USA 07The Lineage of American Milling Machines and Machining Centers

Armory milling machines and the Lincoln miller (1808–1860)

In the early 19th century, the flat faces and curved edges of gun parts were finished by craftsmen with files. Factories supplying guns to the government were required to make parts that would fit any gun (interchangeability), and they kept working to replace filing with machines. Out of this came the machine that feeds work into a rotating cutter: the milling machine.

Who built the first milling machine?

For a long time the “first milling machine” was said to be the machine at Eli Whitney's armory in Whitneyville, near New Haven. Roe found it in 1912 and dated it 1818, based on an encyclopedia sentence stating that the first crude milling machine was built in a Connecticut gun factory in 1818^[1]. Woodbury, however, points out that the basis for that sentence is unknown, and that similar machines existed around the same time at the gun works of Simeon North and Robert Johnson in Middletown. The first firm evidence of milling at Whitney's plant is a letter to the Secretary of War in March 1823, by which time milling was also in use at the Springfield and Harpers Ferry armories. He also writes that North may already have been using it in 1808^[1]. Later research by Woodbury and Battison dated the Whitney machine to around 1827, after Whitney's death, and the American Precision Museum also explains that it had long been mistaken for the first milling machine^[4]. The historian Merritt Roe Smith regards a light machine that North built around 1816 as the oldest known milling machine in the United States^[2].

Who came first cannot be settled, but what the machine was like is clear. The Whitney machine was a small one, about 45 cm high. For the automatic table feed it used a feed screw and nut, not a rack and pinion, and it had a box-shaped frame and gibs (strips on the slideways that take up wear). It had no means of changing the spindle height; the height seems to have been set by putting paper or thin metal shims under the work. Woodbury sees this as the beginning of the “knee type”^[1]. The Middletown machine had a small cylindrical cutter whose teeth were cut with a file; craftsmen at first dismissed it as a mere “substitute for filing,” but it is said they later came to use it for roughing flat faces^[1]. In today's terms, the early milling cutter was a rotating file.

Designs that grew up in the armories

In the 1830s the Springfield Armory used a fixed-spindle machine to mill the flat faces of monkey wrenches, and in 1835 it had a machine built whose cutter height could be changed with a lever^[1]. The machine at Gay & Silver's works in North Chelmsford was the first to show a means of changing the spindle height and an overarm supporting the outer end of the cutter arbor. Frederick W. Howe, who trained there, would become the central figure in milling machine design^[1].

In 1848 a plain milling machine designed by Howe was built at Robbins & Lawrence in Windsor, Vermont. It gained power with a wide belt pulley and back gearing, supported the arbor on the outside, and was made heavy overall, coming closer to both accuracy and heavy cuts. But because its feed was rack and pinion, it chattered when entering heavy cuts^[1][5]. The same year, at Colt's armory, E. K. Root built a machine with an automatic feed stop and a clutch, and in 1854 he replaced the arbor support with a cylindrical overarm like today's, making it an open-sided machine^[1]. In 1852 Robertson's milling machine became the first milling machine patented in the US. Its spindle, bearings and gears were mounted together on a heavy vertical slide that moved up and down, and Woodbury judges it technically more advanced than the Lincoln miller^[6][1].

Lincoln miller: the first “production milling machine”

In 1855 George S. Lincoln & Co. of Hartford built milling machines designed by F. A. Pratt for Colt's new armory. Modeled on the Robbins & Lawrence machine brought to Hartford a year or two earlier, it was made sturdy and compact overall. Replacing the chatter-prone rack-and-pinion feed with a feed screw and nut was Pratt's big improvement^[5][1]. Named after the plant that built it, the “Lincoln miller” was made by the thousands and sold around the world. Most of them were built by Pratt & Whitney, which Pratt and Amos Whitney started in 1860^[1][5].

