Turret lathe
Encyclopedia
Lathe (metal)
A metal lathe or metalworking lathe is a large class of lathes designed for precisely machining relatively hard materials. They were originally designed to machine metals; however, with the advent of plastics and other materials, and with their inherent versatility, they are used in a wide range of...
that is used for repetitive production of duplicate parts, which by the nature of their cutting process are usually interchangeable
Interchangeable parts
Interchangeable parts are parts that are, for practical purposes, identical. They are made to specifications that ensure that they are so nearly identical that they will fit into any device of the same type. One such part can freely replace another, without any custom fitting...
. It evolved from earlier lathes with the addition of the turret, which is an indexable
Indexing (motion)
Indexing in reference to motion is moving into a new position or location quickly and easily but also precisely. After a machine part has been indexed, its location is known to within a few hundredths of a millimeter , or often even to within a few thousandths of a millimeter , despite the fact...
toolholder that allows multiple cutting operations to be performed, each with a different cutting tool, in easy, rapid succession, with no need for the operator to perform setup tasks in between, such as installing or uninstalling tools, nor to control the toolpath. The latter is due to the toolpath's being controlled by the machine, either in jig
Jig (tool)
In metalworking and woodworking, a jig is a type of tool used to control the location and/or motion of another tool. A jig's primary purpose is to provide repeatability, accuracy, and interchangeability in the manufacturing of products. A jig is often confused with a fixture; a fixture holds the...
-like fashion, via the mechanical limits placed on it by the turret's slide and stops, or via electronically-directed servomechanism
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
s for computer numerical control (CNC) lathes.
Overview
There are many variants of the turret lathe. They can be most generally classified by size (small, medium, or large); method of control (manual, automated mechanically, or automated via computer (numerical control (NC) or computer numerical control (CNC)); and bed orientation (horizontal or vertical).The archetypical turret lathe: horizontal, manual
The archetypical turret lathe, and the first in order of historical appearance, is the horizontal-bed, manual turret lathe. The term "turret lathe" without further qualification is still understood to refer to this type. The formative decades for this class of machine were the 1840s through 1860s, when the basic idea of mounting an indexable turret on a bench lathe or engine lathe was born, developed, and disseminated from the originating shops to many other factories. Some important tool-builders in this development were Stephen Fitch; Gay, Silver & Co.; Elisha K. RootElisha K. Root
Elisha K. Root was a Connecticut machinist and inventor.Root was born on a Massachusetts farm and worked as a bobbin boy in a cotton mill before switching, at the age of 15, to working in a machine shop in Ware, Massachusetts. At age 24 he was hired by Connecticut industrialist Samuel W...
of Colt
Colt's Manufacturing Company
Colt's Manufacturing Company is a United States firearms manufacturer, whose first predecessor corporation was founded in 1836 by Sam Colt. Colt is best known for the engineering, production, and marketing of firearms over the later half of the 19th and the 20th century...
; J.D. Alvord of the Sharps Armory
Sharps Rifle Manufacturing Company
Sharps Rifle Manufacturing Company was the manufacturer of Sharps Rifle. It was organized by Samuel Robbins and Richard S. Lawrence as a holding company in Hartford, Connecticut on October 9, 1851 with $100,000 in capital. John C. Palmer was president, Christian Sharps an engineer, and Richard S....
; Frederick W. Howe, Richard S. Lawrence, and Henry D. Stone of Robbins & Lawrence; J.R. Brown of Brown & Sharpe
Brown & Sharpe
Brown & Sharpe is a division of Hexagon Metrology, Inc., a multinational corporation focused mainly on metrological tools and technology. During the 19th and 20th centuries, Brown & Sharpe was one of the most well-known and influential firms in the machine tool industry...
