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In metalworking and woodworking, an automatic lathe is a
lathe A lathe () is a machine tool that rotates a workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, and turning, with tools that are applied to the workpiece ...
with an automatically controlled cutting process. Automatic lathes were first developed in the 1870s and were mechanically controlled. From the advent of NC and CNC in the 1950s, the term automatic lathe has generally been used for only mechanically controlled lathes, although some manufacturers (e.g., DMG Mori and Tsugami) market Swiss-type CNC lathes as 'automatic'. CNC has not yet entirely displaced mechanically automated lathes, as although no longer in production, many mechanically automated lathes remain in service.


General nomenclature

The term "automatic lathe" is still often used in manufacturing in its earlier sense, referring to automated lathes of non- CNC types. The first automatic lathes were mechanically automated and controlled by cams or tracers and
pantograph A pantograph (, from their original use for copying writing) is a mechanical linkage connected in a manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen. If a line dr ...
s. Thus, before electronic
automation Automation describes a wide range of technologies that reduce human intervention in processes, namely by predetermining decision criteria, subprocess relationships, and related actions, as well as embodying those predeterminations in machines ...
via
numerical control Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a computer. A CNC machine processes ...
, the "automatic" in the term "automatic machine tool" always referred implicitly to ''mechanical'' automation. The earliest mechanically automated lathes were geometric lathes, including rose engine lathes. In industrial contexts during the Machine Age, the term "automatic lathe" referred to mechanical screw machines and chuckers. Since the maturation of CNC, the implicit dichotomy of "manual versus automatic" still exists, but because CNC is so ubiquitous, the term "automatic" has lost some of its distinguishing power. All CNC machine tools are automatic, but the usage in the machining industries does not routinely call them by that term. The term "automatic", when it is used at all, still often refers implicitly to cam-operated machines. Thus a 2-axis CNC lathe is not referred to as an "automatic lathe" even if fully automated. Small- to medium-sized cam-operated automatic lathes are usually called screw machines or automatic screw machines. These machines work on parts that (as a rough guide only) are up to in
diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid f ...
and in length. Screw machines almost invariably do ''bar work'', meaning a length of
bar stock Bar stock, also (colloquially) known as blank, slug or billet, is a common form of raw purified metal, used by industry to manufacture metal parts and products. Bar stock is available in a variety of extrusion shapes and lengths. The most common ...
passes through the spindle and is gripped by the chuck (usually a collet chuck). As the part is being machined, the entire length of bar stock is rotated with the spindle. When the part is done, it is 'parted' from the bar, the chuck in released, the bar fed forward, and the chuck closed again, ready for the next cycle. The bar-feeding can happen by various means, including pulling-finger tools that grab the bar and pull or roller bar feed that pushes the bar from behind. Larger cam-operated automatic lathes are usually called automatic chucking lathes, automatic lathes, automatic chuckers, automatics, or chuckers. The 'chucker' part of the name comes from the workpieces being discrete blanks, held in a bin called a "magazine", and each one takes a turn at being chucked and machined. (This is analogous to the way that each round of ammunition in the magazine of a
semi-automatic pistol A semi-automatic pistol is a type of repeating single-chamber handgun ( pistol) that automatically cycles its action to insert the subsequent cartridge into the chamber (self-loading), but requires manual actuation of the trigger to actu ...
gets its turn at being chambered.) The blanks are either individual forgings or castings, or they are pre- sawn pieces of
billet A billet is a living-quarters to which a soldier is assigned to sleep. Historically, a billet was a private dwelling that was required to accept the soldier. Soldiers are generally billeted in barracks or garrisons when not on combat duty, alth ...
. However, some members of this family of machine tools turn bar work or work on centers (e.g., the Fay automatic lathe). Regarding bar work of large diameter (for example, or more), it is merely an academic point whether it is called "screw machine work" or just "automatic work".