The Lincoln miller was a “bed type”: the spindle was fixed to the frame and the table only fed back and forth, which suited milling hundreds of the same part. Woodbury sums up that by 1860 the milling machine had become indispensable in American metalworking and helped turn out guns in quantity for the Civil War^[1]. But even Pratt had not yet found a good way to adjust the cutter height.

Why a feed screw? A rack and pinion can move a long distance quickly, but play in the mesh (backlash) and deflection make the table jump at the start of a cut and invite chatter. A feed screw and nut has a large reduction ratio, and the cutter has a hard time pushing the table back, so it can feed at a steady rate even in heavy cuts. The Lincoln miller spread because this “steady feed” made production work uniform. Later, as backlash-eliminating devices and precise gear cutting advanced, rack and pinion came back into use^[1].

The universal milling machine and the knee type (1861–1899)

A universal milling machine born from drill flutes

At the start of the Civil War, Providence Tool Co. was making rifles for the government. Howe, by then its superintendent, saw craftsmen filing twist drills with helical flutes out of round bar and asked Joseph R. Brown of Brown & Sharpe about a cheaper way to make them. Brown himself had just started using such drills on sewing machine parts (Wilcox & Gibbs)^[5]. The machine Brown drew in 1861 was built to handle any helical-groove, gear or indexing work, not just drill flutes^[1]. The first machine was sold to Providence Tool Co. on March 14, 1862; ten were sold that year, and the first export went to France. It was first described in print in Scientific American in December of the same year^[5][1]. The patent was granted in February 1865^[8].

Three things were new. The table sat on a saddle that swiveled horizontally and moved in and out on a knee that rose and fell; an index head (spiral head) geared to the table feed screw cut helical grooves; and the index head could index while tilted, too^[1]. Swiveling the table lets you cut at the helix angle of the groove without tilting the cutter. The index head grew out of Brown's experience building bevel gear cutters, and including functions the drill work did not need is what made the machine “universal”^[1]. Around the same time, Howe had designed a machine called “universal” in 1852, and which came first later became a dispute, but both Roe and Woodbury credit Brown with inventing the universal milling machine in today's sense^[5][1].

The knee-type answer

To the problem, ongoing since the armory era, of how to match the heights of cutter and work, Brown's answer was to raise and lower the knee on the front of the column. With the spindle fixed in the frame, the table, saddle and knee are raised and lowered together by a screw, so belt tension does not change and the height can be set precisely. Woodbury calls this the “final solution” to the cutter-height problem^[1]. At about the same time, Garvin's plain milling machine combined the knee type with an overarm, becoming the prototype of today's knee-type milling machine. At the 1876 Centennial Exhibition, Brown & Sharpe showed a universal milling machine nearly twice the size, with back gears and an overarm added, and milling machines spread from light toolroom work to heavy work such as locomotive parts^[1].

On accuracy, Brown & Sharpe's 1867 catalog lists a machine whose longitudinal and vertical feed screws had graduated dials reading to 1/1,000 in. (about 0.025 mm). Woodbury considers this the first use of such graduations on a machine tool^[1]. Positions that craftsmen had set with rules and scribed lines could now be set by the dial on the handle.

Form cutters that keep their shape when sharpened

Brown also set a milestone on the cutter side. Gear cutters around 1850 had teeth cut with chisel and hammer; every resharpening meant annealing, hammering the teeth back, filing to a template, filing in the clearance and hardening again^[1]. The form cutter Brown patented in November 1864 had constant clearance behind the teeth (what we now call a backed-off tooth profile), so that grinding only the face gave the same tooth profile however many times it was sharpened^[7][1][5]. Over the next 40 years, patents followed one after another for the basic forms of today's milling cutters: uneven-pitch teeth, inserted-blade face mills, helical teeth and more^[1].

The beginnings of the vertical milling machine

With its spindle standing upright, the vertical milling machine is already drawn in well-developed form in W. B. Bement's 1862 patent. In 1870 James Watson patented a vertical milling machine for keyways, and in 1883 L. Cosgrove combined a knee-type table with a spindle head that could tilt from vertical to horizontal. In 1888 Brown & Sharpe brought out a vertical milling attachment for plain milling machines^[1]. The vertical type uses end mills, so the spindle must run fast, and improvements in bearings and lubrication continued. It could mill the top and both sides of a heavy casting without resetting and also suited tracing and die sinking, which is why the vertical type later became mainstream^[1].

