Exactly: How Precision Engineers Created the Modern World. Simon Winchester

in the sixteenth century, with the concept of the leadscrew. This was a long and (most often, in early times) wooden screw that was mounted under the main frame of the lathe and could be turned by hand to advance the movable end of the lathe toward or away from the fixed end. It could do so with a degree of precision; one turn of the handle might advance the movable part of the lathe by an inch, say, depending on the pitch of the leadscrew. It gave wood turners working on a lathe a much greater degree of control, and allowed them to produce things (chair legs, chess pieces, handles) of great decorative beauty, symmetric loveliness, and baroque complexity.

      Henry Maudslay then improved the lathe itself by many orders of magnitude—first by making it of iron, forging its structure stoutly and heavily, and at a stroke allowing it not merely to machine wooden items, but also to create symmetry out of shapeless billets of hard metal, which the flimsy lathes of old were incapable of doing. This alone might have been sufficient for us to remember the man, but then Maudslay employed one further component on his working lathes, a component whose origins are debated still, however, with the tenor of the debate pointing to an endless argument that complicates the historiography of precision and precision engineering.

      

       Henry Maudslay, once a “tall, comely fellow,” machined the innards of Bramah’s locks and went on to become the founding father of precision toolmaking, mass production, and the key engineering concept of achieving perfect flatness.

      Specifically, the device in question mounted on Maudslay’s lathes is known as a slide rest, a part that is massive, strongly made, and securely held but movable by way of screws, and is intended to hold any and all of the cutting tools. It is filled with gears that allow for the adjustment of the tool or tools to tiny fractions of an inch, to permit the exact machining of the parts to be cut. The slide rest is necessarily placed between the lathe’s headstock (which incorporates the motor and the mandrel that spins the workpiece around) and the tailstock (which keeps the other end of the workpiece secure). The leadscrew—Maudslay’s was made of metal, not wood, and with threads much closer together and with a more delicate pitch than was possible for a wooden version—advances the workpiece. The tools held on the slide rest can then be moved across the path of travel dictated by the leadscrew, thereby allowing the tools to make holes in the workpiece, or to chamfer it or (in due course, once milling had been invented, a process related in the next chapter) mill it or otherwise shape it to the degree that the lathe operator demands. So the leadscrew moves the workpiece longitudinally, and the slide rest that holds the tools that cut or chamfer or make holes in the workpiece moves transversely, or in all sorts of directions that are across the path made by the leadscrew.

      Metal pieces can be machined into a range of shapes and sizes and configurations, and provided that the settings of the leadscrew and the slide rest are the same for every procedure, and the lathe operator can record these positions and make certain they are the same, time after time, then every machined piece will be the same—will look the same, measure the same, weigh the same (if of the same density of metal) as every other. The pieces are all replicable. They are, crucially, interchangeable. If the machined pieces are to be the parts of a further machine—if they are gearwheels, say, or triggers, or handgrips, or barrels—then they will be interchangeable parts, the ultimate cornerstone components of modern manufacturing.

      Of equally fundamental importance, a lathe so abundantly equipped as Maudslay’s was also able to make that most essential component of the industrialized world, the screw.

      Over the centuries, there were many incremental advances in screw making, as we shall see, but it was Henry Maudslay (once he had invented or mastered or improved or in some other manner become intimately associated with the slide rest on his lathe) who then devised a means of cutting metal screws, efficiently, precisely, and fast. Much as Bramah had a lock in his workshop window on Piccadilly, for reasons of pride as much as for his famous challenge, so Maudslay, Sons and Field placed in the bow window of the firm’s first little workshop, on Margaret Street in Marylebone, a single item of which the principal was most proud—and that was a five-foot-long, exactly made, and perfectly straight industrial screw made of brass.

      Technically, Maudslay was not the first to perfect a screw-making lathe. Twenty-five years earlier, in 1775, Jesse Ramsden, a scientific instrument maker in Yorkshire who was funded by the same Board of Longitude for which the clockmaker John Harrison had labored, and who was not allowed to patent his invention, had made a small and exquisite screw-cutting lathe. This could cut tiny screws with as many as one hundred twenty-five turns to the inch—meaning it would take one hundred twenty-five turns to advance the screw by one inch—and so would allow the tiniest adjustments to any device to which the screw was harnessed. But Ramsden’s was effectively a one-off machine, as delicate as a watch, meant for work with telescopes and navigational instruments, and in no way destined for the making of large-scale devices made of much metal and that could work at great speed and maintain accuracy and be durable. What Maudslay had done with his fully equipped lathe was to create an engine that, in the words of one historian, would become “the mother tool of the industrial age.”

      Moreover, with a screw that was made using his slide rest and his technique, and with a lathe constructed of iron and not with the wooden frame he and Bramah had used initially, he could machine things to a standard of tolerance of one in one ten-thousandth of an inch. Precision was being born before all London’s eyes.

      So, whoever did invent the slide rest can take the credit for the later precise manufacture of countless components of every conceivable size and shape and relevance to a million and one machined objects. The slide rest would allow for the making of myriad items, from door hinges to jet engines to cylinder blocks, pistons, and the deadly plutonium cores of atomic bombs—as well as, of course, the screw.

      But just who did invent it? Not a few say Henry Maudslay, and that he did so in Joseph Bramah’s “secret workplace [which] contained several curious machines … constructed by Mr. Maudslay with his own hands.” Others say it was Bramah. Still others refute the idea of Maudslay’s involvement entirely, saying definitively that he did not invent it, nor ever claimed to have done so. Encyclopedias say the first slide rest was actually German, having been seen illustrated in a manuscript in 1480. Andrey Nartov, the Russian scientist who had the eighteenth-century title of personal craftsman to Tsar Peter the Great, was revered as the greatest teacher of lathe operation in Europe (and taught the methods to the then-king of Prussia) and is said to have made a working slide rest (and taken it to London to show it off) as early as 1718. And just in case the story from St. Petersburg has any doubters, a Frenchman named Jacques de Vaucanson quite provably made one in 1745.

      Chris Evans, a professor in North Carolina who has written extensively about the early years of precision engineering, notes the competing claims, and cautions against the “heroic inventor” treatment of the story. Far better to acknowledge, he says, that precision is a child of many parents, that its advances invariably overlap, that there are a great many indeterminate boundaries between the various disciplines to which the word precision can be attached, and that it was, in its early days, a phenomenon that evolved steadily over three centuries of ever-lessening bewilderment. It is, in other words, a story far less precise than its subject.

      That being said, Henry Maudslay’s principal legacy is a wholly memorable one, for other inventions and involvements followed his association with Joseph Bramah, from whose employ he left, in a huff, after his request for a raise—he was making thirty shillings a week in 1797—was turned down too curtly for his taste.

      MAUDSLAY PROMPTLY PROCEEDED to free himself from the circumscribed world of West London lock making, and he entered—one might say, he inaugurated—the very different world of mass production. He created in the process the wherewithal for making, in truly massive numbers, a vital component for British sailing ships. He built the wondrously complicated machines that would, for the next one hundred fifty years, make ships’ pulley blocks, the essential parts of a sailing ship’s rigging that helped