One Good Turn: A Natural History of the Screwdriver and the Screw (7 page)

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By the mid-sixteenth century, applications for screws had grown to include miniature screws and bolts in watches, larger screws in guns, and heavy bolts in armor. Yet it was another two hundred years before demand grew enough that a screw industry developed.
The
Encyclopédie
mentions that the region of Forez, near Lyon, specialized in screws, which were available in a variety of lengths—one-half inch to four or five inches. These screws were still so expensive that they were sold individually. According to the
Encyclopédie,
heads were either slotted or square.

In England, screw-making was concentrated in the Midlands. It was organized as a cottage industry. Forged-steel blanks with formed heads were made in large quantities by local blacksmiths and delivered to the so-called girder, who, with his family and an assistant or two, worked at home. The first step was to cut the slot, or “nick,” into the head with a hacksaw. That was the easy part. Next the thread, or “worm,” had to be filed by hand. Some girders used a spindle—a crude lathe—turning a crank with one hand and guiding a heavy cutter with the other, back and forth, back and forth. Whichever method was used, the work was slow and laborious, and since the worm was cut by eye, the result was a screw with imperfect, shallow threads. According to one contemporary observer, who had seen screw-girders at work, “The expensive and tedious character of these processes rendered it impossible for the screws to compete with nails, and consequently the sale was very small. The quality was also exceedingly bad, it being impossible to produce a well-cut thread by such means.”
⁴

Both Moxon and the
Encyclopédie
mention that screws are used by locksmiths to fasten locks to doors. I also come across references to eighteenth-century carpenters using screws to attach hinges, particularly the novel garnet hinge. A garnet hinge resembles a |—, the vertical part being fastened to the doorjamb and the horizontal to the door. Garnet hinges, used with light cupboard doors and shutters, were screwed rather than nailed to the frame. Heavy doors, on the other hand, were hung on traditional strap hinges that extended the full width of the door and were nailed and clenched.

Strap and garnet hinges are still used today, but by far the most popular modern door hinge is the butt hinge, which is not mounted on the surface but mortised into the thick end—the butt—of the door. Butt hinges are aesthetically pleasing, being almost entirely hidden when the door is closed. They were used in France as early as the sixteenth century (butt hinges are illustrated by Ramelli), but were luxury objects, crafted by hand of brass or steel. In
1775
, two Englishmen patented a design for mass-producing cast-iron butt hinges.
⁵
Cast-iron butt hinges, cheaper than strap hinges, had one drawback: they could not be nailed. Nails worked themselves loose as the door was repeatedly opened and closed, and since the nails were in the butt of the door, they could not be clenched. Butt hinges had to be screwed.

By coincidence, at the very moment that butt hinges were being popularized, a technique for manufacturing good-quality, inexpensive screws was being perfected. Years earlier, Job and William Wyatt, two brothers from Staffordshire in the English Midlands, had set out to improve screw-making. In
1760
, they patented a “method of cutting screws of iron commonly called wood-screws in a better manner than had been heretofore practiced.”
⁶
Their method involved three separate operations. First, while the forged blank of wrought iron was held in a rotating spindle, the countersunk head was shaped with a file. Next, with the spindle stopped, a revolving saw-blade cut a slot into the head. Finally, the blank was placed in a second spindle and the thread was cut. This was the most original part of the process. Instead of being guided by hand, the cutter was connected to a pin that tracked a lead screw. In other words, the operation was automatic. Now, instead of taking several minutes, a girder could turn out a screw—a much better screw—in six or seven
seconds.