Cincinnati, Rockford, Milwaukee

In the late 19th century milling machine builders spread into the Midwest. In Cincinnati, Frederick Holz, who had begun making screws and taps in a kitchen around 1880, built himself a wooden-frame milling machine to mill tap flutes; customers who saw it placed orders, and that started the milling machine business. In 1889 the company became Cincinnati Milling Machine Co., with Frederick A. Geier as president^[5]. In 1881–82 it brought out machines with “centralized control,” with the feed handles arranged diagonally so they could be worked from one place, and with left-hand spindle rotation so that drill press and lathe tools could be used as they were^[1]. In 1896 Holz devised an adjustable brace clamping the overarm and knee together through slots, to keep the arbor from deflecting in heavy cuts^[1].

Around 1893 Ingersoll Milling Machine Co. moved from Cleveland to Rockford, Illinois, and took the lead with heavy planer-type millers that mounted several spindle heads on a portal frame like a planer's^[5]. In Milwaukee, Wisconsin, Theodore Trecker, superintendent at Kempsmith, and the design engineer Edward J. Kearney started Kearney & Trecker in 1898^[9], and in 1916 Roe listed it, along with Kempsmith, as a “well-known milling machine builder”^[10][5].

Gearboxes, electric motors and production milling machines (1900–1926)

After Brown set the basic form, the most important developments in the milling machine were the feed mechanism and its control, and how power was connected to the spindle, Woodbury writes^[1]. Around 1900, milling machines took power by belt from a long overhead line shaft, changed speed by shifting the belt on cone pulleys, and also took the feed from the spindle by belt. Changing spindle speed also changed the feed, and a small end mill and a large face mill got the same power, which was inconvenient.

Constant-speed drive and all-gear design

At the 1900 Paris Exposition, Cincinnati's new milling machine won a gold medal. Driving all feeds positively through gears, it was the first milling machine to do so^[1]. In December the same year, John Parker of Brown & Sharpe wrote up in a memo the idea of a “constant-speed drive”: run a single belt at constant speed and change both spindle speed and feed through gears. Run fast for small cutters and gear down for power with large ones, and take the feed from a separate constant-speed shaft rather than from the spindle; the No. 2 universal milling machine of 1901 became the first machine with an all-gear constant-speed drive^[1].

From overhead belts to electric motors

Around the same time, a movement began to give each machine its own motor. In 1901 Brown & Sharpe tried coupling a General Electric four-speed DC motor to the spindle, but to deliver power at low speeds the motor had to be large and expensive, and at coarse feeds it used too much electricity. Coupling a variable-speed motor directly to the spindle was not the answer. The answer was to drive a constant-speed gearbox with a motor running at constant speed. In 1903 Cincinnati put on sale a machine combining a constant-speed motor, a friction clutch and an all-gear spindle drive, and in 1919 Brown & Sharpe put the motor inside the frame of a knee-type machine. Woodbury says this is where the spindle and its drive took their present form^[1].

High Power and the science of cutting

In 1907–08 Cincinnati brought out its “High Power” milling machine. Built with the feed mechanism grouped into units mounted on the frame (Holz's 1900 patent), it had separate spindle and feed drives, and the feed could be selected either per minute or per spindle revolution. Set the feed by the feed per tooth, and the speed by how much heat the cutter can stand: this, today's approach to cutting conditions, was built into the machine here^[1].

Cutters changed too. High-speed steel from Taylor and others raised cutting speeds 2–2.5 times, forcing machines to be redesigned^[5]. Cincinnati's A. L. De Leeuw studied the forces on milling cutter teeth by experiment and showed that the cutters of the day broke before the machine's power was used up. A face mill with wider tooth spacing and stronger teeth increased the metal removed per horsepower by 50%^[1][5]. By 1918 nearly every maker had also adopted pumped cutting fluid, with the frame serving as the tank^[1].