Screw machine

Screw machines, being the class of automatic lathes for small- to medium-sized parts, are used in the high-volume manufacture of a vast variety of turned components. During the Swiss screw machining process, the workpiece is supported with a guide bushing, near the cutting tool.


Screw machine nomenclature

Speaking with reference to the normal definition of the term ''screw machine'', all screw machines are fully automated, whether mechanically (via cams) or by CNC, which means that once they are set up and started, they continue running and producing parts with little human intervention. Mechanical automation came first, beginning in the 1870s; computerized control (via first NC and then CNC) came later, beginning in the 1950s. The name ''screw machine'' is somewhat of a
metonym Metonymy () is a figure of speech in which a concept is referred to by the name of something closely associated with that thing or concept. Etymology The words ''metonymy'' and ''metonym'' come from grc, μετωνυμία, 'a change of name' ...
, as screw machines can make parts other than
screw A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to ...
s or that are not threaded. However, the archetypal use for which screw machines were named was screw-making. The definition of the term ''screw machine'' has changed with changing technology. Any use of the term prior to the 1840s, if it occurred, would have referred ad hoc to any machine tool used to produce screws. That is, there would have been no established differentiation from the term '' screw-cutting lathe''. When turret lathes were developed in the 1840s, the term ''screw machine'' was applied to them in overlapping usage with the term ''turret lathe''. In 1860, when some of the movements, such as turret indexing, were mechanically automated, the term ''automatic screw machine'' was applied, and the term ''hand screw machine'' or ''manual screw machine'' was
retronym A retronym is a newer name for an existing thing that helps differentiate the original form/version from a more recent one. It is thus a word or phrase created to avoid confusion between older and newer types, whereas previously (before there were ...
ously applied to the earlier machines. Within 15 years, the entire part-cutting cycle had been mechanically automated, and machines of the 1860 type were retronymously called ''semi-automatic''. From that time on, machines with fully automated cycles were usually called ''automatic screw machines'', and eventually, in the usage of most people in the machining industries, the term ''screw machine'' no longer was used to refer to manual or semi-automatic turret lathes, having become reserved for one class of machine, the fully mechanically automated type. This narrow meaning of ''screw machine'' remained stable from about the 1890s until the 1950s. ( Brown & Sharpe continued to call some of their hand-operated turret lathe models "screw machines", but most machinists reserved the term for automatics.) Within this class called ''screw machines'' there were variations, such as single- spindle versus multispindle, horizontal-turret versus vertical-turret, etc. With the advent of NC, screw machines diverged into two classes, mechanical and NC. This distinction continues today with mechanical screw machines and CNC screw machines. However, in shop-floor jargon, the term ''screw machine'' by itself is still often understood in context to imply a mechanical screw machine, so the retronym ''mechanical screw machine'' is not consistently used.