It took the Wyatt brothers sixteen years to raise the capital required to convert a disused water corn-mill north of Birmingham into the world’s first screw factory. Then, for unexplained reasons, their enterprise failed. Maybe the brothers were poor businessmen, or maybe they were simply ahead of their time. A few years later, the factory’s new owners, capitalizing on
the new demand for screws created by the popularity of butt hinges, turned screw manufacturing into a phenomenal success. Their thirty employees produced sixteen thousand screws a day.
⁷

Machine-made screws were not simply produced more quickly, they were much better screws. Better and cheaper. In
1800
, British screws cost less than tuppence a dozen. Eventually, steam power replaced waterpower in the screw factories, and a series of improvements further refined the manufacturing process. Over the next fifty years, the price dropped by almost half; in the following two decades, it dropped by half again. Inexpensive screws found a ready market. They proved useful not only for fastening butt hinges but for any application where pieces of thin wood needed to be firmly attached, which included boatbuilding, furniture-making, cabinetwork, and coachwork. Demand increased and production soared. British screw factories, which had annually produced less than one hundred thousand gross in
1800
, sixty years later produced almost
7
million gross.
⁸

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Take a close look at a modern screw. It is a remarkable little object. The thread begins at a gimlet point, sharp as a pin. This point gently tapers into the body of the screw, whose core is cylindrical. At the top, the core tapers into a smooth shank, the thread running out to nothing. The
running-out is important since an abrupt termination of the thread would weaken the screw.

The first factory-made screws were not like this at all. For one thing, although handmade screws were pointed, manufactured screws had blunt ends and were not self-starting—it was always necessary first to drill a lead hole. The problem lay in the manufacturing process. Blunt screws could not simply be filed to a point—the thread itself had to come to a point, too. But lathes were incapable of cutting a tapering thread. Screw manufacturers tried angling the cutters, which produced screws that tapered along their entire length. Such screws had poor holding power, however, and carpenters refused to use them. What was needed was a machine that could cut a continuous thread in the body of the screw (a cylinder) and also in the gimlet point (a cone).

An inventive American mechanic found the solution. The first American screw factories had been established in Rhode Island in
1810
, using adapted English machines. Providence became the center of the American screw industry, which by the mid-
1830
s was experiencing a boom in demand for its products. Beginning in
1837
, a series of patents addressed the problem of manufacturing gimlet-pointed screws, but it took more than a decade of trial and error to get it right. In
1842
, Cullen Whipple, a mechanic from Providence who worked for the New England Screw Company, invented a method of manufacturing
screws on a machine that was entirely automatic. Seven years later he made a breakthrough and successfully patented a method of producing pointed screws. A slightly different technique was devised by Thomas J. Sloan, whose patent became the mainstay of the giant American Screw Company. Another New Englander, Charles D. Rogers, solved the problem of tapering the threaded core into the smooth shank. Such advances put American screw manufacturers firmly in the lead, and by the turn of the century, when the screw had achieved its final form, American methods of production dominated the globe.

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Ever since the fifteenth century, screws had had either square or octagonal heads, or slots. The former were turned by a wrench, the latter by a screwdriver. There is no mystery as to the origin of the slot. A square head had to be accurate to fit the wrench; a slot was a shape that could be roughly filed or cut by hand. Screws with slotted heads could also be countersunk so they would not protrude beyond the surface—which was necessary to attach butt hinges. Once countersunk screws came into common use in the early
1800
s, slotted heads—and flat-bladed screwdrivers—became standard. So, even as screws were entirely made by machine, the traditional slot remained. Yet slotted screws have several drawbacks. It is easy to “cam out,” that is, to push the screwdriver
out of the slot; the result is often damage to the material that is being fastened or injury to one’s fingers—or both. The slot offers a tenuous purchase on the screw, and it is not uncommon to strip the slot when trying to tighten a new screw or loosen an old one. Finally, there are awkward situations—balancing on a stepladder, for example, or working in confined quarters—when one has to drive the screw with one hand. This is almost impossible to do with a slotted screw. The screw wobbles, the screwdriver slips, the screw falls to the ground and rolls away, the handyman curses—not for the first time—the inventor of this maddening device.

