GERMANY 08The Lineage of German Gear Machines

The birth of the hobbing machine and the beginnings of the gear companies (1887–1918)

What was new about hobbing?

In the 19th century, gears were mainly cut with a form milling cutter shaped like the tooth space: cut one space, turn the blank by one tooth (index), and repeat. This meant changing the cutter every time the number of teeth or the module changed, and the machine stopped at every indexing. A hob is a cutter made by cutting gashes in a screw (worm) to form cutting edges. If hob and blank are kept turning at a fixed ratio, so that the blank turns by one tooth for each revolution of the hob, the hob's teeth strike the blank one after another like a rack, and the involute profile forms naturally by “rolling.” Its strengths were that one hob could cut gears with different numbers of teeth for the same module, and that it cut continuously without stopping^[4].

The idea itself existed in 19th-century Britain and America, and in Germany too, Juengst in 1893 and J. E. Reinecker of Chemnitz in 1894 brought out hobbing machines for spur gears. But all were early types in which the blank axis and the hob feed were horizontal^[4]. Chief designer at Reinecker from 1887 was the man who would become the father of the hobbing machine, Robert Hermann Pfauter (1854–1914)^[1].

Pfauter's patent: cutting helical gears with a differential

On September 1, 1897, Pfauter filed a German patent application for a method and machine for cutting helical gears with a hob (DRP 112082; the NDB, going by the year it was granted, calls it “the 1900 patent”)^[7][1]. In a helical gear the teeth shift sideways as the hob moves down across the face width, so the blank's rotation has to be advanced or retarded little by little in step with the feed. Pfauter's key idea was to add this “plus and minus” to the rotation of hob and blank through a differential gear. The patent claims describe a device that adds circumferential motion from the differential to the straight axial feed, feeding the rotation of the feed screw into the differential to advance or retard the hob drive^[7]. US Patent 640,728, granted in 1900, likewise explains that turning the cutter slide to change its angle lets the machine cut spur gears too, and that adding extra rotation in step with the feed produces helical teeth^[11].

The American historian Woodbury judged that Pfauter's machine, which could tilt the hob axis to any angle relative to the gear axis and cut even helical gears with a differential, brought together the basic elements of the hobbing machine^[4]. In shop-floor terms, the change gears for indexing and the change gears for the helix angle could now be set up separately, so there was no longer any need to rebuild the whole indexing gear train every time the helix angle changed. This is also why Japanese hobbing machines “with differential” were so prized (Japanese Archive, Chapter 4).

In 1900 Pfauter founded his own company in Chemnitz and became a specialist maker of hobbing machines^[8][1]. According to the NDB, it built about 2,000 machines in 1905–13, and they sold well in America too (the Gleason-Pfauter history places the 2,000th machine in 1908–14)^[1][8]. When Pfauter died in 1914, his wife Clara took over the company, and their sons widened the range from machines for small gears to machines for large ones^[1]. According to a British trade journal of 1961, Pfauter celebrated its 10,000th machine in 1936 and had built 17,000 by the end of the war in 1945^[28].

Shaping, grinding and shaving companies are born

Around the same time, one company after another was born that would later carry German gear machinery. In Ettlingen, the industrialist Wilhelm Lorenz bought a factory in 1890 and in 1893 named it Maschinenfabrik Lorenz. It became a leading name in the gear shaping machine (gear shaper), which cuts teeth by moving a gear-shaped cutter up and down, and in gear cutting tools^[2][3]. A 1909 American book shows a Lorenz gear hobbing machine, and in 1934 a Moscow factory was building machines modeled on the Lorenz gear shaper^[14][27]. In München, Carl Hurth opened a machine works in 1896 and built his first gear cutting machine himself to keep up the quality of his own gears^[5][6]. In Berlin in 1898, Deutsche Niles-Werke was founded to use the technology of Niles Tool Works of the US. At first it built large lathes and planers; it moved into gear grinding machines in the 1930s^[9].

