Free The Dawn of Innovation by Charles R. Morris Page B

numbered ring is marked in 5-degree intervals. The six inner concentrics subdivide to an accuracy of 50 minutes. The right-hand heavy line from the origin intersects at the 150-minute mark, so the angle measures 5 degrees plus 150 minutes = 7,5 degrees. C. The Vernier Caliper uses a second sliding rule to mark out very small distances. In the example, the caliper marking is beyond the.30 position on the fixed scale. The additional distance is read from the vernier scale at the point where it lines up most closely with a marking on the fixed scale, as shown. 5Humans are very good at recognizing when two moving lines line up—"vernier acuity.")

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    D. Using geometrics mehods, an artisan could mark reasonably-accurate divisions on a large disc, and then capture those same proportions on a much smaler workpiece, as shown. Note that the index wheel includes several choices of toothh arrangemenr and that the index pointer fixes the index wheel and the workpiece in position for each cut. E. A pocket-sized thousandth of an inch micrometer first appeared in the catalog of the Providence firm of brown and Sharpe in 1877, and marked a high point of convenient recision in the nineteenth century. The micrometers are still in wide use. The numbered divisions on the barrel signify tenths (0.1) of an inch. Each smaller division is a fortieth (0.025) of an inch, while each small numbered marking on the handle is a thousandth (0.001) of inch In the illustration the readout on the barrel is 0.125 inches, plus an additional .001 on the handle = 0.126 inches.

    The great figure in screw threads was Henry Maudslay, one of the greatest machinists of all time. Although he ran a large establishment in his later years, he was at heart a shop-floor machinist. He also appears to be have been a man of immense calm and good humor, certainly comfortably fat in his later years. His workers adored him, almost as much as they admired his technical skills. One recounted fondly, “It was a pleasure to see him handle a tool of any kind, but he was quite splendid with an eighteen-inch file.” 16 Maudslay’s permanent contribution was to stabilize machining at very high levels of precision, hardly surpassed to the present day.
    When Maudslay began his career, screw threads were in a state of disarray with respect to pitch (thread count), shape, angle, and uniformity, and they became his pet project. While he did not invent the modern screw-cutting lathe—Ramsden anticipated much of his work—his first versions achieved such a high pitch of perfection that they became the standard for all such instruments.
    In a traditional lathe, the worker held the cutting tool against the rotating workpiece. In the Maudslay screw-cutting lathe, first produced between 1797 and 1800, before he was thirty, the workpiece was positioned on a slide by a long lead screw, the cutting depth of the tool was set by a screw-driven micrometer, and a gear-set controlled the thread count of the new screw by varying the speed of the workpiece rotation relative to its lateral motion on the slide. Different gear settings allowed reliable production of a variety of thread pitches. The gearing on one early machine accommodated twenty-eight different thread pitches. One Maudslay-produced screw, created for a dividing engine to be used in the production of large astronomical instruments, was five feet long and two inches in diameter, with 50 threads per inch, or 3,000 threads in all; it came with a foot-long nut with 600 threads. No one before Maudslay could have produced such an instrument.
    Maudslay’s obsession with accuracy pervaded every aspect of his machinery, since vibrations, misalignments, or slightly loose fittings make a
mockery of ultraprecise tool settings. Maudslay’s constructions set new standards for solidity, stability, and perfection with respect to planes, angles, and uniformity of motion. He built a bench micrometer to measure deviances of a