; and Francis A. Pratt
Francis A. Pratt
Francis Ashbury Pratt was a Connecticut mechanical engineer, inventor, and co-founder of Pratt & Whitney.Pratt was born in Peru, New York. In the early 1850s, he designed a milling machine for George S...
of Pratt & Whitney
Pratt & Whitney
Pratt & Whitney is a U.S.-based aerospace manufacturer with global service operations. It is a subsidiary of United Technologies Corporation . Pratt & Whitney's aircraft engines are widely used in both civil aviation and military aviation. Its headquarters are in East Hartford, Connecticut, USA...
. Various designers at these and other firms later made further refinements.
Semi-automatic turret lathes
Sometimes machines similar to those above, but with power feeds and automatic turret-indexing at the end of the return stroke, are called "semi-automatic turret lathes". This nomenclature distinction is blurry and not consistently observed. The term "turret lathe" encompasses them all. During the 1860s, when semi-automatic turret lathes were developed, they were sometimes called "automatic". What we today would call "automatics", that is, fully automatic machines, had not been developed yet. During that era both manual and semi-automatic turret lathes were sometimes called "screw machines", although we today reserve that term for fully automatic machines.Automatic turret lathes
During the 1870s through 1890s, the mechanically automated "automatic" turret lathe was developed and disseminated. These machines can execute many part-cutting cycles without human intervention. Thus the duties of the operator, which were already greatly reduced by the manual turret lathe, were even further reduced, and productivity increased. These machines use camCam
A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path...
s to automate the sliding and indexing of the turret and the opening and closing of the chuck
Chuck (engineering)
A chuck is a specialized type of clamp used to hold an object, usually an object with radial symmetry, especially a cylindrical object. It is most commonly used to hold a rotating tool or a rotating workpiece...
. Thus, they execute the part-cutting cycle somewhat analogously to the way in which an elaborate cuckoo clock
Cuckoo clock
A cuckoo clock is a clock, typically pendulum-regulated, that strikes the hours with a sound like a common cuckoo's call and typically has a mechanical cuckoo that emerges with each note...
performs an automated theater show. Small- to medium-sized automatic turret lathes are usually called "screw machine
Screw machine
A screw machine may refer to a:* Screw machine , a small- to medium-sized automatic lathe that is mechanically automated via cams...
s" or "automatic screw machines", while larger ones are usually called "automatic chucking lathes", "automatic chuckers", or "chuckers".
Machine tools of the "automatic" variety, which in the pre-computer era meant mechanically automated, had already reached a highly advanced state by World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
.
Computer numerical control and second-operation lathes
When World War IIWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
ended, the digital computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
was poised to develop from a colossal laboratory curiosity into a practical technology that could begin to disseminate into business and industry. The advent of electronics-based automation in machine tools via numerical control
Numerical control
Numerical control refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to controlled manually via handwheels or levers, or mechanically automated via cams alone...
(NC) and then computer numerical control (CNC) displaced to a large extent, but not at all completely, the previously existing manual and mechanically automated machines. Today, most CNC lathes have turrets, and so could logically be called "turret lathes", but the terminology is usually not used that way. Horizontal CNC lathes, with or without turrets, are generally called "CNC lathes" or "CNC turning centers" or "turning centers", and the term "turret lathe" by itself is still usually understood in context to refer to horizontal, manual turret lathes. The changed role in the production process that such machines now play is reflected in another name for them, second-operation lathe, as explained later.
Vertical turret lathes
The term "vertical turret lathe" (VTL) is applied to machines wherein the same essential design of the horizontal version is upended, which allows the headstock to sit on the floor and the faceplateLathe faceplate
A lathe faceplate is the basic workholding accessory for a wood or metal turning lathe. It is a circular metal plate which fixes to the end of the lathe spindle...
to become a horizontal rotating table, analogous to a huge potter's wheel
Potter's wheel
In pottery, a potter's wheel is a machine used in asma of round ceramic ware. The wheel may also be used during process of trimming the excess body from dried ware and for applying incised decoration or rings of color...
. This is useful for the handling of very large, heavy, short workpieces. Vertical lathes in general are also called "vertical boring mills" or often simply "boring mills"; therefore a vertical turret lathe is a vertical boring mill equipped with a turret. A CNC version is called a "CNC VTL".
