Numerical control - AbsoluteAstronomy.com

Numerical control refers to the automation

Automation

Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization...

of machine tool

Machine 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 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. The first NC machines were built in the 1940s and 1950s, based on existing tools that were modified with motors that moved the controls to follow points fed into the system on punched tape

Punched tape

Punched tape or paper tape is an obsolete form of data storage, consisting of a long strip of paper in which holes are punched to store data...

. These early servomechanisms were rapidly augmented with analog and digital computers, creating the modern computer numerical control (CNC) machine tools that have revolutionized the machining

Machining

Conventional machining is a form of subtractive manufacturing, in which a collection of material-working processes utilizing power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to physical remove material to achieve a desired...

processes.

In modern CNC systems, end-to-end component design is highly automated using computer-aided design

Computer-aided design

Computer-aided design , also known as computer-aided design and drafting , is the use of computer technology for the process of design and design-documentation. Computer Aided Drafting describes the process of drafting with a computer...

(CAD) and computer-aided manufacturing

Computer-aided manufacturing

Computer-aided manufacturing is the use of computer software to control machine tools and related machinery in the manufacturing of workpieces. This is not the only definition for CAM, but it is the most common; CAM may also refer to the use of a computer to assist in all operations of a...

(CAM) programs. The programs produce a computer file that is interpreted to extract the commands needed to operate a particular machine via a postprocessor, and then loaded into the CNC machines for production. Since any particular component might require the use of a number of different tools-drills, saws, etc., modern machines often combine multiple tools into a single "cell". In other cases, a number of different machines are used with an external controller and human or robotic operators that move the component from machine to machine. In either case, the complex series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD design.

Cams

The automation of machine tool control began in the 19th century with cam

Cam

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 that "played" a machine tool in the way that cams had long been playing musical box

Musical box

A music box is a 19th century automatic musical instrument that produces sounds by the use of a set of pins placed on a revolving cylinder or disc so as to pluck the tuned teeth of a steel comb. They were developed from musical snuff boxes of the 18th century and called carillons à musique...

es or operating 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...

s. Thomas Blanchard

Thomas Blanchard

Thomas Blanchard was an American inventor who lived much of his life in Springfield, Massachusetts, where in 1819, he pioneered the assembly line style of mass production in America, and also invented the major technological innovation known as interchangeable parts. Blanchard worked, for much of...

built his gun-stock-copying lathes (1820s–30s), and the work of people such as Christopher Miner Spencer

Christopher Miner Spencer

Christopher Miner Spencer 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 carriage", and several other inventions...

developed the turret lathe

Turret lathe

The turret lathe is a form of metalworking lathe that is used for repetitive production of duplicate parts, which by the nature of their cutting process are usually interchangeable...

into the screw machine (1870s). Cam-based automation 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...

(1910s).

However, automation via cams is fundamentally different from numerical control because it cannot be abstractly programmed. Cams can encode information, but getting the information from the abstract level of an engineering drawing

Engineering drawing

An engineering drawing, a type of technical drawing, is used to fully and clearly define requirements for engineered items.Engineering drawing produces engineering drawings . More than just the drawing of pictures, it is also a language—a graphical language that communicates ideas and information...

into the cam is a manual process that requires sculpting and/or machining

Machining

and filing

File (tool)

A file is a metalworking and woodworking tool used to cut fine amounts of material from a workpiece. It most commonly refers to the hand tool style, which takes the form of a steel bar with a case hardened surface and a series of sharp, parallel teeth. Most files have a narrow, pointed tang at one...

.

Various forms of abstractly programmable control had existed during the 19th century: those of the Jacquard loom

Jacquard loom

The Jacquard loom is a mechanical loom, invented by Joseph Marie Jacquard in 1801, that simplifies the process of manufacturing textiles with complex patterns such as brocade, damask and matelasse. The loom is controlled by punched cards with punched holes, each row of which corresponds to one row...

, player piano

Player piano

A player piano is a self-playing piano, containing a pneumatic or electro-mechanical mechanism that operates the piano action via pre-programmed music perforated paper, or in rare instances, metallic rolls. The rise of the player piano grew with the rise of the mass-produced piano for the home in...

s, and mechanical computer

Mechanical computer

A mechanical computer is built from mechanical components such as levers and gears, rather than electronic components. The most common examples are adding machines and mechanical counters, which use the turning of gears to increment output displays...

s pioneered by Charles Babbage

Charles Babbage

Charles Babbage, FRS was an English mathematician, philosopher, inventor and mechanical engineer who originated the concept of a programmable computer...

and others. These developments had the potential for convergence

Technological convergence

Technological convergence is the tendency for different technological systems to evolve towards performing similar tasks. Convergence can refer to previously separate technologies such as voice , data , and video that now share resources and interact with each other synergistically.The rise of...

with the automation of machine tool control starting in that century, but the convergence did not happen until many decades later.

