An Encyclopedia of the History of Technology part 42 pptx

PART TWO: POWER AND ENGINEERING 392 in the direction of increasing the accuracy of measurement and in this the screw is of major importance. The ability to manufacture accurate screw threads has been critical in the design of instruments for astronomy, navigation, time measurement, the production of screw controlled machine tools and engineering inspection devices. The measurement of time, based on observation of the sun’s passage, has always exercised the mind of man and many methods have been explored. By the ninth century AD the Chinese had combined hydraulic and mechanical methods to make a large water clock which showed the time by ringing bells and the appearance of various figures. The first all-mechanical clocks were made in Europe, the most outstanding example being that produced by Giovanni de Dondi, c. 1364, which incorporated elliptical gear wheels and sun and planet gears, all cut by hand. A replica has been exhibited in the Science Museum, London. The oldest clock in England is that at Salisbury Cathedral, constructed c. 1386 in a similar way with forged iron gears and lantern pinions, all held in an iron framework joined by rivets and wedges. These construction methods, while adequate for large public clockwork, were not suitable for the smaller timekeepers which the people sought, and the size of this demand and the development of the designs led to improvements in machining, including accurately cut gears, turned spindles and screws which were in advance of general manufacturing by 300 years. During this period the spring-driven pocket watch made its appearance and with it the need for a device to control the pull of the spring to exert a constant force throughout its unwinding. The, fusee, invented c. 1450, consists of a conical drum with a spiral groove carrying a chain or cord which, attached to the end of the spring, controls its force by unwinding from a different part of the drum as the spring runs down. Manufacturing fusees called for an extension to the machining capacity of the small allmetal lathe already used by the clockmaker to make accurate spindles and called a turn. This rigid bow-driven device gave the precision necessary to produce small parts with the repeatability required for production purposes and exemplified one of the key features of modern machine tools. Simple fusee engines, employing a screw-controlled linear motion but hand-controlled in-feed to the profile, were designed from 1740, but by 1763 Ferdinand Berthoud had made an engine which was automatic in fixing the relationship between cutting tool and work, thereby illustrating our second principle of machine tool design by eliminating hand skill. Figure 7.2 shows an example of this type of machine. GENERAL MACHINE TOOLS Clockmakers also required accurate screw threads and these had been cut by machine since c. 1480 by the master screw method. The earliest representation, in the Mittelalterliche Hausbuch, shows this design, which produces a thread if a ENGINEERING AND PRODUCTION 393 cutting tool with a suitable ‘V’ profile is held against the workpiece and the crank handle turned to advance the work according to the pitch of the master thread. This method will only cut a thread of the same pitch as the master screw; the artist did not understand its function, as the threads shown are opposite handed. Many similar machines were constructed on the master screw principle, such as that of Emanuel Wetschgi, c. 1700. However, greater flexibility in screw making was achieved by the use of a sliding spindle controlled by a set of master threads brought into mesh as required. Plumier’s lathe of 1701 used this system, which was continued in Holtzapffel’s lathe of 1785. The use of gearing and leadscrew to obtain alternative screw pitches is attributed to Leonardo da Vinci in his machine design of c. 1500, which shows the principles of an industrial machine capable of producing machine leadscrews. Developments from this are first shown in the design of Jacques Besson, the successor to Leonardo as engineer to the French court, in his machine of 1578. This machine is the first example of the leadscrew and nut guidance and drive combination of later machines; however, despite its massive wooden frame and resultant rigidity, its driving system would not provide a high degree of precision and this line of development represents the beginning of the ideas of ornamental turning. Another machine of 1578 by Besson has cams and templates, enabling copies of many shapes to be produced, and the use of similar techniques and machines became a hobby of high society in Europe. Beautiful and