Production milling machines and the automobile

Auto mass production demanded that milling machines cut “fast, the same part every time, with fewer hands.” The large Ingersoll milling machine installed at Ford's Highland Park plant in 1912 served just two operations on the Model T cylinder block^[13]. In 1913 Cincinnati built for Ford a rotary-table special machine to mill cylinder heads, with even the work clamping automated by cams^[1].

Also in 1913, Cincinnati's automatic milling machine designed by De Leeuw set the pattern for the bed-type production milling machine (manufacturing milling machine). By 1916 plain and duplex types that automatically repeated the table cycle (approach at rapid traverse, cut at feed, return at rapid traverse and stop) were available, replacing Lincoln-type machines. Woodbury points out that the ancestor of the Cincinnati machine was the Lincoln miller. The knee type was too complex to automate and became a machine for the toolroom and small lots, while the simple bed type carried production automation^[1]. The vertical type was also used as early as 1903 for “jig boring,” locating holes in jigs on a Brown & Sharpe machine with graduations and verniers, and in 1910 Le Blond brought out a vertical milling machine for jig boring^[1].

Hydraulics, tracing and turret mills (1927–1951)

Die sinkers and tracing

After World War I, demand for forging, casting and press dies grew, and a way faster and cheaper than cutting by skilled die sinkers was sought^[1]. The idea of tracing a master to cut the same shape goes back to Blanchard's gunstock lathe of 1818, but cutting iron required pressing hard on the master, which soon wore out^[1]. At an exhibition in Detroit in October 1922, Keller of Brooklyn demonstrated an automatic die sinker that traced plaster, cement or wood masters with light force to cut crankshaft forging dies^[15]. A tracer that transmitted motion electrically with only a light touch on the master, filed by J. C. Shaw in 1920, later became the principle of the Keller die sinker^[1]. Pratt & Whitney bought Keller's company in October 1931 and moved it to Hartford, and the Keller die sinker became known as the “Pratt & Whitney Keller”^[19].

Hydromatic: the hydraulic production milling machine

In 1927 Cincinnati brought out the first production milling machine with table feed driven and controlled hydraulically: the bed-type Hydromatic. The feed was stepless; cams changed the feed rate so that it cut with constant force even as the width or depth of cut changed, and cams raised and lowered the spindle head to step over shoulders or follow contours. A dwell device that stopped and paused at a set position let it finish exactly to depth without leaving tool marks^[1][16]. Also in 1927, G. V. Anderson of Philadelphia filed a patent for a tracer milling machine worked entirely by hydraulics (assigned to Cincinnati), and Cincinnati applied it to an automatic die sinker in 1932, a vertical milling machine with automatic depth control in 1935, and, in 1936, the hydraulic vertical milling machine Hydro-Tel, one after another^[1].

Removing backlash for climb milling

As production advanced with hydraulic and mechanical automatic feeds, work such as turbine blades, where tool marks would not polish out, became a problem. Conventional milling, with the cutter turning against the direction of feed, left marks; climb milling, with the cutter turning the same way as the feed, left none, but with play in the feed screw the table could be pulled into the cutter, which was dangerous. Around 1935, backlash eliminators (Brown & Sharpe used De Vlieg's design, and Cincinnati refined Holz's idea) made climb milling usable, and efficiency also rose by cutting alternately at both ends of the table^[1].

Carbide face mills

High-speed steel was still the main cutter material. Cincinnati's 1938 handbook Milling Machine Practice lists four cutter materials (carbon steel, high-speed steel, Stellite and carbide) and says most heavy-duty cutters were high-speed steel, which could run 2–2.5 times faster than carbon steel. It then notes that for face milling cast iron, face mills with inserted carbide blades were being run at 2–3 times the speed of high-speed steel, gave a better finish, and were replacing other cutters (1937)^[22].

