UK 08The Lineage of British Gear Machines

Clock wheel-cutting engines and tooth-form theory (c. 1670–1850)

Cutting gear teeth by machine began with clockmaking. Clock wheels are small, have many teeth, and must be divided precisely into equal parts. So clockmakers used a dividing plate, which turned the wheel blank and stopped it at fixed angles, combined with a small rotating file (the forerunner of the milling cutter), in a wheel-cutting engine. According to Woodbury's History of the Gear-Cutting Machine (1958), the first British wheel-cutting engine on written record is one in Robert Hooke's diary, devised around 1670. The Science Museum in London holds a very similar engine from about 1672, which Woodbury writes is probably the oldest surviving wheel-cutting engine^[1]. The dividing plate, a screw to set the depth of cut, and a form cutter turned by a hand crank: the basics of the later gear cutting machine were already in place.

In the 18th century, Henry Hindley, a clockmaker in York, built a much sturdier wheel-cutting engine. The engineer John Smeaton saw it in the autumn of 1741 and later described it in a paper for the Royal Society. Besides a box frame and a micrometer to set the depth of cut, Woodbury writes, it had a scale of 60 divisions on the head of the worm, giving differential indexing that could divide tooth numbers not on the dividing plate. This was more than 150 years before the same idea appeared in the dividing heads of milling machines. The cutter could also be moved parallel to the blank's axis to cut the bottom of the tooth space flat^[1]. Samuel Rehé's wheel-cutting engine of 1783 had a much heavier frame and a dividing plate enlarged to 19 inches (about 480 mm), showing the transition from a clockmaker's tool to a machine for cutting machinery gears^[1].

The idea of hobbing also appeared in British instrument making of this period. In 1768 Jesse Ramsden, known for his dividing engines for engraving scales, cut gear teeth with a screw (worm) fitted with cutting edges. Woodbury regards this as the first example of cutting teeth with a hob. It was, however, one-off work for making instruments, not a production machine^[1].

Bringing tooth-form theory to the shop floor: Hawkins, Buchanan and Willis

For a long time the gears of large machinery were made of wood or cast iron, and tooth forms were set by the craftsman's eye. As steam engines and factory power transmission raised gear loads and speeds, a theory for setting tooth forms correctly became necessary. Woodbury names three men who "translated" the theories of French mathematicians for British engineers and the shop floor^[1].

The first, John Isaac Hawkins, translated Camus's treatise on tooth forms into English in 1806. The first edition contained errors by others and set off a controversy lasting 30 years, but in an appendix to the second edition of 1837 he explained that with involute teeth, gears of different sizes mesh at the same pitch and run correctly even if the center distance is slightly off. Woodbury writes that the background was the growing number of machines, like the change gears of screw-cutting lathes, that used many gears in changing combinations^[1]. The second, Robertson Buchanan, in his Essay on the Teeth of Wheels of 1808, gave tables and procedures that let even millwrights with no mathematical training lay out tooth forms with compasses and a rule^[1].

The third was Robert Willis of Cambridge. Willis placed gears within a system of mechanism and put the geometry of bevel and screw gears in order. Three things made a difference to real gears. First, he proposed a 14.5° pressure angle for involute teeth (an angle whose sine is almost exactly 1/4, later carried over into the Brown & Sharpe system). Next, he gave the name diametral pitch (teeth per inch of diameter) to the way of stating tooth size used in Manchester, and published a table comparing it with circular pitch. And in 1838 he devised and named the odontograph, a graduated rule for drawing tooth forms approximated by two circular arcs, and published how to make it along with tables^[1]. William Fairbairn's Treatise on Mills and Millwork (1864) explained Willis's odontograph with illustrations and noted that it was available as a graduated card or wooden scale from Holtzapffel in London (a workshop known for ornamental lathes)^[3]. If the correct tooth form can be drawn on the drawing board, form cutters and patterns of that shape can be made. Theory had become a tool of the factory.