intricate decorative objects were produced on machines of increasing complexity, involving: sliding spindles, rosette cams, overhead drive to tools held in the cross slide, and gear and cam controlled geometric work-holding devices and cutting frames. Ornamental lathes, still in mainly wooden frames and with treadle drives, were being produced in the twentieth century by firms such as Holtzapffel, see Figure 7.3. Figure 7.2: A watch-maker’s fusee and screw-cutting lathe of the eighteenth century. PART TWO: POWER AND ENGINEERING 394 Instrument makers had special problems involving the need for accurate screws to be used in obtaining precise linear and circular divisions. Jesse Ramsden’s screwcutting lathes of 1777 and 1778 were designed for this purpose, the latter to make a very accurate screw for his dividing engine to measure off accurate intervals in straight lines. The tangent screw, cut on his lathe of 1777 using gear wheels with large numbers of teeth to obtain the fine correction of pitch required, was used in turn to drive a very large gear wheel with a central boss carrying one end of a steel strip which, when it unwinds, controls the travel of the cutting tool. Other gears control the relative rotation of the tangent screw shaft and the workpiece to generate screws of high precision and any length within the capacity of the machine. While these developments of lathes to meet the special needs of clockmaker, instrument maker and ornamental turner were taking place, the general industrial lathe for work on wood, ivory or soft metals continued in a simple wooden frame with band drive until the end of the seventeenth century. In his book L’Art du Tourneur, published in 1701, Plumier describes special features of machine design for an iron turning lathe, specifying spindle materials, bearings and the shape and sharpening of the cutting tool. Mounting of the work Figure 7.3: Holtzapffel ornamental turning lathe of 1815. ENGINEERING AND PRODUCTION 395 between centres, and the strength and rigidity to maintain the precision required under the heavy cutting loads in machining metal, were also to form the basis of the design of metal cutting machine tools thereafter. Christopher Polhem of Sweden in about 1716 produced an iron cutting lathe which incorporated a screw drive to the cutting tool driven by the same water wheel that turned the work spindle and was of the heavy construction required to give precision in the turning of rollers for his mills. In 1760, Vaucanson produced an industrial lathe within a heavy framework of iron bars solidly bolted together and carrying substantial centres for work holding, although the size was limited by the framework. The carriage for the toolholder is mounted on square bars utilizing the 45° faces for the most precise support and driven by a leadscrew manually operated. Senot’s lathe of 1795 includes the change wheels envisaged by Leonardo and used later by clockmakers to give a screw pitch choice from the leadscrew, and incorporates lubricated bearings to take the heavy cuts of screw cutting in hard metal; it was much more convenient to use than that of Vaucanson. In 1797 the true industrial lathe came into being through the genius of Henry Maudslay, who created a machine which was the synthesis of all previously recognized desirable features: rigid construction, prismatic guide bars for the carriage, change gear drive from spindle to leadscrew, graduated in-feed for the tool holder and substantial centres for work holding, readily adjustable for length by moving the tailstock. With this lathe Maudslay was able to cut precision screws of a range of pitches to a high degree of repeatability and he is regarded as the ‘father of the industrial lathe’. Figure 7.4 illustrates Maudslay’s lathe. At about the same time David Wilkinson in the USA produced his screw-cutting industrial lathe which bears a strange resemblance to that of Leonardo da Vinci nearly 300 years earlier. Although of heavy construction throughout, with guideways 5.5–6m (18–20ft) long, it could only cut screws of the same pitch and length as its leadscrew as no change gears were incorporated and little adjustment to the centre position. In 1806, Wilkinson made a large general purpose lathe with screw drive to the carriage which was used extensively and earned him regard as the founder of the American machine tool industry. While this general development of the lathe was in progress, special needs of manufacturing in different fields was being met in a variety of ways. The need for accurate gear wheels in clock and instrument making brought into being the dividing engine: the example from c. 1672 in the Science Museum, London, is