Machines for grinding hardened gears also appeared early in Chemnitz. The 1909 American book Gear-Cutting Machinery describes Reinecker's grinder for finishing hardened automobile gears. It used both sides of a wheel dressed to the shape of a rack tooth and moved the gear as if rolling it on an imaginary rack, grinding one space at a time; it could grind gears up to about 11 inches (about 280 mm) in diameter and 2 inches in face width^[14]. Woodbury regards it as the first machine to grind hardened automobile gears^[4].

The 1910 skiving patent

The most forward-looking patent of this period was German Patent 243514, effective from March 1, 1910. The method crossed the axes of a gear-shaped cutter (with cutting edges on the end faces of its teeth) and the blank at an angle and turned both continuously; because the axes cross, the edges slide over the blank, and that sliding becomes the cutting motion. The specification noted that on a shaper the return stroke of each reciprocation of the cutter is wasted, and that hobbing cuts without stopping but cannot be used for internal gears, and stated that this method could cut internal gears without stopping, which it presented as its advantage^[15]. It is exactly today's skiving (Wälzschälen, power skiving).

Papers and makers call this “Wilhelm von Pittler's patent”^[16][17]. Pittler was the inventor who founded a turret lathe maker in Leipzig; he moved to London in 1909 and died in September 1910^[18]. In the patent office's bibliographic data the applicant is given only as George Adams of London, but the cover of the specification published in February 1912 names “George Adams of London and the legal successors of Wilhelm von Pittler, deceased, of London”^[15]. The idea was right, but it took about 100 years before the method was used in factories (Restructuring, dry cutting, skiving).

Maag and ZF: gear companies spread the machines

In neighboring Switzerland, Max Maag founded a gear company in Zürich in 1913. Maag devised his own tooth form that strengthened the tooth root by changing how the cutter was positioned (profile shift), and brought out a gear planer that cut with a rack-shaped cutter and, at the request of the Belgian car maker Minerva, a spur gear grinding machine^[19][20]. Its ties with Germany were strong: in 1915 Maag licensed Thyssen of Mülheim and others, and in the same year, together with the airship maker Zeppelin, founded in Friedrichshafen Zahnradfabrik Friedrichshafen (ZF). ZF's first head, Alfred von Soden-Fraunhofen, was an engineer troubled by the noisy gears of airship engines^[23][19]. A company that uses gears buys the machines and the tooth form together in order to make precise gears: this pattern led on to later automotive transmission making.

On the tool side, Klingelnberg, a tool merchant in Remscheid, began making gear hobs in 1914–16 and moved its works to Hückeswagen in 1916^[21][22]. During World War I, when the US became an enemy, Deutsche Niles-Werke dropped the American company's name and called itself Maschinenfabrik Oberschöneweide (returning to the original name in 1920)^[9].

Bevel gears, gear grinding and climb hobbing (1918–1945)

Klingelnberg's Palloid: cutting bevel gears with a conical hob

For the car rear-axle spiral bevel gears, Gleason of the US had brought out a machine in 1913 that cut one space at a time with a cutter head, and dominated the market (the chapter on American gear machines). In 1922 Klingelnberg bought the patents of Schicht and Preis for cutting bevel gears with a hob. According to the NDB, unexpected mathematical and manufacturing difficulties arose, which Klingelnberg and his engineers solved at great expense^[21]. This became the Palloid method, and the company history says it began building Palloid gear cutting machines in 1922^[22].

The first bevel gear hobbing machine, the FK 150, built at the Hückeswagen works in 1923, had a tool head that could be set to various cone angles and used a hob with a 40° cone angle^[22]. Because the blank keeps turning while the conical hob (a cutter modeled on a conical worm) rotates, there is no stopping time for indexing one space at a time as in Gleason's method. The tooth trace also differs: Gleason gears have a circular arc, Palloid gears a nearly involute curve^[47]. The NDB writes that one of the earliest machines of this kind is in the Deutsches Museum in München^[21]. In 1935 Klingelnberg also brought out a pendulum-type universal gear tester^[22], becoming a company that both “cuts” and “measures” gears.