Engineers' gear cutting machines: Fox, Roberts, Bodmer and Whitworth

From the 1820s to the 1840s, engineers' gear cutting machines appeared: not clockmakers' tools but machines for cutting the large gears of factories. According to Woodbury, around 1820 James White showed in his book a wheel-cutting engine that could cut helical gears and spiral bevel gears, and before 1833 James Fox of Derby was using a gear cutter in which the blank was mounted upright on a sturdy lathe-like bed and divided with an indexing cylinder and screw (mainly for cutting patterns for cast gears)^[1]. In Manchester, a gear cutting machine of about 1824–34 attributed to Richard Roberts indexed the number of teeth with change gears and could tilt the cutter head to cut bevel gears as well. This machine was reportedly still in use in a British factory in 1908^[1].

John George Bodmer, Swiss-born and with a works in Manchester, showed in British patent No. 8,070 of May 29, 1839 a gear cutting machine that cut spur gears with a form milling cutter and had attachments for internal gears, bevel gears, worm wheels and racks. His cutters for metal gears were built up in segments to make them easier to harden. Woodbury writes that resharpening form cutters took much labor and cost^[1][2].

And then there is Joseph Whitworth. Whitworth is known for his standards of flat surfaces and screw threads (Chapter 1), but he was also in the lead with gear cutting machines. Woodbury regards Whitworth's machine of 1834–44 as the first gear cutting machine to combine an involute form cutter, indexing by gears, and a power-driven cutter turned by belt and worm, and says a self-acting feed version had been built by 1851^[1][2]. Further, in British patent No. 6,850 of June 11, 1835, he showed a machine that cut worm wheels by turning the blank and the hob together in an exact ratio through a gear train. Woodbury places this as the first use of hobbing in a production machine and the first machine to generate involute teeth (it could cut only helical gears and worm wheels)^[1]. The core idea of the later hobbing machine, "synchronizing the rotation of cutter and blank through gears," appears here.

What it means on the shop floor. Worm wheels are still cut today with a hob of the same form as the mating worm. Keeping the axes of worm and wheel at right angles and turning the hob and blank in a fixed ratio is the same idea as Whitworth's patent. The "D.P. (diametral pitch)" and 14.5° pressure angle that appear on old British drawings are relics of the British and American systems going back to Willis, and such gears will not mesh with today's gears based on module and a 20° pressure angle.

Gear works and gear-cutting machine makers (1851–1906)

By the middle of the 19th century, British gear cutting machines had become production machines. Woodbury cites the 1851 machine of Shepherd, Hill and Spink of Leeds as an example. The cutter was still driven by rope, but the machine had self-acting feed and indexed with change gears^[1]. Woodbury sums up that by 1850 every method of forming teeth (form cutter, template and generating) had become a production machine, and British machine designers (ahead of the Americans) could use accurately cut spur, bevel and worm gears in quantity^[1].

On December 6, 1856, Christian Schiele showed in British patent No. 2,896 a machine that cut spur gears, helical gears and worm wheels by turning the blank and hob in the correct ratio through gears. Whereas Whitworth's machine could cut only worm wheels, this one was new in placing the hob at right angles to the blank's axis so that it could cut spur gears too, and Woodbury treats it as the beginning of the hobbing machine type. It is not known, however, whether it was actually used, and hobbing machines did not spread until about 40 years later^[1][2]. Woodbury attributes this to three things: tooth forms were still mainly cycloidal, which made hobs hard to make; demand for mass production had not yet come; and it was difficult to finish a hob to the correct form after hardening^[1].

David Brown: from pattern shop to gear works

David Brown, which would become Britain's largest gear maker, began in 1860 in Huddersfield (Yorkshire) as a pattern maker. Its specialty was patterns for cast gears. According to The Engineer, which reported on the works in 1935, when the sons joined, the firm began making the gears themselves, installed machines to divide the tooth spacing accurately, and studied tooth forms that were easy to make. When its first gear cutting machine arrived in 1890, it became clear that gears with machined teeth outperformed cast gears, and the gear shop came to outgrow the pattern shop^[6][7]. In 1902 the firm built the new Park Works at Lockwood, and by 1903 it was making standardized worm reduction units. From about 1906 it concentrated on worm gears to meet demand from cars and trucks^[6].

