One Good Turn: A Natural History of the Screwdriver and the Screw (10 page)

The key to the success of Maudslay’s workshop was the precision lathe. The
Housebook
lathe had incorporated an early version of the slide rest; Leonardo had invented the moving cutter and interchangeable gears; and Plumier had described all-metal lathes. The eighteenth century saw many improvements to the lathe. In
1710
, a Swede built a lathe for accurate cutting of iron screws; fifty years later, a Frenchman completed an industrial lathe with a traversing carriage; around
1796
, a Rhode Island mechanic built an advanced lathe for screw-cutting; and, of course, Ramsden provided a striking example of precision screw-cutting. Yet it was Maudslay who synthesized all these features into a lathe capable of precision work on a large scale. In the process he produced the mother tool of the industrial age.

The heart of Maudslay’s lathe was an extremely accurate regulating screw. He built a machine that cut threads
of any pitch into soft metals such as tin and brass, then used these lead screws to make regulating screws of hard steel. “This beautiful and truly original contrivance became, in the hands of the inventor, the parent of a vast progeny of perfect screws, whose descendants, whether legitimate or not, are to be found in every workshop throughout the world, wherever first-class machinery is constructed,” wrote a contemporary.
⁸
It is important to understand the enormous impact of precision machine tools. It was not merely a question of supplanting manual labor. Steam engines, for example, simply could not have been built by hand—cylinders and piston rods required completely new standards of perfection. Precision opened the door to a mechanical world.

On Sundays, Maudslay would tour his quiet workshops to examine the work in progress. Chalk in hand, he would jot down his comments directly on his workmen’s benches. He particularly singled out examples of mechanical accuracy—or its lack. The ideal of precision was perhaps Maudslay’s greatest invention. He fabricated a regulating screw used in the manufacture of scientific instruments that was five feet long and two inches in diameter and was cut with fifty threads to the inch. He built himself a micrometer with a sixteen-inch-long screw that could measure to one ten-thousandth of an inch. It was used as the ultimate dimensioning standard by Maudslay’s employees, who nicknamed it the Lord
Chancellor. He provided each of his workers with a perfectly flat steel plate so that work in progress could periodically be placed on it to check if it was true. According to one of his assistants, these plates, which were filed and scraped by hand, were so smooth that “when placed over each other they would float upon the thin stratum of air between them until dislodged by time and pressure. When they adhered closely to each other, they could only be separated by sliding off each other.”
⁹

Maudslay also championed uniformity in screws. Surprisingly, this was a radical idea. Previously, each nut and bolt had been fabricated as a unique matching pair. “Any intermixture that occurred between them led to endless trouble and expense, as well as inefficiency and confusion,” observed one of his employees, “especially when parts of complex machines had to be taken to pieces for repairs.”
¹⁰
Maudslay adopted standardized taps and dies in his workshop, so that all nuts and bolts were made in a limited number of sizes. Now any nut would fit any bolt of the same size. This example inspired his pupil Joseph Whitworth, who in
1841
proposed a national standard for screw threads that eventually was adopted by all British manufacturers.
ⁱⁱⁱ

Whitworth was Maudslay’s successor as Britain’s great mechanical innovator. Unlike Maudslay, though, he was a manufacturer who also built specialized machine tools to order. The machine tools that came out of his factory were known throughout the world. They were versatile, dependable, and reasonably priced—and, incidentally, quite beautiful. It took a mechanical genius and a gifted craftsman like Maudslay to build the first precision lathe. Thanks to the machines that came from Whitworth’s Manchester works, any well-equipped workshop could routinely achieve similar accuracy. The high standards that Maudslay had set for himself had become universal.

Maudslay died in
1831
. He was interred in a cast-iron tomb of his own design. The inscription described him as “eminently distinguished as an engineer for mathematical accuracy and beauty of construction.”
¹¹
True enough, but a more moving epitaph was provided by one of his old workmen: “It was a pleasure to see him handle a tool of any kind, but he was
quite splendid
with an eighteen-inch file.”
¹²

I.
The old German word for screwdriver is
schraubendreher
(screw-turner), which originally meant the craft of turning screws, but came to refer to the tool itself.

II.
The prototype lock, prominently displayed in Bramah’s shopwindow, remained unpicked for more than fifty years. It was finally cracked by an American locksmith—it took him sixteen days.

III.
The Whitworth system was not international. When the United States developed its own, competing screw industry, it adopted a slightly different standard; continental Europe, which followed the metric system, likewise went its own way.

M
AUDSLAY HAD WHAT IS
Often called a mechanical bent. So did the men he trained. Whitworth was the best known, but there were others: Joseph Clement, whom Charles Babbage commissioned to build his famous difference engine, the calculating machine that anticipated the modern computer; Richard Roberts, whose metal planing machine was capable of such precision that he used it to manufacture iron billiard tables; and Maudslay’s personal assistant, James Nasmyth, who went on to invent the steam hammer and the pile driver. Like their master, these men generally came from modest backgrounds: Whitworth was the son of a schoolteacher; Clement’s father was a weaver; Roberts’s, a shoemaker. Moreover, they grew up not in cities but in small, remote villages or rural towns, without the least exposure to engineering. They often reached their calling by circuitous routes. Maudslay himself was apprenticed first to a carpenter; Roberts began as a quarryman; Clement was a slater’s assistant. Despite such unpromising
beginnings, all were attracted to the world of machines.