After the war, a method was added that cut bevel gears with a cutter head (a circular cutter) but without indexing. By 1950 Oerlikon of Switzerland had brought out the Spiromatic No. 2, which linked three motions, cutter-head rotation, blank rotation and generating roll, to cut continuously^[35], and Klingelnberg also built machines using the Cyclo-Palloid method, which cuts with a cutter head. A British technical journal of 1957 described the FK 41 for small bevel gears (an improvement on the earlier FK 40)^[46]. Cyclo-Palloid and Oerlikon tooth traces are curves called extended epicycloids^[47].

Gear grinding machines: Niles's discontinuous generating grinding

In the 1920s and 30s, grinding became indispensable for automobile and aircraft engine gears, to remove distortion after hardening and make them run quietly. In 1925 ZF launched a transmission common to cars, trucks and buses, and in 1926, for quiet gears, bought a license from Minerva of Belgium for its technology for grinding helical gears^[23].

At Niles in Berlin, the engineer Paul Uhlich began preparatory work around 1926 and in 1931 built a gear grinding machine using his own discontinuous generating grinding (Teilwälzschleifen) method, protecting it with patents. The KAPP NILES timeline says that demand for precision gears was growing in automobiles, aircraft engines and machinery, and the existing methods were no longer enough^[9]. In discontinuous generating grinding, the gear is rolled against a wheel shaped like a rack tooth to grind both flanks of one tooth space, then indexed by one tooth to the next space. It is called “discontinuous” (Teil-, partial) in contrast with methods that grind all the teeth continuously (continuous generating grinding, which comes later). Niles brought out its 500th grinder (RS type) within 10 years, but from the end of 1941 it was on 60-hour weeks of war production, and forced laborers were made to work there too^[9].

Pfauter's climb hobbing

On the hobbing side, in 1938–39 Pfauter commercialized climb hobbing (hobbing that cuts in the same direction as the feed) and brought out the first automatic hobbing machine and a motorized hob head^[8]. A postwar Soviet technical journal described how before the war Pfauter had fitted its large RS machines for gears of 350–2,500 mm diameter with devices for hobbing in the feed direction (including hydraulic counterbalancing), explaining that the machines ran quietly with little vibration, the tools lasted longer and cutting speeds could be raised^[29]. In ordinary (conventional) hobbing the tooth enters at the thin end of the chip, so the edge rubs for a long time; in climb hobbing it enters at the thick end, reducing wear and heat. In exchange, a counterbalancing device was needed so that backlash in the feed screw would not let the tool be pulled in. That climb hobbing can be routinely selected on today's hobbing machines goes back to the ideas of this period. In 1927 an article explaining how Pfauter's method came about also appeared in the VDI journal^[4][1].

The beginnings of research on gear strength, and the war

Not only how to make gears but also the calculations for those who use them began to be studied at universities. Gustav Niemann (1899–1982) became professor of machine elements at TH Braunschweig in 1934, studied the rolling contact pressure and life of tooth flanks on a roller testing machine, and in 1942 presented a theory of hydrodynamic lubrication of worm gears and the Cavex worm with a concave circular-arc tooth profile^[25][26]. In 1939 ZF switched its plants to war production^[23]. By the end of the war, Niles's large works in Berlin-Weißensee was a burnt-out ruin^[9].

Gear machines divided between East and West (1945–1974)

Pfauter splits into Chemnitz in the East and Ludwigsburg in the West

With defeat, Germany's gear machine centers were divided between East and West. In Chemnitz, which fell in the Soviet zone of occupation, most of the Pfauter works' equipment was dismantled and carried off, and the works was seized^[8][1]. A 1952 US intelligence report also says that many machine tool plants in the Soviet zone, after their most valuable machines were taken as reparations, reassembled machines from leftover parts and reopened in 1947–48 (the report wrongly describes Pfauter as a Leipzig company)^[30].