Gear-cutting machine makers in Manchester and Rochdale

On the machine-building side, Manchester companies stood out. According to Woodbury, in 1877 automatic gear cutters for production were put on the market at the same time by three firms in Britain and America: Brown & Sharpe and Gould & Eberhardt in the U.S., and Craven Brothers in Britain^[1][9]. Once a blank was mounted, the machine cut every tooth to the last and stopped on its own, so one person could tend several machines (for the American side of the story, see the chapter on American gear machines). At the 1900 Paris Exposition, Smith & Coventry of Manchester showed a bevel gear cutting machine that cut both sides of a tooth with two tools^[1].

Rochdale's John Holroyd & Co. began, according to the company's history, in 1860 in Manchester as a shop for machine tools and textile machinery, and later moved to Rochdale (Milnrow)^[8]. In 1897 it took out a patent for a machine for thread milling, cutting threads with a milling cutter instead of a lathe tool. Steeds (1969) says that Liebert, the works manager, took out the patent in 1897 and Holroyd built the machine. In the U.S., Henry Liebert's "Machine for Milling Screws" was granted in 1900^[8][2][10]. Threads, worms and hobs all belong to the same family of helices, and Holroyd extended this technology to worm gears and hobbing machines. Steeds's book illustrates a Holroyd hobbing machine of 1904, and in 1906 Engineering carried a photo feature on the Holroyd hobbing machine shown at the machinery exhibition at Olympia in London^[2][13]. The same article named gear hobbing machines and cam cutting machines as new machines born of the growth of the motor industry^[13].

In automobile gears, the work of Frederick W. Lanchester should not be overlooked. For the rear axle of his own car, Lanchester used an hour-glass worm that wrapped around the wheel, and in 1896 he designed a hobbing machine to make it^[9][2]. Worm-drive rear axles later became one of David Brown's specialties.

What it means on the shop floor. Many British gear works started out as pattern shops, and at the end of the 19th century they switched from the thinking of the pattern and cast-gear era (draw the tooth form and make a pattern) to the era of cutting teeth on gear cutting machines. When repairing an old British machine, checking whether its gears are as-cast or have cut teeth gives you an idea of when it was built.

Turbine reduction gears and double helical gears (1897–1918)

In the early 20th century, the most demanding requirement placed on British gear making was reduction gearing for steam turbines. Turbines run best at several thousand rpm, but a ship's propeller does not push water efficiently unless it turns at around 100 rpm. Reducing that difference with gears means large gears, high pitch-line speeds and very large transmitted power. Even small tooth errors show up as vibration, noise and tooth damage.

Parsons and the Vespasian

Charles Parsons, who made the steam turbine ship a practical reality, described in his Rede lecture of 1911 how in 1897 he fitted a 22-foot (about 6.7 m) launch with a 20,000 rpm turbine reduced through 14:1 helical gears, presenting it as the first geared turbine vessel^[11]. Full-scale trials took place on the cargo ship Vespasian (4,350 tons), bought in 1908. The reciprocating engine was removed and replaced with two turbines, high-pressure and low-pressure, each driving a pinion at 1,400 rpm meshing with a large gear on the propeller shaft turning at 70 rpm. Coal savings were 15%, rising to 22% after the propeller was modified^[11]. According to Parsons's 1913 paper, geared turbines then spread to cargo ships, cross-Channel steamers and warships, exceeding 120,000 horsepower including those under construction^[14].

Muir's hobbing machines, and why gears sing

The gears were cut on hobbing machines from William Muir & Co. of Manchester. According to Parsons's 1913 paper, to verify the accuracy requirements for the teeth himself, in 1910 he installed two Muir hobbing machines at the works of the Parsons Marine Steam Turbine Company, and two of the same type at C. A. Parsons & Co., which made gears for generators and rolling mills. By 1913 the machines had cut gears for about 50,000 horsepower in all^[14]. According to a 1960 obituary in Electrical Review, it was W. Owen, Muir's technical director, who worked with Parsons on the first turbine-gear hobbing machine and designed it^[17].

But the gears that came off the machines sang. Parsons hung a microphone over the gearbox and analyzed the sound with an oscillograph. The pitch of the sound turned out to be 160 times the gear's rotational speed, the same period as the 160 teeth of the master worm wheel that turned the hobbing machine's table. Small errors in the master worm wheel were copied onto the cut gear with the same period, and that was what made the noise. When measured, the errors were indeed spaced with the same period as the teeth of the master wheel^[14]. At first the noise was eased by supporting the pinion bearings on springs, but Parsons considered this an incomplete remedy and looked for a way to improve the accuracy of the teeth themselves.