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Capstan versus turret
The term "capstan lathe" overlaps in sense with the term "turret lathe" to a large extent. In many times and places, it has been understood to be synonymSynonym
Synonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...
ous with "turret lathe". In other times and places it has been held in technical contradistinction to "turret lathe", with the difference being in whether the turret's slide is fixed to the bed (ram-type turret) or slides on the bed's ways (saddle-type turret). The difference in terminology is mostly a matter of United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and Commonwealth
Commonwealth of Nations
The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-four independent member states...
usage versus United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
usage. American usage tends to call them all "turret lathes".
The word "capstan" could logically seem to refer to the turret itself, and to have been inspired by the nautical capstan
Capstan (nautical)
A capstan is a vertical-axled rotating machine developed for use on sailing ships to apply force to ropes, cables, and hawsers. The principle is similar to that of the windlass, which has a horizontal axle.- History :...
. A lathe turret with tools mounted in it can very much resemble a nautical capstan full of handspike
Handspike
A handspike is a metal bar or pipe that is used as a lever for prying or leverage, similar to a crowbar.Handspike is also an archaic term for a bar or lever, generally of wood, used in a windlass or capstan, for heaving anchor, and, in modified forms, for various other purposes....
s. This interpretation would lead Americans to treat "capstan" as a synonym of "turret" and "capstan lathe" as a synonym of "turret lathe". However, the multi-spoked handles that the operator uses to advance the slide are also called capstans, and they themselves also resemble the nautical capstan.
No distinction between "turret lathe" and "capstan lathe" persists upon translation from English into other languages. Most translations involve the term "revolver", and serve to translate either of the English terms.
The words "turret" and "tower", the former being a diminutive
Diminutive
In language structure, a diminutive, or diminutive form , is a formation of a word used to convey a slight degree of the root meaning, smallness of the object or quality named, encapsulation, intimacy, or endearment...
of the latter, come ultimately from the Latin "turris", which means "tower", and the use of "turret" both to refer to lathe turrets and to refer to gun turret
Gun turret
A gun turret is a weapon mount that protects the crew or mechanism of a projectile-firing weapon and at the same time lets the weapon be aimed and fired in many directions.The turret is also a rotating weapon platform...
s seems certainly to have been inspired by its earlier connection to the turret
Turret
In architecture, a turret is a small tower that projects vertically from the wall of a building such as a medieval castle. Turrets were used to provide a projecting defensive position allowing covering fire to the adjacent wall in the days of military fortification...
s of fortified
Fortification
Fortifications are military constructions and buildings designed for defence in warfare and military bases. Humans have constructed defensive works for many thousands of years, in a variety of increasingly complex designs...
buildings and to siege tower
Siege tower
A siege tower is a specialized siege engine, constructed to protect assailants and ladders while approaching the defensive walls of a fortification. The tower was often rectangular with four wheels with its height roughly equal to that of the wall or sometimes higher to allow archers to stand on...
s. The history of the rook in chess is connected to the same history, with the French word for rook, tour, meaning "tower".
It is an interesting coincidence that the word "tour" in French can mean both "lathe" and "tower", with the first sense coming ultimately from Latin "tornus", "lathe", and the second sense coming ultimately from Latin "turris", "tower". "Tour revolver", "tour tourelle", and "tour tourelle revolver" are various ways to say "turret lathe" in French.
Flat-turret lathe
A subtype of horizontal turret lathe is the flat-turret lathe. Its turret is flat (and analogous to a rotary tableRotary table
A rotary table is a precision work positioning device used in metalworking. It enables the operator to drill or cut work at exact intervals around a fixed axis...
), allowing the turret to pass beneath the part. Patented by James Hartness
James Hartness
James Hartness was an American inventor; a mechanical engineer; an entrepreneur who mentored other inventors to develop their machine tool products and create a thriving industrial center in southeastern Vermont; an amateur astronomer who fostered the construction of telescopes by amateurs in his...
of Jones & Lamson, and first disseminated in the 1890s, it was developed to provide more rigidity via requiring less overhang in the tool setup, especially when the part is relatively long.