Automatic chucker

An automatic chucking machine is similar to an automatic screw machine; both use spindles in production. The use of spindles, which are able to drill, bore and cut the workpiece, allows several functions simultaneously on both machines. A key difference between the machines is that the automatic chucker handles larger work, which due to its size is more often chucking work and less often bar work. The Fay automatic lathe was a variant that specialized in turning work on centers. While a screw machine is limited to around practice, automatic chuckers are available that can handle up to chucks. The chucks are air-operated. Many of these machines are multispindle (more than one main spindle). Well-known brands of such machines have included National-Acme, Hardinge, New Britain, New Britain-Gridley, Acme-Gridley, Davenport, Bullard Mult-Au-Matic (a vertical multispindle variant), and Thomas Ryder and Son. Automatic chuckers are a class of machine tool specialized to narrow industry niches, such as OEM part suppliers to the
automotive industry The automotive industry comprises a wide range of companies and organizations involved in the design, development, manufacturing, marketing, and selling of motor vehicles. It is one of the world's largest industries by revenue (from 16 % ...
. They are limited in their economic niches to high-volume production of large parts, which tends to occur only at relatively few companies (compared to smaller work that may be done by small businesses). The market for such machine tools does not generally include local job shops or tool and die shops. Cam-operated chuckers are fading into history faster than most other non-CNC machine tool classes. This is because the few companies that have them tend to be forced to continually adapt to the latest state of the art (today all CNC) to compete and survive. Cam-op chuckers may be more likely to be scrapped than other types of non-CNC machine tools. Unlike with "Grandpa's South Bend lathe" or "Dad's old
Bridgeport Bridgeport is the most populous city and a major port in the U.S. state of Connecticut. With a population of 148,654 in 2020, it is also the fifth-most populous in New England. Located in eastern Fairfield County at the mouth of the Pequonn ...
knee mill", virtually no one can afford to keep and use them for sentimental reasons alone. As with most nondigital commercial
typesetting Typesetting is the composition of text by means of arranging physical ''type'' (or ''sort'') in mechanical systems or '' glyphs'' in digital systems representing '' characters'' (letters and other symbols).Dictionary.com Unabridged. Random ...
machinery (such as Linotype machines).


Choice of machines and control type

Mechanical screw machines have been replaced to some extent by CNC lathes (turning centers) and CNC screw machines. However, they are still commonly in operation, and for high-volume production of turned components it is still often true that nothing is as cost-efficient as a mechanical screw machine. In the hierarchy of manufacturing machines, the screw machine sits at the top when large product volumes are needed. An engine lathe sits at the bottom, taking the least time to set up but the most skilled labor and time to actually produce a part. A turret lathe has traditionally been one step above an engine lathe, needing greater set-up time but being able to produce a higher volume of product and usually requiring a lower-skilled operator once the set-up process is complete. Screw machines may require an extensive set-up, but once they are running, a single operator can monitor the operation of several machines. The advent of the CNC lathe (or more properly, CNC turning center) has blurred these distinct levels of production to some extent. The CNC turning center most appropriately fits in the mid-range of production, replacing the turret lathe. However, it is often possible to produce a single component with a CNC turning center more quickly than can be done with an engine lathe. To some extent too, the CNC turning center has stepped into the region traditionally occupied by the (mechanical) screw machine. CNC screw machines do this to an even greater degree, but they are expensive. In some cases they are vital, yet in others a mechanical machine can match or beat overall performance and profitability. It is not unusual for cam-op automatic lathes to beat CNCs on cycle time. CNC offers many benefits, not least CAD/CAM integration, but the CNC itself usually does not give any inherent speed advantage within the context of an automatic lathe cycle in terms of
speeds and feeds The phrase speeds and feeds or feeds and speeds refers to two separate velocities in machine tool practice, cutting speed and feed rate. They are often considered as a pair because of their combined effect on the cutting process. Each, however, ...
or tool-changing speed. There are many variables involved in answering the question of which is best for a particular part at a particular company. ( Overhead is part of the calculation—not least because most cam-op machines are long since paid for, whereas a late-model CNC machine has hefty monthly payments). Businesses relying on cam-op machines are still
competing Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indivi ...
even in today's CNC-filled environment; they just need to be vigilant and smart about keeping it that way. In the multispindle segment, some
machine tool builder A machine tool builder is a corporation or person that builds machine tools, usually for sale to manufacturers, who use them to manufacture products. A machine tool builder runs a machine factory, which is part of the machine industry. The machin ...
s also build hybrid machines that are part CNC and part old-school control (some stations are CNC while others are cam-op or actuated with simple hydraulic cycles). This lets shops with certain mixes of work derive competitive advantage from the lower cost compared with all-CNC machines. The variety of machines that allow profitable production within certain niches reflects the variety of work that exists: some high-volume work remains the province of cam-op; full CNC with all the bells and whistles outcompetes on some flexible low-volume work; and hybrid machines may yield the lowest unit price on mixes in between.