The creep mechanism (1912)

The British patent filed by Parsons, Carnegie and Cook on December 20, 1912 (published December 1913) was the creep mechanism^[20]. A second table is mounted on top of the table carrying the master worm wheel, and the upper table carrying the blank is geared to "creep" ahead of the lower table by 1%. The lower table is turned 1% slower, so the blank's rotation stays as before. In this way the master wheel's errors, instead of lining up along planes through the gear's axis, are scattered around the gear in a gentle helix. Because the hob cuts at a slightly shifted position on each revolution of the blank, the peaks of error are averaged out as cut overlaps cut; by Parsons's account, the remaining error was about one-fifth of the original^[14]. Steeds writes that this "creep" method was developed by Parsons and his colleagues shortly after this period^[2]. The reduction gears of the liner Queen Mary of 1936 were also cut on hobbing machines with the creep mechanism^[30].

Cutting double helical gears: Sunderland and Sykes

Turbine reduction gears often used double helical (herringbone) gears. Helical gears mesh smoothly but produce an axial thrust. Placing left- and right-hand helices side by side cancels that thrust. But when a double helical gear is hobbed, the hob needs room to run out, so a center groove is required between the two halves, making the gear wider and heavier. Sunderland and Sykes devised machines that did away with this groove.

Sam Sunderland (whose business later passed to the Keighley Gear Company) took out British patents for a machine cutting helical gears and worm wheels in 1903 and for a bevel gear generator in 1907, and then on October 8, 1908 filed a patent for a gear planer that generates spur gears with a multi-tooth cutter in the form of a rack (US patent 948,830 followed in 1910)^[12][15]. The cutter reciprocates while the blank is rolled and the cutter fed. According to Steeds, the clever part was a "step-back" motion that returned the cutter by a few teeth so that it did not have to be as long as the full circumference of the gear, and from about 1909 Shipley's J. Parkinson & Son built it^[2]. In 1912 he also patented cutting double helical gears without a center groove using a rack cutter with its teeth inclined at the helix angle^[19]. In 1917 Engineering explained that because the cutting edges are constantly changing, there is less heat and wear than with methods that cut one tooth at a time^[16]. Woodbury, too, lists the Sunderland alongside the Fellows gear shaper as a machine that cuts several teeth at once^[1].

William Edwin Sykes filed a British patent on July 17, 1911 for a method of cutting double helical gears with two gear-shaped cutters. The cutters reciprocate while being twisted by rifle bars (bars with helical grooves), rolling together with the blank to generate the left- and right-hand helical tooth forms^[18]. In 1913 he also filed an improvement in which two cutters mounted on one ram cut alternately^[21]. In 1916 Engineering described the Sykes machine built and used in its own works by Power Plant Company of West Drayton. It developed the principle of the American Fellows gear shaper: the left and right cutters reciprocate by crank and cut right up to the center line, so the central relief groove needed for hobbed double helical gears is not required. It reportedly finished a gear in about half the time of a hobbing machine and one-twentieth the time of end milling^[23]. In 1928 the company completed a large Sykes-type machine able to cut turbine gears up to 9 ft 6 in (about 2.9 m) in diameter and 30 in (about 760 mm) wide^[27].

Standards and the beginnings of gear grinding

Around the same time, work on gear standards also began across national borders. In July 1910 the American Society of Mechanical Engineers (ASME) and the British Institution of Mechanical Engineers (IMechE) held a joint meeting in Birmingham to discuss a system of interchangeable involute gears. No conclusion was reached, but Woodbury writes that it set the trend toward the spread of the Brown & Sharpe system^[1]. In finishing hardened gears, in 1908 Thomas Humpage presented to the Institution of Mechanical Engineers experiments in fitting a hobbing machine with a worm of corundum (an abrasive) to finish hardened automobile gears. Woodbury says the first attempt to grind hardened gears was by Humpage in Britain^[1]. It is the same idea as today's continuous generating grinding of gears with a threaded wheel; the history of grinding machines is covered in Chapter 7: Grinders.