Many of the Pfauter family and engineers left Chemnitz, moved first to Berlin and made a new start in the West. According to a British trade journal of 1961, in June 1947 Opel lent them a small bomb-damaged building in Rüsselsheim; in 1948 Eickhoff of Bochum built 15 Pfauter RS2 machines; and in autumn 1949 they moved to a former tank repair shop in Kornwestheim and built the RS1 and the small R16. The newly planned works in Ludwigsburg started up in 1951^[28] (the NDB gives 1948 for Ludwigsburg, and the Gleason-Pfauter history 1952^[1][8]). In 1961 the 20,000th machine was celebrated at Ludwigsburg; about 45% of the last 3,000 were built under license by Frieseke & Hoepfner and others^[28]. In the US, Fellows sold Pfauter hobbing machines under the name “Fellows-Pfauter,” and in 1961 brought out the P 630 for gears up to about 635 mm in diameter^[50]. Meanwhile, the main works in Chemnitz made a new start in 1950 as the people-owned enterprise VEB Zahnschneidemaschinenfabrik „Modul“ (Modul gear cutting machine works)^[32][1]. So from the same Pfauter line came two hobbing machine makers, “Pfauter” in the West and “Modul” in the East. Modul sold ZFWZ hobbing machines (ZFWZ 250 to 2000) through the East German export agency WMW, and at the 1982 Leipzig Spring Fair it also showed the ZFTKK 500/2 K hobbing machine for spiral bevel gears^[54].

Niles in East Berlin: the only gear grinding machine maker in the East

Niles in East Berlin became the people-owned enterprise VEB Deutsche Niles-Werke in February 1949, joined the Chemnitz machine tool association (VVB WMW) in 1950, and in 1952 changed its name to VEB Großdrehmaschinenbau “7. Oktober”^[9]. It was the only maker of gear grinding machines in East Germany; in 1958 it had orders for twice what it could build, and it exported to the Soviet Union, China, Poland, Czechoslovakia and North Korea^[9]. The ZSTZ 315 C of 1966 was shown at the Leipzig Spring Fair and sold to West Germany too, and the 1968 model already had program control. The machine tool research institute in Karl-Marx-Stadt (Chemnitz in the GDR era) and TU Dresden cooperated in its development^[9]. In 1970, two-flank grinding, which grinds the left and right flanks at the same time, cut grinding time by up to 40% and achieved accuracy of DIN 3962 grades 5–6^[9].

New faces in the West: Hurth's shaving, Liebherr, KAPP

In West Germany, mass production of cars created new demand for gear machines. In 1946, Hurth of München devised the first shaving machine for helical gears, or so it is said^[5]. Shaving finishes tooth flanks before hardening by meshing a gear-shaped cutter with fine serrations against the gear, with the axes slightly crossed, and shaving off a thin layer. It corrects the fine roughness and profile errors left by hobbing in far less time than grinding, so “hobbing → shaving → hardening” became the standard sequence for mass-producing transmission gears.

The crane maker Liebherr, finding transmission gears hard to obtain, began building its own hobbing machines in 1952 at its works in Kirchdorf an der Iller. In 1962 it moved gear cutting machine production to Kempten, and in 1969 this became Liebherr-Verzahntechnik GmbH^[36][37][3]. In 1967 it built the first gear shaping machine to use hydrostatic guideways, which float the slide on a film of oil^[3]. The aim was to reduce guideway wear on gear shapers, with their many reciprocating strokes, and to keep accuracy longer.

In Coburg in July 1953, the engineer Bernhard Kapp founded Maschinenfabrik KAPP & CO. It first built woodworking machinery and from 1958 moved into grinding machines for sharpening hobs and other tools^[9]. When CBN (cubic boron nitride, the hardest abrasive after diamond) wheels came onto the market in 1970, KAPP was quick to adopt them^[9].

Reishauer of Switzerland: continuous grinding with a threaded wheel

In neighboring Switzerland, in 1945 Reishauer brought out the ZA, a machine for continuous generating grinding, in which a threaded wheel shaped like a hob meshes and turns with the gear, grinding all the teeth without stopping^[31]. Faster than discontinuous generating grinding, this method later became the mainstream for finishing automotive transmission gears, and in Japan Mitsubishi Heavy Industries began producing gear grinding machines with Reishauer technology in 1966^[48].