Bridgeport turret mill

At the opposite end from the big plants' production milling machines, the machine that changed small job shops was the Bridgeport. Rudolph Bannow, who bought a pattern shop in Bridgeport, Connecticut, in 1927, teamed up with Magnus Wahlstrom in 1929, and in 1932 they put on sale the “Model C,” a portable high-speed milling head with a 1/4 hp motor. In 1936, in a truck on the way to deliver patterns, Bannow is said to have sketched a machine built around this milling head on a paper bag^[20][23][21].

The machine, the first of which shipped in 1938, mounted the milling head on a ram that slid in and out and a turret that swiveled horizontally, let the head itself tilt, and combined all this with a knee-type table. Without moving the work, it could drill, slot and cut angles by changing the position and angle of the cutter, and it could also drill with the quill (a hollow sleeve) that moved the spindle up and down^[20][24]. The company became Bridgeport Machines, Inc. in 1939, and Bannow said that raising the price by 12% to $1,575 in 1951 was the only price increase in 20 years^[24]. More than 250,000 Bridgeports were built (some sources say over 330,000), becoming the foundation of die and jig making in thousands of job shops^[20][21].

①From NC milling machines to machining centers (1952–1977)

The Hydro-Tel becomes NC

In 1952, under an Air Force contract, MIT's Servomechanisms Laboratory removed the drives and controls from a large Cincinnati Hydro-Tel vertical milling machine and built an NC milling machine that moved three axes simultaneously from punched-tape commands. In 1959 Woodbury called this the most important recent advance in milling machines, writing that it was significant that NC was first applied to the milling machine, the most versatile of machine tools^[1]. Tracer milling machines needed handmade masters, but NC could cut 3D shapes directly from the numbers on the drawing. The story of how NC was born (Parsons's proposal, the APT language and more) is told in Chapter 4.

The Air Force's 100 machines and five axes

It was the Air Force that created a market for NC milling machines. In 1955 it began awarding contracts for 100 NC milling machines (worth $35 million in total)^[28]. The core of the program was skin mills for machining aircraft skins and profilers for wing members, and Kearney & Trecker won about a quarter of the contracts^[29]. In October 1957 Giddings & Lewis's magnetic-tape-controlled “Variax” became the first five-axis, single-spindle profile mill to pass Air Force acceptance tests^[30]. Around 1960 Sundstrand of Rockford brought out the five-axis “Omnimill”^[34]. Five-axis machining, cutting while changing the tool's orientation, thus began with aircraft parts (for 5-axis machining today, see our 5-axis machining guide).

Milwaukee-Matic: the machine that changes its own tools

In the mid-1950s, seeing demand for standard machines falling, Kearney & Trecker began thinking about a machine that would finish small lots of parts on a single machine^[29]. What chief engineer Wallace E. Brainard, who had come from Hughes, and his team built was a tool changer (ATC) that picks the next tool from storage and swaps it with the tool in the spindle using a two-armed change arm. The patent was filed on June 27, 1958, and granted on September 4, 1962^[31][32][33].

Fitted with this ATC, the Milwaukee-Matic was advertised in a January 1959 trade journal as “a flexible automated machining center.” It did milling, drilling, reaming, tapping and boring on one machine, and General Electric punched tape controlled everything down to tool selection, table indexing, spindle position, speed and feed. On one part, 49 operations that had taken several machines and fixtures were done in one fixture and one setup^[12][29]. This ad already uses the term “machining center.”

According to Control Engineering of March 1960, Kearney & Trecker took orders for 55 Milwaukee-Matics in 1959 and delivered 30, building more NC machine tools that year than anyone else. The keenest buyers were not aircraft companies but missile parts makers with frequent design changes. Users reported one machine doing the work of four or five, and the sales manager said tooling costs fell to between one-third and one-tenth. The model on sale was the Model II (no Model I was built), and a Model III twice the size was in preparation^[29]. The ATC patent was later fought over in a long lawsuit with Giddings & Lewis^[32]. Cincinnati also brought out the CIM-X, a machining center run by paper tape, by 1965, and fitted it with a tool changer in 1968^[35][36].