the earliest machine tool in the collection. A formed rotary file cuts the teeth of the gear in turn indexed using a plate containing a number of hole circles. Very little difference is apparent between this machine and those of 100 years later, although in 1729 Christopher Polhem had developed a hand- operated gear cutting machine of a production type using reciprocating broaches to cut the teeth of a number of wheels on separate vertical spindles. PART TWO: POWER AND ENGINEERING 396 The broaches were later changed for rotary cutters and formed part of a series of machines for large-scale production of clocks. The shape of teeth for gearing had exercised the minds of mathematicians and clock and instrument makers since the fifteenth century and the work of Phillipe de la Hire in 1694 contains a detailed mathematical analysis of different forms, concluding that the involute was the best profile. This form was not adopted in practice for 150 years and the clockmakers’ products were only adequate for their time until Rehe’s engine of 1783 which used formed cutters instead of rotary files and was regarded as a real gear cutting machine. Engineering grew out of military campaigning and machine tool developments owe a great deal to the ingenuity exercised in producing the engines of war. The Pirotecnica of 1540 by Biringuccio shows a water-powered cannon boring mill, with the cannon mounted on a movable carriage and the tool entering and finishing the cored hole in the casting. This method, although inaccurate, continued until the eighteenth century. About 1713, Maritz invented a vertical boring mill which was capable of boring cannon from solid, but, dissatisfied with the operation of this type of machine in the Netherlands State Gun Foundry at The Hague, Jan Verbruggen, the Master Figure 7.4: Henry Maudslay’s original screw cutting lathe of 1797. ENGINEERING AND PRODUCTION 397 Founder, produced in 1795 a horizontal boring mill which employed a stationary boring bar and rotated the cannon in bearings. This type of machine was introduced in the Royal Arsenal at Woolwich when Verbruggen was appointed Master Founder there in 1770. With the development of the steam engine (see Chapter 5) the need for machines to bore much larger diameters were met by designs based on the cannon borers with devices to reduce the inaccuracy inherent in the use of a long, unsupported boring bar. John Smeaton’s mill at the Coalbrook Company’s Carron Ironworks employed a travelling carriage running inside the casting to support the end of the boring bar. These methods were all unsatisfactory, as the cutter tended to follow the cast profile and it was not until John Wilkinson produced his cylinder boring machine in 1776 (Figure 7.5) that it became possible to correct run-out in the bore to produce a cylinder sufficiently accurate to satisfy the design of James Watt’s steam engine. Wilkinson’s Bersham Ironworks and his other foundries were in turn the first to use Watt’s engines for industrial power: he was the greatest ironmaster of his generation and the father of the Industrial Revolution, with his cylinder boring mill the first truly industrial machine tool. The machine consisted of a carriage on which the cylinder to be bored was securely mounted with the boring bar, running through its centre, fixed in bearings at each end, one of which was driven through gearing from a water wheel. The boring bar was hollow, with a rod running through its centre which advanced the cutter head along the revolving bar by means of a longitudinal slot and a slider attached to the cutter head and traversed by a rack and gear, with a weighted lever to provide the moving force. The use of rack and slotted keyway for tool traverse are developments widely used in machine tools, notably the lathe with its feedshaft and rack for moving the saddle. As the output of the ironmaster’s works, such as that of Abraham Darby at Coalbrookdale, increased tremendously by the use of coke in smelting (see p. Figure 7.5: A model of John Wilkinson’s cylinder boring mill of 1776. PART TWO: POWER AND ENGINEERING 398 153–4), the metal working machine tools had to keep pace and better cutting tools devised. The invention by Benjamin Huntsman of his process for making crucible steel in 1746 was of paramount importance, affecting the design of the feeds and speeds of machine tools to take advantage of the improved cutting capacity of this carbon steel and enable the machine tool makers to meet the demand for machined products. The workshops of Henry Maudslay were outstanding in this respect, producing general machine tools, including lathes based on his original design, and special purpose