Hollow-hexagon turret lathe
Hollow-hexagon turret lathes competed with flat-turret lathes by taking the conventional hexagon turret and making it hollow, allowing the part to pass into it during the cut, analogously to how the part would pass over the flat turret. In both cases, the main idea is to increase rigidity by allowing a relatively long part to be turned without the tool overhang that would be needed with a conventional turret, which is not flat or hollow.Monitor lathe
The term "monitor lathe" formerly (1860s-1940s) referred to the class of small- to medium-sized manual turret lathes used on relatively small work. The name was inspired by the monitor-class warshipsMonitor (warship)
A monitor was a class of relatively small warship which was neither fast nor strongly armoured but carried disproportionately large guns. They were used by some navies from the 1860s until the end of World War II, and saw their final use by the United States Navy during the Vietnam War.The monitors...
, which the monitor lathe's turret resembled. Today, lathes of such appearance, such as the Hardinge
Hardinge, Inc.
Hardinge, Inc. is a machine tool manufacturer with global headquarters in Elmira, New York, USA. It began operation in 1890. Hardinge is best known for its lathes, both non-CNC and CNC....
DSM-59 and its many clones, are still common, but the name "monitor lathe" is no longer current in the industry.
Toolpost turrets and tailstock turrets
Turrets can be added to non-turret lathes (bench lathes, engine lathes, toolroom lathes, etc.) by mounting them on the toolpost, tailstock, or both. Often these turrets are not as large as a turret lathe's, and they usually do not offer the sliding and stopping that a turret lathe's turret does; but they do offer the ability to index through successive tool settings.Mid-19th century: do not treat duplicate parts like one-off parts
The development of the turret lathe around the middle of the 19th century was a key aspect of the advancement of manufacturing technology. Unlike bench lathes, engine lathes, and toolroom lathes, on which each tool change involved some amount of setup, and toolpath had to be carefully controlled by the operator, turret lathes allowed the multiple tool changes and toolpaths of one part-cutting cycle to be repeated with little time or effort. By taking the tool-changing and the toolpath control out of the hands of the operator and building it into the machine tool, it accomplished several feats: it made interchangeable parts easier, faster, and thus cheaper to produce; and it made their production possible by workers with little skill. As long as a few skilled engineerEngineer
An engineer is a professional practitioner of engineering, concerned with applying scientific knowledge, mathematics and ingenuity to develop solutions for technical problems. Engineers design materials, structures, machines and systems while considering the limitations imposed by practicality,...
s, toolmakers
Tool and die maker
Tool and die makers are workers in the manufacturing industry who make jigs, fixtures, dies, molds, machine tools, cutting tools , gauges, and other tools used in manufacturing processes...
, and setup technicians made and equipped the machine correctly, just about any operator could be hired (inexpensively) to run it.
Another way to look at this change is that humans gradually figured out that they should not treat duplicate parts like one-off parts. You do not need a master craftsman to cut each duplicate part as if it were unique; if you can set up a repeatable sequence of restricted movements, you can simply repeat the same sequence with each part. And if you can preserve the setting of each tool, so that a tool change does not destroy the setting, but rather lets it be indexed back into position whenever needed, then you have saved vast amounts of time and effort.
The ideas above developed gradually, first in the armory
Armory (military)
An armory or armoury is a place where arms and ammunition are made, maintained and repaired, stored, issued to authorized users, or any combination of those...
practice of the mid and late 19th century (otherwise known as the American system
American system of manufacturing
The American system of manufacturing was a set of manufacturing methods that evolved in the 19th century. It involved semi-skilled labor using machine tools and jigs to make standardized, identical, interchangeable parts, manufactured to a tolerance, which could be assembled with a minimum of time...