What it means on the shop floor. When a gear cut on a hobbing machine produces noise at a fixed period (as many peaks per gear revolution as there are teeth on the table's worm wheel), suspect errors in the worm and wheel driving the table. It is the same phenomenon that Parsons and Couling (see below) tracked down. Today's CNC hobbing machines suppress it by turning the table with a high-precision worm or a direct drive and compensating for errors.

Standards, research and the two world wars (1919–1945)

Double helical gear machines go to America

Soon after the end of World War I, David Brown bought Keighley Gear Company (successor to Sam Sunderland's business) and further enlarged the works it had expanded during the war^[6]. The Sykes machine crossed the Atlantic. According to an American trade journal of November 1925, Farrel Foundry & Machine of Buffalo had bought the US and Canadian patents for the Sykes gear cutter three years earlier, shipped four machines from Britain and begun making "Sykes continuous herringbone gears." As demand grew, the machines in Buffalo numbered 15, and gear companies on the West Coast and in Chicago also bought complete sets of machines^[24]. A British-born gear cutting machine thus spread to American shops making heavy gears for steel, paper and other industries (the chapter on American gear machines). Sunderland's planers also grew larger: in 1931 The Engineer introduced a Sunderland gear planer for gears up to 15 ft (about 4.6 m) in diameter, the largest machine for generating spur gears at the time^[29].

Worm gears: Holroyd and David Brown

Between the wars, British gear companies made their names with worm gears. Holroyd showed a worm-wheel hobbing machine and a worm grinding machine at the 1924 machinery exhibition^[25], and according to the company's history, in 1931 its worm gear recorded an efficiency of 98.2% in tests at the National Physical Laboratory (NPL)^[8]. Worm gears are often thought of as slipping a lot and having low efficiency, but this showed that by refining the tooth form, materials (phosphor bronze) and finish, efficiency close to that of spur gears could be achieved. At David Brown, the engineer H. E. Merritt left a worm gear patent filed in Britain in 1930 (granted in the U.S. in 1934)^[28].

Visiting David Brown's Park Works in 1935, The Engineer described a works of about 2,000 people. Small spur and helical gears were finished on Maag gear grinding machines, spiral bevel gears were cut on rows of Gleason machines, double helical gears were generated by shaping or planing, and the triple helical gears of mine winders were cut with end mills. The firm even cast its own phosphor bronze for worm wheels. Before World War I it had also joined with Timken of the U.S. to form a company making its patented worm-drive rear axles in America^[6]. According to Fraser's biography of Harry Ferguson, it was David Brown that made the gears, transmission and steering for Ferguson's new tractor, and that led to the company's own tractor business^[49].

British Standard (BS) gear standards

British gear standards began with BS 235 "Gears for Traction" (gears for tramcars and the like) in 1927. BS 436 of 1932, "Machine-Cut Gears: Helical and Straight Spur" (spur and helical gears, revised 1940), was followed by BS 545 (bevel gears) in 1934, BS 721 (worm gears) in 1937 and BS 978 (gears for instruments and clocks) in 1941^[26]. As Merritt later wrote, BS 436, 545 and 721 aimed to be "design guides" covering not only dimensional interchangeability but also design, accuracy and permissible loads^[26]. As standards from the inch era, they cannot be swapped directly with gears to Japan's JIS (module, 20° pressure angle).

Merritt's Gears and tank transmissions

David Brown engineer Henry Edward Merritt published the leading British textbook of gear engineering, Gears, with Pitman in 1942^[32][33]. It covered design, manufacture and testing in one volume; a second edition followed in 1946 and a third in 1954. Merritt also made his name with tank transmissions. His British patent application of December 1939 for the steering gear of tracked vehicles combined the gearbox with a differential to turn the vehicle by changing the speeds of the left and right tracks through gears^[31]. A 1943 British report, in the course of examining the German Tiger tank, noted that Merritt-type differential steering was used in the British Churchill, Cromwell and Centaur tanks^[34]. The ability to make many gears accurately and in quantity underpinned wartime equipment.

