated, and with the letter came a check
paying for them at the invoice price. Jerome was not in the least
dejected by the rebuke; on the contrary, he was rather elated, for, as
far as he could figure it out, he had a spot-cash buyer for his goods
and no selling expenses. He did not mind at all letting the British
Government have the clocks at the invoice price. So he decided to try
again with a larger shipment. To his great delight this shipment met
the same fate as the first, and in due course another good British
check arrived. Thus encouraged, Jerome sent over a third and still
larger shipment, but by that time Johnny Bull began to suspect that the
Yankee clock maker was getting the best of the bargain and, finally
convinced that clocks really could be produced with profit at the
low invoice price, he permitted them to enter his country. With this
striking example, the fame of the Yankee system of manufacture spread
over the world.
In order to have two parts alike, they must be placed under a machine
in exactly the same way. In other words, they must be set in “jigs” or
frames which are fitted into the machine in such a way that the tools
will approach the work from exactly the same angle or penetrate the
work to exactly the same depth in ten, or a hundred, or a thousand,
or a million pieces, as the case may be. Making jigs and dies consumes
a great deal of time in preparation work, but once the preparation
stage has been passed, articles are produced with wonderful rapidity
and very little waste of time. Formerly it was necessary to determine
the location of each hole in a casting separately and spend precious
time in adjusting the work to the proper position under the tool. If
the hole was to be threaded, it had to pass through several separate
operations.
THE TURRET LATHE
After the slide rest invented by Maudsley, the next great improvement
on the lathe was a turret head or a sort of turntable which carried
a number of tools. The tools are arranged to come automatically into
play one after the other. One tool, for instance, may cut a groove in
the work, another finish the face of the work, another bore a hole in
the piece and another tap the hole. In many cases, several of these
operations are performed simultaneously. The head of the lathe is
provided with a hollow spindle so that the work is automatically fed to
the tools through this spindle, and as soon as one piece is finished,
it is automatically cut off and the jaws of the clutch which holds
the work, or stock as it is called, open automatically so that a new
length may slide forward and be operated upon by the tools. The machine
requires no attention once the tools have been set up to the proper
angle, except that it must be kept supplied with bars of stock as they
are consumed, and with a copious flow of lubricant on the tools. One
operator can therefore take charge of a number of automatic lathes.
All he does is to feed them; they do the rest.
The modern drill has also gone through a great many developments in
order to speed up the work that it performs. When a casting is to have
forty or fifty holes drilled and tapped in it, instead of following the
old method of drilling each hole separately, a lot of separate drilling
spindles are used, each fitted with a drill, and these are brought
simultaneously into play. As many as fifty or sixty holes may be
drilled at a single operation, and after the holes have been drilled,
the drilling spindles move to one side to make way for the taps, which
thread such of the holes as are to receive screws. By first setting the
spindles in the proper position and then using jigs to locate the work
properly under them, the assurance is had that every one of the scores
of holes drilled will be accurately spaced apart and the spacing in
every casting will be identical.
The multiple tool system is also used in milling machines in which a
number of milling cutters either of the face or the end type come into
play simultaneously upon a piece of work set in a suitable jig, and cut
the piece with absolute precision, so that all castings will have faces
accurately spaced apart and cut to exactly the same level.
It is by such methods as these that we are able to produce such large
quantities of machinery at remarkably low cost. One of the most
notable examples of such work was the development of the Liberty
engine during the World War. This engine did not differ in principle
from others built in Europe or in this country, but its design was
carefully adapted to permit of interchangeable manufacture. No careful
finish was used except where indispensable. Special jigs, tools, and
fixtures were prepared. Ingenious wrinkles of American manufacture were
introduced. All this consumed time, and great was the irritation of the
general public. Under ordinary conditions, it would have taken years to
have developed the Liberty engine to the manufacturing stage, but under
the urgent stress of war, the whole work of design and preparation
for manufacture was crowded into a few short months, and then Liberty
engines began to be manufactured on a stupendous scale.
CUTTING WITH RED-HOT TOOLS
One of the most remarkable advances in machine tools was due to the
studies of Fred W. Taylor. He entered a large steel plant in 1880
and was immediately struck with the enormous waste of effort on the
part of the men in the plant. There was at that time considerable
dissatisfaction among the workmen, and when Taylor endeavored to speed
up work he was faced by the incontrovertible argument that he had no
idea how much work a certain machine ought to turn out. There was
nothing for him to do but either back down or study machine tools and
discover their maximum capacity. This led him to investigate the matter
of cutting speeds. For years he spent all of his spare time studying
this subject, timing machines and experimenting with different types
of cutting tools. He estimated that in the twenty-six years of his
investigation he converted 800,000 pounds of steel into chips. What
he wished to discover was the best depth of cut, the best speed of
cutting, and the best speed at which the tool should be fed into the
work. He soon discovered that, contrary to prevailing opinion, the
round-nosed tool was better than the diamond-pointed tool, that the
coarse slow-cutting speed was better than a fine cut at high speed. He
discovered that the best method of lubricating the tools was to keep
them bathed in a heavy stream of water, supersaturated with carbonate
of soda, so as to prevent the metal from rusting. The best tool steel
of that day was known as a self-hardening steel. Manufacturers of the
cutting steels had warned Taylor that he must not use water on these
tools. Taylor, however, was not satisfied to take the word of others,
but proceeded to investigate the matter himself, and discovered that
he could safely increase the cutting speed of his tools 33 per cent by
the use of a heavy stream of water for lubricating purposes. This led
Taylor and his associate, Maunsel White, to investigate the different
kinds of tool steels, and eventually they evolved a chrome tungsten
tool which could do from two to four times the work of other tools.
Later vanadium was added to the alloy, further improving the tool.
At the Exposition in Paris, in 1900, foreign manufacturers were
astonished to find enormous lathes operating at high speed with the
cutting tools taking such heavy cuts and feeding so fast that the nose
of the tool was actually heated to a dull red heat, and yet it kept its
cutting edge perfectly. This was a revelation to tool makers abroad,
and it led immediately to the adoption of American high-speed cutting
tools.
The development of the automobile, which began to take on serious
proportions at about that time, is responsible above all other machines
for improvements in American machine tools, and for the extension of
the American system of interchangeable manufacture. When automobiles
came to be made on the interchangeable system and in enormous
quantities so that the cost was reduced to within the limits of the
average man’s pocketbook, they began to make mechanics of men who
before that had never used a tool; and this new and widespread interest
in machinery stimulated the production of better and more efficient
tools. Hence the progress of machine tools in the past few years has
been simply phenomenal.