What became of Bridgeport and Cincinnati

In 1968 Bridgeport Machines was bought by the conglomerate Textron. By 1970 an NC version of the Series I and the Series II had appeared, and in the 1970s Adcock & Shipley of Britain became Bridgeport's European base^[21]. In 1971 Hurco of Indianapolis began developing, for Bridgeport-type knee mills, a control that operators could program themselves on the shop floor, and at IMTS 1974 it showed that control along with a prototype of its first CNC machining center^[40]. In 1970 Cincinnati Milling Machine Co. changed its name to Cincinnati Milacron, as it was no longer just a milling machine company^[39].

★The spread of the vertical MC and the reshaping of old makers (1978–)

CNC and the vertical MC

In the late 1970s CNC, with a computer built into the NC unit, spread, and programs could be edited at the machine. In 1978 Bridgeport brought out a CNC milling machine said to cut programming time by up to 90%^[21]. Cincinnati Milacron was one of the few makers that built both the machines and the CNC (Acramatic) in-house, and a government guide to NC machines shows its vertical milling machine fitted with an Acramatic^[41].

Around the same time, machines from Asian makers entered the US market and gained a foothold with standard machines, CNC lathes and simple MCs^[21]. New US makers that fought back on price grew up as vertical MC specialists. Started in their father's garage shop, the de Caussin family's Fadal brought out its first vertical MC in 1980, kept prices down by building its own controls, and had sold 10,000 by 1995^[45]. Starting out with indexers, Haas Automation showed its first vertical MC, the VF-1, as a prototype at IMTS 88 in 1988. Its list price of $49,900 put a US-built MC under $50,000^[48][49]. The vertical MC went on to replace the job-shop work once done on knee mills and drill presses with a single machine run by a program.

The copied Bridgeport

The Bridgeport's form spread so widely that it came to be copied. Textron sued, claiming that vertical mills coming in from Taiwan imitated the look of the Series I, but the International Trade Commission (ITC) found no violation, and in January 1985 the Court of Appeals for the Federal Circuit upheld that finding. The reason was that the shape of the machine as a whole is a functional shape and so cannot be protected as a trademark. Eighteen Taiwanese companies and others, including YCM (Yeong Chin Machinery), took part in the case^[47][21]. “Bridgeport type” even became a name for a class of machine, and Hurco's first control, too, was made for a “Bridgeport-type knee mill”^[40].

Reshaping of the old makers

From the 1980s to the 2000s, milling machine makers dating back to the 19th century changed shape one after another. Kearney & Trecker merged with Cross Company in 1979 to become Cross & Trecker, which Giddings & Lewis bought in 1991^[42][44]. Fadal was also sold to Giddings & Lewis in 1995^[45][51]. Cincinnati Milacron sold its machine tool business to UNOVA in 1998 and became Milacron, a plastics machinery company^[52] (Cincinnati Machine was sold by UNOVA to MAG Industrial Automation Systems in 2005^[55]), and Brown & Sharpe sold its metrology business to Hexagon in 2001^[53]. The Bridgeport business was taken over in 2004 by the lathe maker Hardinge^[54]. The decline of the US machine tool industry as a whole and the voluntary restraint on imports (VRA) are covered in Chapter 5, “The wave of imports and revival”.

What it means on the shop floor. When looking at an old milling machine, ask: Is the feed by screw or by rack, and is there backlash elimination (can it climb mill)? Is the spindle driven by cone pulleys or a gearbox, and is the motor inside the frame? Is it a knee type, a bed type, or a Bridgeport-type ram and turret? Are tools changed by hand or by ATC? The answers tell you the machine's generation and what it does well. Climb milling is routine on today's MCs, but the warning that it is dangerous on old general-purpose machines without backlash eliminators comes from this history. The basics of how we cut today are summarized in Machining basics.