Design

An automatic lathe may have a single spindle or multiple spindles. Each spindle contains a bar or blank of material that is being machined simultaneously. A common configuration is six spindles. The cage that holds these six bars of material indexes after each machining operation is complete. The indexing is reminiscent of a
Gatling gun The Gatling gun is a rapid-firing multiple-barrel firearm invented in 1861 by Richard Jordan Gatling. It is an early machine gun and a forerunner of the modern electric motor-driven rotary cannon. The Gatling gun's operation centered on a c ...
. Each station may have multiple tools that cut the material in sequence. The tools are usually arranged in several axes, such as turret (rotary indexing), horizontal slide (linear indexing), and vertical slide (linear indexing). The linear groups are called "gangs". The operation of all these tools is similar to that on a turret lathe. By way of example: a bar of material is fed forward through the spindle. The face of the bar is machined (facing operation). The outside of the bar is machined to shape (
turning Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates. Usually the term "turning" is reserved for the generation ...
operation). The bar is
drill A drill is a tool used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driver chuck. Hand-operated types are dramatically decreasing in popularity and cordless battery-powered ones proliferating due to ...
ed or
bored In conventional usage, boredom, ennui, or tedium is an emotional and occasionally psychological state experienced when an individual is left without anything in particular to do, is listlessness and dissatisfaction arising from a lack of occup ...
, and finally, the part is cut off (parting operation). In a single-spindle machine, these four operations would most likely be performed sequentially, with four cross-slides each coming into position in turn to perform their operation. In a multi-spindle machine, each station corresponds to a stage in the production sequence through which each piece is then cycled, all operations occurring simultaneously, but on different pieces of work, in the manner of an
assembly line An assembly line is a manufacturing process (often called a ''progressive assembly'') in which parts (usually interchangeable parts) are added as the semi-finished assembly moves from workstation to workstation where the parts are added in se ...
.


Operations


Form tools

For the machining of complex shapes, it is common to use form tools. This contrasts with the cutting that is performed on an engine lathe where the cutting tool is usually a single-point tool. A form tool has the form or contour of the final part but in reverse, so it cuts the material leaving the desired component shape. This contrasts to a single-point tool, which cuts on one point at a time and the shape of the component is dictated by the motion of the tool rather than its shape.


Threading

Unlike on a lathe, single-point threading is rarely if ever performed; it is too time-consuming for the short cycle times that are typical of screw machines. A self-releasing
die head A die head is a threading die that is used in the high volume production of threaded fasteners. Die heads are commonly used on lathes A lathe () is a machine tool that rotates a workpiece about an axis of rotation to perform various op ...
can rapidly cut or roll-form threads on outside diameters. A non-releasing tap holder with a tap can quickly cut inside diameters but it requires single spindle machines to reverse into high speed in order for the tap to be removed from the work. Threading and tapping speed (low speed) is typically 1/5 the high speed.


Rotary broaching

Rotary broaching is another common operation. The broach holder is mounted stationary while its internal live spindle and end cutting broach tool are driven by the workpiece. As the broach is fed into or around the workpiece, the broach's contact points are constantly changing, easily creating the desired form. The most common form made this way is a hexagonal socket in the end of a cap screw.