Inside the machines of this era. On both hobbing machines and gear grinders, the rotation of tool (or wheel) and blank was matched mechanically by a master gear (master worm wheel) and a train of change gears. Accuracy was set by the accuracy of the master gear and the backlash in the gear train, and every time the number of teeth or the helix angle changed, the change gears had to be calculated and rearranged. That is why old used German machines often come with a change gear table.

NC, electronic gearboxes and CBN (1975–1994)

NC hobbing machines and the PE150

In 1975 Pfauter showed the first numerically controlled (NC) hobbing machine at the EMO machine tool show in Paris^[8][5]. The CNC hobbing machine PE150, first delivered in 1983, became the model Gleason calls “the best-selling hobbing machine of all time”^[8][5]. What NC meant was no more calculating and rearranging change gears: a setup change came down to entering numbers. The benefit was greatest for gear shops making many kinds of gears in small lots.

Electronic gearboxes: electronic synchronization began with the gear grinder

It was the former Niles in East Berlin that made the synchronization itself electronic. The ZSTZ 06 EG-CNC, unveiled in 1984, matched the rotation of wheel and gear with DC servo motors, electronic controllers and resolvers measuring the angle of rotation: an electronic gearbox (an electronic generating gear train). It was the first discontinuous generating grinder to have this together with CNC, and had been on trial runs at the research institute since 1983^[9]. With the master gear and change gears gone, a machine's accuracy was determined not by the gear train but by its motors, sensors and speed of control. This electronic gearbox idea would underpin the practical use of skiving 30 years later.

KAPP's CBN form wheels and profile grinding

In 1980 KAPP began developing CBN form wheels with a team of three, and while grinding internal splines it made its own electroplated CBN form wheels that need no reshaping (dressing). In 1982 its work on aircraft gears drew worldwide attention, and by 1984 it was making 500 wheels a month^[9]. In profile grinding, which grinds one space at a time with a form wheel, the wheel's shape becomes the tooth profile directly, so it suits CBN wheels, which hardly wear, and can grind shapes that are hard for a wheel to reach, such as internal gears and stepped shafts. In 1983 KAPP shifted its focus from hob grinders to gear grinders, bringing out the external and internal gear grinders VAG, VIG, VAS and VIS in turn. The VAS 531 of 1987 added a fifth NC axis and used a coarse and a fine CBN wheel in turn, nearly doubling productivity^[9].

Pfauter, the hobbing machine maker, also moved into grinding. In 1984 it signed an agreement with KAPP to take over grinding heads and CBN grinding technology and brought out the PFAUTERKAPP PE-G series for grinding gears up to 2,400 mm in diameter (the cooperation lasted until 1996), and in 1987 it built its own first profile grinding machine^[9][8]. Liebherr also brought out a gear grinder using CBN wheels in 1989^[3]. In the East, the former Niles built the large ZSTZ 2500 D in 1980, grinding gears of 250–2,500 mm diameter to DIN 3962 grade 4, and had switched to building machines from combinations of modular units^[9].

Reunification and restructuring

When the Berlin Wall fell in 1989, the eastern plants were suddenly in difficulty. The machine tool combine “7. Oktober” was broken up, and in May 1990 NILES Werkzeugmaschinen GmbH was formed under the Treuhand privatization agency, but exports to the East stopped and the workforce fell from 2,250 to about 1,600^[9]. Modul of Chemnitz was taken over by Hurth of München in 1993 and became Hurth Modul^[32][56].

Restructuring advanced in the West too. In 1991 Klingelnberg formed a joint venture with the bevel gear division of Oerlikon of Switzerland, and in 1993 it took over Oerlikon Geartec AG of Zürich^[22]. This brought the two lines that rivaled Gleason in bevel gear cutting (Klingelnberg's Palloid and Switzerland's Oerlikon method) into one company. Lorenz of Ettlingen had come under Switzerland's Maag in 1971^[2], but in the early 1990s Liebherr took it over, and Ettlingen became Liebherr's gear cutting tool plant^[3][55]. Maag itself delivered its last gear shaping machine in 1990 and stopped building gear machines^[20].