), and then in true mass production
Mass production
Mass production is the production of large amounts of standardized products, including and especially on assembly lines...
during the 20th century. Those two phenomena have not always been differentiated from each other, but the difference is in the degree to which toolpath control had replaced skilled fitting, or, as it is more often expressed, the degree to which "the skill had been built into the machine tool". The replacement did not happen overnight, but rather was a gradual tapering off of reliance upon fitting, the progress varying by plant and by decade, until it had been completely eliminated from the assembly process, creating true mass production.
Late-19th through mid-20th centuries: key to mass production
From the late-19th through mid-20th centuries, turret lathes, both manual and automatic (i.e., screw machines and chuckers), were one of the most important classes of machine toolMachine tool
A machine tool is a machine, typically powered other than by human muscle , used to make manufactured parts in various ways that include cutting or certain other kinds of deformation...
s for mass production
Mass production
Mass production is the production of large amounts of standardized products, including and especially on assembly lines...
.
Mid-20th century to present: transition to small runs and second operations
With the development and dissemination of CNC lathes, which themselves often have automated turrets, manual turret lathes began to lose their position as the key to mass production of turned parts. However, they did not become obsolete; the focus of their use simply shifted from the main turning operations of mass production, which are now usually done by CNCs, to small runs, for which they can still compete in unit cost with CNC use, and second operations, such as re-chucking a part turned out by a CNC in order to make a few simple cuts on the back. This transition in primary job description is reflected in the name "second-operation lathe", which is often synonymous with "manual turret lathe". Similarly, cam-operated screw machines and chuckers did not disappear; they simply shifted to a different niche. They still often compete with CNC machines in terms of unit cost per part produced, depending on the difference in overhead. A CNC lathe with hefty payments may translate to higher overall costs than a screw machine or chucker that is long since paid for.Description of an example part-cutting cycle on a manual turret lathe
By pushing the handlever of a manual turret forward, the tool is moved via the turret's slide toward the workpiece being held by the chuckChuck (engineering)
A chuck is a specialized type of clamp used to hold an object, usually an object with radial symmetry, especially a cylindrical object. It is most commonly used to hold a rotating tool or a rotating workpiece...
, soon making contact and cutting or forming the part. On the return stroke, the tool is retracted and then indexed
Indexing (motion)
Indexing in reference to motion is moving into a new position or location quickly and easily but also precisely. After a machine part has been indexed, its location is known to within a few hundredths of a millimeter , or often even to within a few thousandths of a millimeter , despite the fact...
to the next tool held in the turret. In this way, a sequence of operations can be performed on a part without switching tools with each operation. That is, different tools can be shifted into position without the need to unscrew one and screw in another. Each tool can be set for a different length of travel by a stop screw located at the far right of the turret.
As an example, if one wanted to make a batch of special knurled
Knurling
Knurling is a manufacturing process, typically conducted on a lathe, whereby a visually attractive diamond-shaped pattern is cut or rolled into metal.- Uses :...
-head screw
Screw
A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...
s, the turret could be set up with tools and used in this sequence:
- Stop to set length of bar stock to be machined;
- Box tool to turn diameter of stock down to threading size;
- Geometric die head to cut external threadsScrew threadA screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...
on turned-down part, - Knurling tool to knurl the screw's head.
After this, a front tool on the cross slide could cut a groove in the knurled area, providing a chamfer
Chamfer
A chamfer is a beveled edge connecting two surfaces. If the surfaces are at right angles, the chamfer will typically be symmetrical at 45 degrees. A fillet is the rounding off of an interior corner. A rounding of an exterior corner is called a "round" or a "radius"."Chamfer" is a term commonly...
, and then a rear tool would be brought forward to cut the finished screw from the bar, called "parting it off".
External links
- YouTube video showing example cycle on a manual turret lathe, narrated by operator
- YouTube video showing the movement of the turrets and the taking of various cuts on a CNC vertical turret lathe
- YouTube video showing the movement of the turret and the taking of various cuts on a manual engine lathe retrofitted with a CNC turret