History

The history of automatic lathes in industrial contexts began with screw machines, and that history can only be truly understood within the context of screw making in general. Thus the discussion below begins with a simple overview of screw making in prior centuries, and how it evolved into 19th-, 20th-, and 21st-century practice. Humans have been making screws since ancient times. For most of those centuries, screw making generally involved custom cutting of the threads of each screw by hand (via whittling or filing). Other ancient methods involved wrapping
wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is co ...
around a mandrel (such as a stick or metal rod) or carving a tree branch that had been spirally wrapped by a vine. Various machine elements that potentially lent themselves to screw making (such as the
lathe A lathe () is a machine tool that rotates a workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, and turning, with tools that are applied to the workpiece ...
, the
leadscrew A leadscrew (or lead screw), also known as a power screw or translation screw,Bhandari, p. 202. is a screw used as a linkage in a machine, to translate turning motion into linear motion. Because of the large area of sliding contact between ...
, the slide rest,
gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic ...
s, slide rests geared direct to spindles, and "change gear" gear trains) were developed over the centuries, with some of those elements being quite ancient. Various sparks of inventive power during the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
and
Renaissance The Renaissance ( , ) , from , with the same meanings. is a period in European history marking the transition from the Middle Ages to modernity and covering the 15th and 16th centuries, characterized by an effort to revive and surpass ide ...
combined some of these elements into screw-making machines that presaged the industrial era to follow. For example, various medieval inventors whose names are lost to history clearly worked on the problem, as shown by Wolfegg Castle's ''Medieval Housebook'' (written circa 1475–1490),. and
Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially rested on ...
and Jacques Besson left us with drawings of screw-cutting machines from the 1500s; not all of these designs are known to have been built, but clearly similar machines were a reality during Besson's lifetime. However, it was not until 1760–1800. that these various elements were brought together successfully to create (in contemporaneous parallel) two new types of machine tool: the screw-cutting lathe (for low-volume, toolroom-style production of ''machine'' screws, with easy selection of various pitches) and the first high-volume-production, specialized, single-purpose machine tools for the production of screws, which were created to produce ''wood'' screws eaning screws made of metal for use in woodat high volume and low
unit price A product's average price is the result of dividing the product's total sales revenue by the total units sold. When one product is sold in variants, such as bottle sizes, managers must define "comparable" units. Average prices can be calculated b ...
. Screw-cutting lathes fed into the just-dawning evolution of modern
machine shop A machine shop or engineering workshop (UK) is a room, building, or company where machining, a form of subtractive manufacturing, is done. In a machine shop, machinists use machine tools and cutting tools to make parts, usually of metal or pla ...
practice, whereas the wood-screw-making machines fed into the just-dawning evolution of the modern hardware industry, that is, the concept of one factory supplying the needs of thousands of customers, who consumed screws in growing quantities for
carpentry Carpentry is a skilled trade and a craft in which the primary work performed is the cutting, shaping and installation of building materials during the construction of buildings, ships, timber bridges, concrete formwork, etc. Carpenters t ...
, cabinet making, and other trades, but did not make the hardware themselves (purchasing it instead from capital-intensive specialist makers for lower unit cost than they could achieve on their own). These two classes of machine tools simultaneously took the various classes of screws and moved them, for the first time, from the category of expensive, hand-made, seldom-used objects into the category of affordable, often- interchangeable
commodity In economics, a commodity is an economic good, usually a resource, that has full or substantial fungibility: that is, the market treats instances of the good as equivalent or nearly so with no regard to who produced them. The price of a co ...
. (The interchangeability developed gradually, from intra-company to inter-company to national to international). Between 1800 and 1840, on the machine-screw side, it became common practice to build all of the relevant screw-cutting machine elements into engine lathes, so the term "screw-cutting lathe" ceased to stand in contradistinction to other metalworking lathe types as a "special" kind of lathe. Meanwhile, on the wood-screw side, hardware manufacturers had developed for their own in-house use the first fully automatic echanically automatedspecial-purpose machine tools for the making of screws.. The 1760–1840 development arc was a tremendous technological advance, but later advancements would make screws even cheaper and more prevalent yet again. These began in the 1840s with the adaptation of the engine lathe with a turret-head toolholder to create the turret lathe. This development greatly reduced the time, effort, and skill needed from the machine operator to produce each machine screw. Single-pointing was forgone in favor of