Dry cutting and finishing innovations

In 1994–95 Pfauter bought the gear cutting machine division of Mikron in Biel, Switzerland, and brought out the P100 for dry hobbing, which uses no cutting oil^[8]. Cutting fast with carbide hobs and carrying the heat away with the chips, it cuts the work of handling oil and washing parts. At EMO 2005, Liebherr's LC 120 and Fette's carbide hob demonstrated dry cutting from roughing to finishing with a single tool^[60]. In finishing, Hurth brought out a Spheric Honing machine in 1993, making it easier to apply profile modifications, such as slight crowning of the flanks, at the finishing stage^[5]. In 1994 Niles brought out the ZP profile grinder with a built-in wheel dressing unit, and KAPP the VAS 55 P, which grinds, measures on the machine and makes corrective grinding passes on a single machine^[9].

★Restructuring, dry cutting and skiving (1995 onward)

America's Gleason buys two German companies

In 1995 Gleason, the American bevel gear company, bought Carl Hurth Maschinen und Werkzeuge of München (shaving machines, gear grinders, honing machines)^[5][6]. Then in September 1996, just before the IMTS show in Chicago, it announced an agreement in principle to buy the Pfauter group. The group had about 1,050 employees and 1995 sales of $175 million, and negotiations had gone on in secret for several weeks^[57]. The acquisition was completed in 1997, and the Ludwigsburg company, as Gleason-Pfauter, became Gleason's development center for cylindrical gears, covering hobbing, shaping, skiving, profile grinding and more^[58][5]. In 2015 Gleason-Hurth's machine business was also consolidated in Ludwigsburg, and München became the tooling center^[8][5].

KAPP NILES and Klingelnberg

The former Niles in the East could not be revived even by a merger with Fritz Werner of the West, and filed for bankruptcy in February 1996. In 1997 KAPP took over NILES, forming the KAPP NILES group^[9]. In the same year, 1997, KAPP brought out the KX 1 for CBN continuous generating grinding with a threaded wheel, and in 2003 broadened it into the KX series, which can also use dressable wheels^[9]. The continuous generating grinding that Reishauer began in 1945 had become a mainstay of German grinding machine makers too.

In 1996 Klingelnberg bought Zeiss's gear measurement business in Ettlingen (formerly Höfler), and in 1997 it began dry cutting of bevel gears with the Oerlikon C 28. In 2008 it started up a large bevel gear plant in Hückeswagen-Winterhagen, in 2010 it moved its headquarters to Zürich, and in 2012 it bought Höfler Maschinenbau of Ettlingen (cylindrical gear grinders and measuring machines) as a core business. In 2018 it listed on the Swiss stock exchange^[22].

What became of Modul in Chemnitz

The Chemnitz hobbing machine plant has carried on through many changes of owner. In 2000 Samputensili of Italy bought Hurth Modul^[56]; in 2010 the American machine tool group MAG bought it, making it MAG Modul Verzahntechnik; in 2013 it came under the FFG group; and in 2024 it became an independent company again (MODUL MT Verzahntechnik). It still builds hobbing machines for gears up to 2,300 mm in diameter and module 28^[61][32][33]. The grouping of gear machine makers has gone further: the lathe maker EMAG took over the Furtwangen hobbing machine maker Koepfer in 2005 and Samputensili Machine Tools of Italy in 2021 (the chapter on Italian gear machines)^[59].

Skiving: a patent asleep for 100 years wakes up

About 100 years after the 1910 patent, in the early 2010s, skiving (power skiving) became a mass-production method. Gleason-Pfauter rounded out its range of skiving machines in 2012^[8], and PITTLER T&S, which carries on the Pittler name, Profilator of Wuppertal and Liebherr also brought out machines^[17][62][3]. In Japan, too, a Pfauter gear skiving machine was described in a trade journal in 1969, and there was a technical tie-up in 1971^[51][52], but skiving spread only in the 2010s.