machines, such as the Portsmouth block-making machinery designed by Mark Isambard Brunel in 1800 and completed in 1810 to provide for the mass production of rigging blocks for the Royal Navy (see p. 30). Maudslay was also interested in many other types of machine. In 1805 and 1808 he patented calico printing machines, in 1806 a differential gear hoist with Bryan Donkin and a water aerator with Robert Dickinson, in 1824 a marine boiler water changer with Field, and in 1807 his famous Table Engine. Very many engines of this last type were constructed and were very successful in providing power in workshops. Marine engines were also constructed and the company became renowned for this, beginning in 1815 with the 12.7kW (17hp) engine for the Richmond, the first steam passenger vessel to ply on the Thames. Altogether the company produced engines for 45 ships in Maudslay’s lifetime. Mill machinery for Woolwich Arsenal, gun boring machines for Brazil, hydraulic presses, coin minting machines, pumping engines, foundry equipment and the shields and pumping equipment for Brunel’s Thames Tunnel in 1825 were all among the products of this company which became one of the greatest engineering businesses of the nineteenth century. In addition, and perhaps more importantly, it was the training ground for many of the important engineers of the day, including Maudslay’s partner Joshua Field, Richard Roberts, Joseph Clement, James Seaward, William Muir, Joseph Whitworth and James Nasmyth. Much of Maudslay’s success was due to his ideas of precision working and workshop management. He went to great lengths to produce accurate screw threads as the basis for precise division and measurement and developed the use of surface plates to obtain the true plane surfaces he regarded as essential in building his machines: these plates were placed on the fitters’ benches to test their work. Although Maudslay did not invent the micrometer (Gascoigne in 1638 and James Watt in 1772 (Figure 7.6) had made their devices), he constructed in about 1805 a bench micrometer called the Lord Chancellor which was the ultimate standard in his workshops. This instrument consists of a gunmetal bed carrying two anvils with end measuring faces. The movable anvil connects to a screw, cut to 100 threads per inch, through a slot to a split nut. Both anvils have bevel-edged slots through which the scale divisions on the bed can be read, and the milled head to turn the screw has 100 graduations, giving a movement of the measuring face of 0.0001 in ENGINEERING AND PRODUCTION 399 (0.00254mm) per division. There is also an adjustment to eliminate end play. Recent tests of the Lord Chancellor’s accuracy by the National Physical Laboratory justify the opinion that Maudslay was the first engineering metrologist of significance. Joseph Clement, who had followed Maudslay from the workshop of Joseph Bramah, was employed by him as chief draughtsman and later went on to improve the design of taps and dies in his own works where he specialized in fine mechanisms such as that in the calculating engines of Charles Babbage which he constructed from 1823. In 1827, Clement designed and made a facing lathe of such excellence that it won him the Gold Medal of the Royal Society of Arts. It had many features in advance of other lathe design and in particular it incorporated a mechanism to ensure a constant cutting speed across the face of the workpiece. He won many other awards for ingenious fitments for the lathe and in 1820 produced a planing machine in which the work was clamped on a reciprocating table passing beneath a cutting tool which could be moved horizontally and vertically. Matthew Murray, James Fox and Richard Roberts also produced planing machines at about this time, as this sort of machine was the key to satisfying the need for accurate plane surfaces in the building of lathes, special purpose machines and engines, the production of accurately guided crossheads being specially important for the development of steam engines in locomotive and marine applications. Clement’s most ingenious and lucrative machine design, however, was the immense planer he built in 1825, which employed a table moving in rollers on a masonry foundation to support the planing of workpieces 6 feet (1.82m) square. This was the only machine capable of handling work of this size for 10 years and at eighteen shillings per square foot of machining gave him a comfortable income. Figure 7.6: James Watt’s micrometer, 1772. PART TWO: POWER AND ENGINEERING 400 After two years in Maudslay’s works, Richard Roberts left in 1816 and set up his own works in Manchester where he produced in 1817 his planing machine (Figure 7.7) and