Tracer control

The application of hydraulics

Hydraulics

Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control,...

to cam-based automation resulted in tracing machines that used a stylus to trace a template, such as the enormous Pratt & Whitney

Pratt & Whitney Measurement Systems

Pratt & Whitney Measurement Systems is a multinational corporation that specializes in producing high-precision measuring instruments and systems.-History:...

"Keller Machine", which could copy templates several feet across. Another approach was "record and playback", pioneered at General Motors

General Motors

General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...

(GM) in the 1950s, which used a storage system to record the movements of a human machinist, and then play them back on demand. Analogous systems are common even today, notably the "teaching lathe" which gives new machinists a hands-on feel for the process. None of these were numerically programmable, however, and required a master machinist at some point in the process, because the "programming" was physical rather than numerical.

Servos and selsyns

One barrier to complete automation was the required tolerances of the machining process, which are routinely on the order of thousandths of an inch. Although connecting some sort of control to a storage device like punched cards was easy, ensuring that the controls were moved to the correct position with the required accuracy was another issue. The movement of the tool resulted in varying forces on the controls that would mean a linear input would not result in linear tool motion. The key development in this area was the introduction of the 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...

, which produced highly accurate measurement information. Attaching two servos together produced a selsyn, where a remote servo's motions were accurately matched by another. Using a variety of mechanical or electrical systems, the output of the selsyns could be read to ensure proper movement had occurred (in other words, forming a closed-loop

Control theory

Control theory is an interdisciplinary branch of engineering and mathematics that deals with the behavior of dynamical systems. The desired output of a system is called the reference...

control system).

The first serious suggestion that selsyns could be used for machining control was made by Ernst F. W. Alexanderson, a Swedish immigrant to the U.S. working at General Electric

General Electric

General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...

(GE). Alexanderson had worked on the problem of torque amplification that allowed the small output of a mechanical computer to drive very large motors, which GE used as part of a larger gun laying

Gun laying

Gun laying is the process of aiming an artillery piece, such as a gun, howitzer or mortar on land or at sea against surface or air targets. It may be laying for direct fire, where the gun is aimed similarly to a rifle, or indirect fire, where firing data is calculated and applied to the sights...

system for US Navy ships. Like machining, gun laying requires very high accuracy - fractions of a degree - and the forces during the motion of the gun turrets was non-linear. In November 1931 Alexanderson suggested to the Industrial Engineering Department that the same systems could be used to drive the inputs of machine tools, allowing it to follow the outline of a template without the strong physical contact needed by existing tools like the Keller Machine. He stated that it was a "matter of straight engineering development". However, the concept was ahead of its time from a business development perspective, and GE did not take the matter seriously until years later, when others had pioneered the field.

Parsons and Sikorsky

The birth of NC is generally credited to John T. Parsons

John T. Parsons

John T. Parsons pioneered numerical control for machine tools in the 1940s.These developments were done in collaboration with his employee Frank L. Stulen, who Parsons hired when he was head of the Rotary Wing Branch of the Propeller Lab at Wright-Patterson Air Force Base, in April 1946...

, a machinist and salesman at his father's machining company, Parsons Corp.

In 1942 he was told that helicopter

Helicopter

A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...

s were going to be the "next big thing" by the former head of Ford Trimotor

Ford Trimotor

The Ford Trimotor was an American three-engined transport plane that was first produced in 1925 by the companies of Henry Ford and that continued to be produced until June 7, 1933. Throughout its time in production, a total of 199 Ford Trimotors were produced...

production, Bill Stout. He called Sikorsky Aircraft

Sikorsky Aircraft

The Sikorsky Aircraft Corporation is an American aircraft manufacturer based in Stratford, Connecticut. Its parent company is United Technologies Corporation.-History:...

to inquire about possible work, and soon got a contract to build the wooden stringers

Longeron

In aircraft construction, a longeron or stringer or stiffener is a thin strip of wood, metal or carbon fiber, to which the skin of the aircraft is fastened. In the fuselage, longerons are attached to formers and run the longitudinal direction of the aircraft...

in the rotor blades. At the time, rotors were built in the same fashion as wing

Wing

A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...

s, consisting of a long tubular steel spar

Spar (aviation)

In a fixed-wing aircraft, the spar is often the main structural member of the wing, running spanwise at right angles to the fuselage. The spar carries flight loads and the weight of the wings whilst on the ground...

with stringers (or more accurately ribs

Rib (aircraft)

In an aircraft, ribs are forming elements of the structure of a wing, especially in traditional construction.By analogy with the anatomical definition of "rib", the ribs attach to the main spar, and by being repeated at frequent intervals, form a skeletal shape for the wing...