“My first essay at making a steam-engine was when I was fifteen,” Nasmyth told his biographer. “I then made a real working steam-engine,
1
³
/
₄
diameter cylinder, and
8
-in. stroke, which not only could act, but really did some useful work; for I made it grind the oil colors which my father required for his painting.”
¹
Nasmyth’s background was different from that of his colleagues. He was born in a large city, Edinburgh, to a prosperous family—his father was the well-known Scottish landscape painter Alexander Nasmyth. James attended the High School in Edinburgh, the School of Art, and the university. In his spare time he continued his mechanical experiments with steam engines, casting parts in his bedroom, hanging around machine shops. The municipality was debating the wisdom of adopting steam-powered carriages for public roads, and Nasmyth achieved a small measure of local renown by building a vehicle that carried eight persons. This was more than two decades after George Stephenson built the first steam road-carriage, but it was still a remarkable accomplishment for a self-taught young man not yet twenty. Finally, having determined to pursue a career in mechanical engineering, Nasmyth decided to apprentice under the famed Henry Maudslay. He traveled to London and presented himself to the great man, bringing
with him a working model of a steam engine. Maudslay, who no longer took pupils, spent twenty minutes examining the beautifully made engine, then took the young man on as his personal assistant.

Maudslay recognized in Nasmyth traits shared by all these men: an innate love of mechanics, a natural aptitude for working with metals, and above all a devotion to precision. Precision was an absolute standard. Maudslay, for example, produced regulating screws of much greater accuracy than was required by industry at the time; Whitworth built himself a micrometer that was accurate to one-millionth of an inch. These men are called engineers, but this designation is inadequate. For one thing, they were working in uncharted territory in which invention as well as technical proficiency was required. They were not simply designing replacements for traditional craft methods; they were inventing tools that were capable of previously unimagined accuracy. Moreover, these were also extremely skilled craftsmen. Indeed, the ability to actually make—with their own hands—what they conceived is an integral part of their achievements. “It is one thing to invent,” observed Marc Brunel, “and another thing to make the invention work.”
²

An affinity for steel and iron is a gift, like perfect pitch for a musician. These engineers had the artist’s independence. Joseph Clement once received an order from America for a large regulating screw to be made “in
the best possible manner.” He produced an object of unparalleled accuracy and submitted a bill for several hundred pounds to his shocked client, who had expected to pay at most twenty (the case went before arbitrators and the American lost). In another case, Isambard Kingdom Brunel, who was in charge of building the Great Western Railway, commissioned Clement to design a piercing locomotive whistle. Delighted with the prototype, Brunel ordered a hundred. He, too, was shocked at the high price and declared that it was six times what he had previously been paying. “That may be,” responded Clement, “but mine are more than six times better. You ordered a first-rate article, and you must be content to pay for it.”
³
He won that case, too.

Mechanical genius is less well understood and studied than artistic genius, yet it surely is analogous. “Is not invention the poetry of science?” asked E. M. Bataille, a French pioneer of the steam engine. “All great discoveries carry with them the indelible mark of poetic thought. It is necessary to be a poet to create.”
⁴
Nevertheless, while most of us would bridle at the suggestion that if Cézanne, say, had not lived, someone else would have created similar paintings, we readily accept the notion that the emergence of a new technology is inevitable or, at least, determined by necessity. My search for the best tool of the millennium suggests otherwise. Some tools were developed in direct response to a particularly
vexing problem—this was the case with the Roman frame saw, or the socketed hammer. No doubt these devices would have appeared sooner or later. But the sudden and “mysterious” appearance of tools such as the carpenter’s brace or the medieval bench lathe cannot be explained by necessity. Such tools are the result of leaps of an individual’s creative imagination. They are the product of brilliant, inventive minds whose intuitive perceptions of complex mechanical relationships really are poetic.

—

The screwdriver is hardly poetic. The pragmatic way in which the arquebusier’s spanner and the armorer’s pincers were modified to include a screwdriver, or the casual combination of a screwdriver bit with a carpenter’s brace, suggest expediency rather than invention. The screw itself, however, is a different matter. It is hard to imagine that even an inspired gunsmith or armorer—let alone a village blacksmith—simply happened on the screw by accident. To begin with, the thread of a screw describes a particularly complicated three-dimensional shape, often misnamed a spiral. In fact, a spiral is a curve that winds around a fixed point with a continuously increasing radius. A clock spring forms a spiral; so does a rope neatly coiled on the deck of a sailing ship. A helix, on the other hand, is a three-dimensional curve that twists around a cylinder at a constant inclined angle.
So-called spiral staircases and spiral bindings are both examples of helixes. So, of course, are screws.

The helix occurs in nature in the form of the climbing vine and in some seashells.
^I
But it requires a particular set of talents to invent a screw. First, it would take a skillful mathematician to describe the geometry of the helix. Then he—or someone else—would have to make the connection between theoretical mathematics and practical mechanics in order to imagine a use for such an unusual object. Finally, there would be the problem of how to actually fabricate a screw.

The builder of the
Housebook
lathe, whoever he was, resolved the problem of how to make a screw, but he did not invent the screw itself. An understanding of the principle of the screw predates the fifteenth century. The first documented use of the word
screw,
according to the
Oxford English Dictionary,
is in
1404
. It occurs in a list of accounts: “Item
1
rabitstoke cum
2
scrwes” (the word was also spelled
skrew, skrue,
and
scrue
). A rabitstoke, I learn, is a plane for shaping complicated grooves, or rabbets; the two wooden screws, holding an adjustable fence, are part of the tool.
⁵
Small wooden screws were also used to make bench vises and assorted
clamps; large wooden screws adjusted the vertical and horizontal angle of cannons.

The most famous use of screws in the Middle Ages was in printing presses. Johannes Gutenberg played a pivotal role in the invention of movable type in the mid-
1400
s; unfortunately, there is no surviving description of his press. The earliest known representation of a printing press is about fifty years later. It consists of a heavy wood frame with a crosspiece through which a large screw is threaded. The screw is turned by means of a handspike, or lever, and pushes down a wooden board, which in turn presses the paper against the inked type.