The cause of noise: the worm wheel again (1943)

In January 1943, in the middle of the war, S. A. Couling of British Thomson-Houston (BTH) in Rugby presented research on turbo-generator reduction gears to the Institution of Mechanical Engineers. BTH cut its gears on American-made hobbing machines without the creep mechanism, but a 500 kW, 8,000 rpm gear gave off a "whistling" noise. Remedies such as filling with lead or adding a flywheel did not work; he found the cause when the noise frequency (1,340 cycles per second) turned out to equal the speed of the low-speed shaft multiplied by the 120 teeth of the hobbing machine's master worm wheel. Couling made a new 360-tooth master wheel and improved its accuracy by recutting it with the teeth shifted one pitch at a time, pushing the noise up to an inaudible pitch^[36]. Parsons's discovery of 30 years earlier had been confirmed once again.

★From turbine-gear hobbing machines to today (1946–)

BS 1498 and the Grade A hobbing machine

After the war, Britain made a standard for the hobbing machines that cut turbine gears. According to The Engineer in 1952, the experience built up over two world wars was summed up in BS 1498 of 1948 (hobbing machines for turbine and similar gears). It was drawn up at the Admiralty's request by the National Physical Laboratory (NPL), the classification society Lloyd's Register, and makers and users of hobbing machines. In it, Grade B for ordinary production and, for gears transmitting large loads at high pitch-line speeds, Grade A are defined^[39].

The machines that met this standard were built by David Brown Machine Tools (formerly Muir Machine Tools) of Manchester. Muir, which had built the first turbine-gear hobbing machine with Parsons, had come under David Brown in December 1944^[5]. According to the journal, the company had long built both creep-type and solid-table hobbing machines (the latter making the master wheel itself precise, without creep). The indexing worm wheels of its master machines had reduced their errors each time they were remade from parent to child, and were said to be “the great-grandfather of the indexing worm wheels of almost every turbine-gear hobbing machine now in existence.” The article also reported the view that, as accuracy improved, the creep mechanism was becoming unnecessary. The first machine to meet Grade A was delivered in 1948 to the Cammell Laird shipyard in Birkenhead; it had separate indexing worm wheels for roughing and finishing, and two independent power supplies so that it could keep cutting through a power cut^[39]. Hobbing machines were also made after the war by Craven Brothers, where W. Owen, formerly of Muir, was chief designer until 1955^[17].

Research organizations and standards

The Admiralty and Vickers formed a gear research association (the Admiralty-Vickers Gearing Research Association), which issued Report No. 1 in 1949 and later also compiled guidance on installing and readjusting hobbing machines^[40]. After the war, the government's Department of Scientific and Industrial Research (DSIR) set up the Mechanical Engineering Research Laboratory (MERL) at East Kilbride (near Glasgow), which in 1959 was renamed the National Engineering Laboratory (NEL). Gears and machine tools, and the measurement of tooth errors, were among the pillars of its research^[41][42]. In standards, BS 1807 (accuracy of turbine and similar gears) of 1952 was followed in 1953–56 by standards for shaving cutters, hobs, form cutters, terminology and rack-type cutters. Merritt, on the other hand, argued in The Engineer in 1956 that revision of BS 436, 545 and 721, which dealt with design and permissible loads, had fallen behind^[26].

Holroyd and rotors

After the war, Holroyd extended its technology for cutting helical forms, honed on threads and worms, to the rotors (male and female screw-shaped rotors) of screw compressors. According to the company's history, it set up Holroyd Precision Rotors, a contract machining division, in 1953, and received the Queen's Award for technological innovation in 1967, again in 1993 for its rotor cutter grinding machine, and in 2004 for its thread and gear grinding technology^[8]. Rotor profiles are far more complex than gear teeth, but generating and form grinding, and the skills of making tool forms accurately, are shared with gear grinding machines.

British gear machines today

Gleason of the U.S. built a tool plant in Plymouth, England, in 1966^[45]. In 2010 Holroyd joined the group of China's Chongqing Machinery & Electric (CQME), and as PTG (Precision Technologies Group) Holroyd it makes rotor milling and grinding machines, gear grinders, worm grinders and friction stir welding machines in Rochdale^[8]. In 2016 David Brown combined with Santasalo of Finland to become David Brown Santasalo. The company makes industrial gear units and has also taken over servicing of units from old gear brands such as Power Plant Gears, Sykes, BTH and Radicon^[7][46]. Today's gear machine and tool makers are listed in Makers of gear cutting tools and gear machines, and how to use each tool is covered on the hob, pinion cutter, and shaving cutter pages.