die head A die head is a threading die that is used in the high volume production of threaded fasteners. Die heads are commonly used on lathes A lathe () is a machine tool that rotates a workpiece about an axis of rotation to perform various op ...
cutting for such medium- and high-volume repetitive production. Then, in the 1870s, the turret lathe's part-cutting cycle (sequence of movements) was automated by being put under cam control, in a way very similar to how music boxes and
player piano A player piano (also known as a pianola) is a self-playing piano containing a pneumatic or electro-mechanical mechanism, that operates the piano action via programmed music recorded on perforated paper or metallic rolls, with more modern im ...
s can play a tune automatically. According to Rolt (1965),. the first person to develop such a machine was
Christopher Miner Spencer Christopher Miner Spencer (June 20, 1833 – January 14, 1922) was an American inventor, from Manchester, Connecticut, who invented the Spencer repeating rifle, one of the earliest models of lever-action rifle, a steam powered "horseless car ...
, a
New England New England is a region comprising six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York to the west and by the Canadian provinces ...
inventor. Charles Vander Woerd may have contemporarily independently invented a machine similar to Spencer's. However, the wood-screw-making machines of the 1840s and 1850s pecial-purpose factory production machine tools as opposed to small-machine-shop machine tools such as those developed by Cullen Whipple of the New England Screw Company and Thomas J. Sloan of the American Screw Company, had anticipated the machines of Spencer and Vander Woerd in various ways, albeit approaching the problem of automated screw production from a different commercial angle. All of the above machine tools (i.e., screw-cutting lathes; suitably equipped engine lathes and bench lathes; turret lathes; turret-lathe-derived screw machines; and wood-screw-factory screw machines) were sometimes called "screw machines" during this era (logically enough, given that they were machines tailored to screw making). The nomenclatural evolution whereby the term "screw machine" is often used more narrowly than that is discussed above. Spencer patented his idea in 1873; but his patent failed to protect the cam drum, which Spencer called the 'brain wheel'. Therefore, many other people quickly took up the idea. Later important developers of fully automatic lathes included S. L. Worsley, who developed a single-spindle machine for Brown & Sharpe, Edwin C. Henn, Reinhold Hakewessel, and George O. Gridley, who developed multiple-spindle variants and who was involved with a succession of corporations (Acme, National, National-Acme, Windsor Machine Company, Acme-Gridley, New Britain-Gridley);.. Edward P. Bullard Jr, who led the development of the Bullard Mult-Au-Matic; F.C. Fay and Otto A. Schaum, who developed the Fay automatic lathe;. Ralph Flanders and his brother Ernest, who further refined the Fay lathe and developed the automatic screw thread grinder. Meanwhile, engineers in Switzerland were also developing new manually and automatically controlled lathes. The technological developments in America and Switzerland flowed rapidly into other industrialized countries (via routes such as machine tool
export An export in international trade is a good produced in one country that is sold into another country or a service provided in one country for a national or resident of another country. The seller of such goods or the service provider is a ...
s; trade journal articles and advertisements;
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, from
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s to regional events; and the turnover and
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of engineers, setup hands, and operators). There, local innovators also developed further tooling for the machines and built clone machine models. The development of numerical control was the next major leap in the history of automatic lathes—and it is also what changed the paradigm of what the "manual versus automatic" distinction meant. Beginning in the 1950s, NC lathes began to replace manual lathes and cam-op screw machines, although the displacement of the older technology by CNC has been a long, gradual arc that even today is not a total eclipse. By the 1980s, true CNC screw machines (as opposed to simpler CNC lathes), Swiss-style and non-Swiss, had begun to make serious inroads into the realm of cam-op screw machines. Similarly, CNC chuckers were developed, eventually evolving even into CNC
rotary transfer machine A rotary transfer machine is a machine tool, typically for metal working Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and divers ...
s. These machine tools are little known outside the automotive manufacturing sector.


References


Bibliography

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External links


YouTube video showing a 1965 cam-op screw machine in action.

YouTube video showing another cam-op screw machine.
{{Machine and metalworking tools Automatic lathes