Why did it take 100 years? In skiving, the cutting speed is the sliding speed that results from the crossed axes of tool and blank. To get enough cutting speed, tool and blank must turn at high speed and stay precisely synchronized, without slipping even one tooth. With a mechanical gear train, backlash and vibration in the train ruined accuracy, and tools wore quickly. PITTLER T&S explains that only recent advances in electronic synchronization (electronic gearboxes) finally made it economical^[17], and a paper of the Japan Society of Mechanical Engineers concludes that its advantages became clear with progress in tool materials combined with CNC^[16].

The difference in speed is clear in numbers. Profilator explains that a 60-tooth tool at 2,000 rpm means 120,000 cutting edges cut the workpiece per minute, whereas gear shaping at 1,800 strokes per minute gives only 3,600^[62]. Its strengths are that it can cut internal gears several times faster than a gear shaper and can be used on stepped gears without a relief groove^[62]. Tool life, chip evacuation and the difficulty of tool design remain challenges today; they are covered in detail in the article "New technologies that solve two weaknesses of gear skiving".

Today's Players

Current makers' machines and tools are summarized in Makers of gear cutting tools and gear machines.

Research and standards: FZG, WZL, DIN, ISO

Niemann and the FZG: deciding gear strength on test rigs

Behind the strength of German gear machines lies research that determines “how far” gears can be used. Niemann, who had begun gear research in Braunschweig, founded in München in 1951 the FZG (Forschungsstelle für Zahnräder und Getriebebau, Gear Research Centre)^[26] (the NDB dates the founding of the FZG to 1948, which can also be read as the name of his institute from the Braunschweig days^[25]). Niemann studied flank strength and lubrication using the back-to-back test rig (Verspannungsprüfstand) built by Heinz Glaubitz, which connects two gearboxes and runs them under a locked-in torsional load, and from 1950 also a pulsator that applies repeated loads^[25]. The test Niemann devised in 1952–53 to find, step by step, the load at which a lubricant lets tooth flanks scuff became DIN 51354 in 1959 and is still called the “FZG test”^[25].

Niemann's textbook Maschinenelemente (Machine Elements) first appeared in 1950 and was translated into many languages, including Japanese. From 1950 he held a conference on gears and transmissions with the VDI every two years, and in 1965 he became an honorary member of the Japan Society of Mechanical Engineers^[25]. The FZG was later led by Hans Winter (from 1968), Bernd-Robert Höhn (from 1989) and Karsten Stahl (from 2011), and is deeply involved in standards work^[26].

The WZL in Aachen: research on the “making” side

If the FZG does research for those who use gears, the WZL in Aachen does it for those who make them. In 1956 Herwart Opitz of the WZL formed a gear research circle, the “Getriebekreis,” with company representatives, as a forum for researching gear strength, noise and cutting methods jointly with member companies at the pre-competitive stage. Since 1959 it has held an annual research conference (Getriebetagung)^[44]. This WZL Getriebekreis continues today^[45], and the WZL once kept many gear test rigs in an old military bunker^[65]. The story of the WZL and Schlesinger's science of production engineering is covered in Chapter 2, “Production Engineering as a Science”.

From DIN to ISO

For a long time the yardstick for accuracy grades was Germany's DIN 3962 grades. The underlying DIN 3960 and 3961 appeared around 1953–54 and divide accuracy into 12 grades^[39][40]. The Niles timeline, too, describes the 1970 two-flank grinding as “DIN 3962 grades 5–6” and the 1980 large grinder as “grade 4”^[9]. The international standard ISO 1328, in its 3rd edition of 1975, set out definitions and tolerances for individual errors together with advice on measurement; ISO 1328-1 of 1995 narrowed it to the definitions and tolerances of flank deviations (pitch, profile, helix); and the 2nd edition of 2013 added methods for evaluating profile and helix and brought runout evaluation back into Part 1^[53]. Japan's JIS B 1702-1 was aligned with this 2013 edition in 2016 (for how to read accuracy grades, see "Gear study"). When converting “Qualität 6 nach DIN 3962” on an old German drawing to today's ISO or JIS grades, remember that each standard has different error items and tolerance formulas: do not assume that the same number means the same accuracy, and check against the tables of the original standard.