American screw manufacturers were well aware of these shortcomings. Between
1860
and
1890
, there was a flurry of patents for magnetic screwdrivers, screw-holding gadgets, slots that did not extend across the face of the screw, double slots, and a variety of square, triangular, and hexagonal sockets or recesses. The latter held the most promise. Replacing the slot by a socket held the screwdriver snugly and prevented cam-out. The difficulty—once more—lay in manufacturing. Screw heads are formed by mechanically stamping a cold steel rod; punching a socket sufficiently deep to hold the screwdriver tended to either weaken the screw or deform the head.

The solution was discovered by a twenty-seven-year-old
Canadian, Peter L. Robertson. Robertson was a so-called high-pitch man for a Philadelphia tool company, a traveling salesman who plied his wares on street corners and at country fairs in eastern Canada. He spent his spare time in his workshop, dabbling in mechanical inventions. He invented and promoted “Robertson’s
20
th Century Wrench-Brace,” a combination tool that could be used as a brace, a monkey wrench, a screwdriver, a bench vise, and a rivet maker. He vainly patented an improved corkscrew, a new type of cuff links, even a better mousetrap. Then, in
1907
, he received a patent for a socket-head screw.

Peter L. Robertson’s
1907
patent for a socket-head screw.

Robertson later said that he got the idea for the socket head while demonstrating a spring-loaded screwdriver to a group of sidewalk gawkers in Montreal—the blade slipped out of the slot and injured his hand. The secret of his invention was the exact shape of the recess, which was square with chamfered edges, slightly tapering sides, and a pyramidal bottom. “It was early discovered that by the use of this form of punch, constructed with the exact angles indicated, cold metal would flow to the sides, and not be driven ahead of the tools, resulting beneficially in knitting the atoms into greater strength, and also assisting in the work of lateral extension, and without a waste or cutting away of any of the metal so treated, as is the case in the manufacture of the ordinary slotted head screw,” he rather grandly explained.
⁹

An enthusiastic promoter, Robertson found financial backers, talked a small Ontario town, Milton, into giving him a tax-free loan and other concessions, and established his own screw factory. “The big fortunes are in the small inventions,” he trumpeted to prospective investors. “This is considered by many as the biggest little invention of the
20
th century so far.”
¹⁰
In truth, the square socket really was a big improvement. The special square-headed screwdriver fit snuggly—Robertson claimed an accuracy within one one-thousandth of an inch—and never cammed out. Craftsmen, especially furniture-makers and boatbuilders, appreciated the convenience of
screws that were self-centering and could be driven with one hand. Industry liked socket-head screws, too, since they reduced product damage and speeded up production. The Fisher Body Company, which made wood bodies in Canada for Ford cars, became a large Robertson customer; so did the new Ford Model T plant in Windsor, Ontario, which soon accounted for a third of Robertson’s output. Within five years of starting, Robertson built his own wire-drawing plant and powerhouse and employed seventy-five workers.

In
1913
, Robertson decided to expand his business outside Canada. His father had been a Scottish immigrant, so Robertson set his sights on Britain. He established an independent English company to serve as a base for exporting to Germany and Russia. The venture was not a success. He was thwarted by a combination of undercapitalization, the First World War, the defeat of Germany, and the Russian Revolution. Moreover, it proved difficult to run businesses on two continents. After seven years, unhappy English shareholders replaced Robertson as managing director. The English company struggled along until it was liquidated in
1926
. Meanwhile, Robertson turned to the United States. Negotiations with a large screw manufacturer in Buffalo broke down after it became clear that Robertson was unwilling to share control over production decisions. Henry Ford was interested, since his Canadian plants were reputedly
saving as much as $
2
.
60
per car using Robertson screws. However, Ford, too, wanted a measure of control that the stubborn Robertson was unwilling to grant. They met but no deal was struck. It was Robertson’s last attempt to export his product. A lifelong bachelor, he spent the rest of his life in Milton, a big fish in a decidedly small pond.