his large industrial lathe which incorporated a back gear device to allow changes in spindle speed which is still in use today on simple lathes. The lathe also provided for a choice of relative speed between spindle and leadscrew, through a crown wheel arrangement, forward and reverse of the leadscrew and automatic stop. He also made many other machine tools and was the first to introduce plug and ring gauges to obtain uniformity in manufacture of textile machinery (see Chapter 17). His most important inventions were the automatic spinning mule and differential gear, in 1825, and his power loom of 1855 was the first effective weaving machine. Roberts, the most prolific and inventive engineer of his time, went on to develop steam locomotives; a steam road carriage including his differential gear in 1833; gas meters; clocks; and in 1847 the multiple punching machine, using the ‘Jacquard’ principle, designed to punch the rivet holes in Figure 7.7: Richard Roberts’ planing machine, 1817. ENGINEERING AND PRODUCTION 401 plates used in the construction of Robert Stephenson’s bridges at Conway and Menai Straits. James Nasmyth was appointed by Maudslay as his personal assistant in 1829 and left to start his own workshop when Maudslay died in 1831. He was enthralled by the ‘master’, wrote about his workshop and methods and followed these perfectionist practices in his own designs and workshops in Manchester. Here the firm of Nasmyth & Gaskell, later Nasmyth, Wilson & Co., manufactured locomotives and machine tools, many of the latter being exported to St Petersburg to equip the Russian locomotive works. Nasmyth introduced many ingenious devices to improve the operation of various machines but is principally famous for his invention of the steam hammer, c. 1839, which was produced to forge the 30in (7 5 cm) diameter paddle wheel shafts for the Great Britain, the second steamship designed and built by Isambard Kingdom Brunel. Finally screw propulsion was chosen, and the massive shaft not required, but the hammer revolutionized the production of heavy forgings elsewhere. The original invention was modified soon after to use steam on the down stroke of the hammer, making it double-acting; the automatic valve gear for regulating the stroke was invented in 1843 by Robert Wilson, one of Nasmyth’s partners. A working model of the hammer is shown in Figure 7.8. Nasmyth’s greatest commercial success was in the small shaping machine invented in 1836 which has remained in similar form in engineering workshops to this day. Of all the engineers who worked with Maudslay and emerged from that famous workshop to found their own, none adopted the ideas on standardization, accuracy and interchangeability, or developed them more effectively, than Joseph Whitworth. He worked for a time with Holtzapffel and then Clement before returning to Manchester to set up his own business in 1833, improving the design of machine tools, constructing them with greater precision using standard gauges based on accurate measuring machines and becoming the dominant figure in the world of machine tools of the nineteenth century. To provide for the accurate measurement required for the production of standard gauges used in manufacturing, Whitworth constructed two measuring machines: the first, the Workshop Measuring Machine, was designed to read to 0.0001in (0.00254mm) and the second, the Millionth Machine, to read to 0.000001 in (0.0000254mm). Both were comparators, set first to a standard and then on the gauge to be measured. A gravity ‘dropping piece’ was used to indicate the critical contact point. The Millionth Machine was exhibited at the Great Exhibition of 1851 along with a wide variety of his ‘self acting’ machine tools, including lathes; planing, drilling, boring and shaping machines; a wheel cutting and dividing engine; punching and shearing machines; and screw cutting equipment. Whitworth was a principal exponent of decimalization and standardization: the most famous example of his work, and that by which he is most remembered, is the standardization of screw . cutters and formed part of a series of machines for large-scale production of clocks. The shape of teeth for gearing had exercised the minds of mathematicians and clock and instrument makers since the. Clement designed and made a facing lathe of such excellence that it won him the Gold Medal of the Royal Society of Arts. It had many features in advance of other lathe design and in particular it incorporated. affecting the design of the feeds and speeds of machine tools to take advantage of the improved cutting capacity of this carbon steel and enable the machine tool makers to meet the demand for machined