Links with Japan

Each milestone in the history of Japanese gear cutting is linked to machines from the German-speaking world (for details, see the Japanese Archive, Chapter 4 timeline).

• The first hobbing machines: Around 1906, Pfauter hobbing machines were imported by Ishikawajima and the Kure Naval Arsenal; they are considered the first hobbing machines in Japan^[12][13]. Around 1918 the tooth form, gear cutting machines and gear grinders of Maag of Switzerland were introduced and won a good reputation^[12], and in 1920 a 40-inch hobbing machine modeled on the Pfauter was completed at Kashifuji Iron Works (today's Kashifuji)^[12][24]. The workings of Maag gears were also explained in research by Naruse Masao and others at Tohoku University (People).
• Postwar technical tie-ups: In 1961 Mitsubishi Heavy Industries formed a technical tie-up with Lorenz of West Germany for gear cutting machines and began building the “Mitsubishi Lorenz” vertical hobbing machine (first unit in 1962). It ended the tie-up in 1971, switched to its own technology and brought out the GH series in 1972^[48][49]. In 1966 it began producing gear grinders with technology from Reishauer of Switzerland^[48]. In 1971 Nachi-Fujikoshi formed a tie-up with “a West German specialist hobbing machine maker” for internal gear skiving machines and production hobbing machines (we could not confirm the partner's name from the sources)^[52][13].
• Skiving: In 1969 the Japanese trade journal Machinery (Mashinari) described Pfauter's P630WS gear skiving machine^[51]. Japanese makers' skiving machines and cutters were all on the market by 2014: as in Germany, a comeback that had waited on electronic gearboxes and advances in tooling^[24][63].
• Research and companies: Niemann became an honorary member of the Japan Society of Mechanical Engineers in 1965, and Maschinenelemente was translated into Japanese as well^[25]. Klingelnberg set up a subsidiary in Japan around 1954 (its 70th anniversary was in 2024)^[22], and in 1988 KAPP set up KAPP Tools in Japan to license CBN tool replating technology to Japanese customers^[9].

FAQ

Did Pfauter invent the hobbing machine?

The idea of generating teeth with a hob, and early hobbing machines, existed in 19th-century Britain and America, and in Germany with Juengst (1893) and Reinecker (1894). Pfauter's achievement was to bring together the form of today's hobbing machine: tilting the hob axis to any angle and adding to or subtracting from the blank's rotation with a differential, so that a single machine could cut even helical gears. This can be confirmed in German Patent DRP 112082 (filed September 1, 1897) and US Patent 640,728 (granted 1900).

Why did skiving take 100 years to become practical?

Skiving uses the sliding created by the crossed axes of tool and blank as the cutting speed, so both must be kept turning at high speed in precise synchronization. With a mechanical gear train, backlash and vibration ruined accuracy and tool wear was severe. Only in the 2010s, when the electronic gearboxes first used on gear grinders in the 1980s (matching rotation with servo motors and sensors) came together with advances in tool materials and coatings, did it finally become usable in mass production.

How do Klingelnberg's Palloid and Gleason's methods of cutting bevel gears differ?

The spiral bevel gear machine Gleason brought out in 1913 cuts one tooth space with a cutter head, then indexes the blank to the next space. Klingelnberg's Palloid (from 1922) keeps the blank turning while the conical hob rotates, cutting without stopping to index. In the 1990s Klingelnberg took over the bevel gear division of Oerlikon of Switzerland, bringing together one side of the two lines. The Gleason side is covered in the chapter on American gear machines.

What happened to East Germany's gear machine makers?

VEB Modul in Chemnitz (the former Pfauter main works) passed after reunification through the hands of Hurth, Samputensili of Italy, MAG of the US and the FFG group, and became independent as MODUL MT in 2024. The former Niles in East Berlin, the East's only gear grinder maker, went bankrupt in 1996 and in 1997 was taken over by KAPP of Coburg to become KAPP NILES. Both still build gear machines today.