Links with Japan

Japanese milling machines grew up first on the model of the American Cincinnati design. In 1925 Tokyo Gas & Electric Industry began building milling machines modeled on Cincinnati's, and also studied the improvements in imported Cincinnati and Kearney & Trecker machines. In 1941 Osaka Kiko (OKK) developed the knee-type MH-3V based on Cincinnati's No. 3 milling machine, making it the prototype of its knee-type line (Japanese Archive, Chapter 2). The lineage of the “knee type,” “centralized control” and “High Power” seen in this chapter thus went straight into Japanese factories.

After the war, in bed-type production milling machines, Niigata Engineering signed a technical tie-up in 1954 with Sundstrand of Rockford. When Niigata Engineering built the MC 50DIU in 1968, with a spindle head that turned between vertical and horizontal, it developed the machine in-house after also studying information on Sundstrand's much-discussed MC, the “Omnimill” (Chapter 2, Postwar, Birth of the MC). Nihon no Gijutsu 100-nen (100 Years of Japanese Technology), which describes the beginnings of the MC in Japan, names Kearney & Trecker's Milwaukee-Matic as the world's first MC (giving the year as 1957), and in Japan a Hitachi group built an NC universal machine tool with a two-armed ATC in 1960 (Chapter 2). Makino's NC milling machine of 1958 also came six years after MIT's NC milling machine (Chapter 2, NC).

The flow reversed in the 1970s. Matsuura Machinery began exporting vertical MCs to the US in 1975, and Osaka Kiko also exported many of its low-priced 1977 vertical MCs to the US and Europe. In 1982 US machine tool makers petitioned the US government to exclude Japanese-made MCs and other machines from the investment tax credit, and in 1987 voluntary restraint on exports of NC lathes, MCs and others to the US (VRA) began (Chapter 2, American Chapter 5). The Haas VF-1 appeared as “a US-made MC under $50,000” right in the period of these restraints.

In Britain, Cincinnati began building machines in Western Europe in 1934 (The Lineage of British Milling Machines and MCs)^[39], and Bridgeport made Adcock & Shipley of Britain its European base^[21]. Brown & Sharpe's 1937 Omniversal was widely copied in Britain, France, Germany and Italy^[1] (Germany, Italy chapters on milling machines).

FAQ

Did Eli Whitney build the first milling machine?

It is not clear. The machine from Whitney's factory is considered the oldest surviving milling machine. Roe dated it to 1818, but later research suggests it was made around 1827, after Whitney's death. Similar machines existed in the 1810s–20s at the shops of Simeon North and Robert Johnson in Middletown and at the Springfield and Harpers Ferry armories. What is certain is that the milling machine grew up at about the same time in several gun shops, to replace hand filing of gun parts.

What is the difference between a universal milling machine and a knee-type milling machine?

“Knee type” refers to the layout in which the table height is changed by raising and lowering the knee on the front of the column; most general-purpose milling machines today are of this type. A universal milling machine is a knee-type machine with a table that swivels horizontally and a dividing head geared to the feed screw, so it can cut helical grooves and gears. Both forms were settled by Brown & Sharpe's machines of 1861–62.

What was the first machining center?

The Milwaukee-Matic of Kearney & Trecker (Milwaukee). It had an ATC whose two-armed exchange arm changed tools automatically, and punched tape controlled everything from tool selection to table indexing. The ATC patent was filed in June 1958, and the machine was advertised as a “machining center” in a trade journal in January 1959 (some sources give 1957).

Why did the Bridgeport milling machine spread all over the world?

The head, mounted on a ram and turret, can be swung forward and back and side to side, and tilted, so you can cut at many positions and angles without moving the workpiece, and drill holes with the quill. One machine could handle most die, jig and prototype work at an affordable price, so more than 250,000 were built and it became the standard machine of small job shops. Machines of the same form were built in Taiwan and elsewhere, and in the 1980s there was even a lawsuit over its appearance.