What it means on the shop floor. When repairing or remaking large turbine gears or the double helical gears of rolling mills, the machines you can use depend on whether the original gear was "hobbed (with a center groove)" or "Sykes or Sunderland type (no groove, the two halves meeting)." Grooveless double helical gears are still usually cut on machines that cut each side with pinion cutters, or on 5-axis machines. Old British gearboxes may have been made to Grade A/B (BS 1498) or BS 436 grades, so check which edition of the standard the drawing uses.

Links with Japan

American and German machines played a large part in the beginnings of gear cutting in Japan (see the America, Germany chapters). British machines played a part too. According to Toshio Aida's Haguruma no gijutsushi (History of gear technology, 1970), in 1914 a Japanese gear-cutting specialist shop installed a British-made hobbing machine, said to be the first foreign-made hobbing machine installed by a gear-cutting contractor^[22]. It came eight years after the German Pfauter hobbing machine of 1906 (at a shipyard and a navy arsenal) said to be Japan's first (see the Japanese Archive, Chapter 4 timeline).

There is also a British link in ships' turbine gears. According to Aida, by the end of the Taisho era (mid-1920s) Japan had more or less completed domestic production of various hobbing machines, but foreign makers supplied the large gear cutting machines for cutting the main turbine gears of warships and merchant ships: Britain's William Muir, America's Westinghouse and others^[22]. Muir, as we saw in this chapter, was the company that built turbine-gear hobbing machines for Parsons in 1910^[14]. Machines for cutting large, precise gears such as turbine gears were among the last to be built domestically, which shows that British experience also found its way into Japanese shipbuilding.

British gear standards and textbooks were also read by Japanese engineers in the era of inch gears. After the war, however, Japan adopted the module and 20° pressure angle system in JIS, so its tooth forms differ from British D.P., 14.5° gears. When remaking a gear for an old British machine, the starting point is to identify the tooth-form system first (see "Gear study", section on tooth forms and standards).

FAQ

Was the idea of the hobbing machine born in Britain?

Cutting teeth with a hob is first recorded in Jesse Ramsden's instrument making of 1768. Machines that turn the blank and hob in sync through a gear train appear in Whitworth's British patent of 1835 (for worm wheels) and Schiele's British patent of 1856 (for spur and helical gears too). But the basics of the modern hobbing machine, which tilts the hob axis by the helix angle and cuts helical gears through a differential, were put together by Pfauter of Germany (1897), and the machine came into wide use only in the 20th century.

What is Parsons's creep mechanism?

A device to solve the problem of turbine reduction gears singing because errors in the master worm wheel that turns the hobbing machine's table were copied onto the cut gear with the same period. Parsons, Carnegie and Cook filed a patent for it in 1912. The table carrying the blank is turned so that it shifts by about 1% relative to the master wheel each revolution, scattering the errors around the gear in a helix and eliminating the periodic error (the noise). After the war the accuracy of master wheels themselves improved, and hobbing machines without creep became more common.

How were double helical gears without a center groove cut?

Two methods were born in Britain. Sam Sunderland's gear planer (patented 1908, built by J. Parkinson & Son) used a multi-tooth rack cutter, and W. E. Sykes's machine (patented 1911, built by Power Plant Co.) used two gear-shaped cutters; both cut the left and right helices right up to the center line. Sykes's US patents were bought by Farrel of the U.S. around 1922, and the method spread in America too.

When were British gear standards (BS 436 and others) issued?

The first was BS 235 (gears for tramcars and the like) in 1927; BS 436 for spur and helical gears came in 1932 (revised 1940), BS 545 for bevel gears in 1934, BS 721 for worm gears in 1937 and BS 978 for instrument and clock gears in 1941. BS 1498, the standard for hobbing machines for turbine gears, was drawn up in 1948 (according to Merritt 1956 and The Engineer 1952).