) set on them to provide the aerodynamic shape that was then covered with a stressed skin

Stressed skin

In mechanical engineering, stressed skin is a type of rigid construction, intermediate between monocoque and a rigid frame with a non-loaded covering:...

. The stringers for the rotors were built from a design provided by Sikorsky, which was sent to Parsons as a series of 17 points defining the outline. Parsons then had to "fill in" the dots with a French curve

French curve

A French curve is a template made out of metal, wood or plastic composed of many different curves. It is used in manual drafting to draw smooth curves of varying radii....

to generate an outline. A wooden jig was built up to form the outside of the outline, and the pieces of wood forming the stringer were placed under pressure against the inside of the jig so they formed the proper curve. A series of trusswork

Truss

In architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in...

members were then assembled inside this outline to provide strength.

After setting up production at a disused furniture factory and ramping up production, one of the blades failed and it was traced to a problem in the spar. As at least some of the problem appeared to stem from spot welding a metal collar on the stringer to the metal spar. The collar was built into the stringer during construction, then slid onto the spar and welded in the proper position. Parsons suggested a new method of attaching the stringers directly to the spar using adhesives, never before tried on an aircraft design.

That development led Parsons to consider the possibility of using stamped metal stringers instead of wood. These would not only be much stronger, but far easier to make as well, as they would eliminate the complex layup and glue and screw fastening on the wood. Duplicating this in a metal punch would require the wooden jig to be replaced by a metal cutting tool made of tool steel

Tool steel

Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion, their ability to hold a cutting edge, and/or their resistance to deformation at elevated temperatures...

. Such a device would not be easy to produce given the complex outline. Looking for ideas, Parsons visited Wright Field to see Frank Stulen, the head of the Propeller Lab Rotary Ring Branch. During their conversation, Stulen concluded that Parsons didn't really know what he was talking about. Parsons realized Stulen had reached this conclusion, and hired him on the spot. Stulen started work on 1 April 1946 and hired three new engineers to join him.

Stulen's brother worked at Curtis Wright Propeller, and mentioned that they were using punched card

Punched card

A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined positions...

calculators for engineering calculations. Stulen decided to adopt the idea to run stress calculations on the rotors, the first detailed automated calculations on helicopter rotors. When Parsons saw what Stulen was doing with the punched card machines, he asked Stulen if they could be used to generate an outline with 200 points instead of the 17 they were given, and offset each point by the radius of a mill cutting tool. If you cut at each of those points, it would produce a relatively accurate cutout of the stringer. This could cut the tool steel and then easily be filed down to a smooth template for stamping metal stringers.

Stullen had no problem making such a program, and used it to produce large tables of numbers that would be taken onto the machine floor. Here, one operator read the numbers off the charts to two other operators, one on each of the X- and Y- axes. For each pair of numbers the operators would move the cutting head to the indicated spot and then lower the tool to make the cut. This was called the "by-the-numbers method", or more technically, "plunge-cutting positioning".

Punch cards and first tries at NC

At that point Parsons conceived of a fully automated machine tool. With enough points on the outline, no manual working would be needed to clean it up. However, with manual operation the time saved by having the part more closely match the outline was offset by the time needed to move the controls. If the machine's inputs were attached directly to the card reader, this delay, and any associated manual errors, would be removed and the number of points could be dramatically increased. Such a machine could repeatedly punch out perfectly accurate templates on command. But at the time Parsons had no funds to develop his ideas.

When one of Parsons's salesmen was on a visit to Wright Field, he was told of the problems the newly formed US Air Force was having with new jet-powered designs. He asked if Parsons had anything to help them. Parsons showed Lockheed

Lockheed Corporation

The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1912 and later merged with Martin Marietta to form Lockheed Martin in 1995.-Origins:...

their idea of an automated mill, but they were uninterested. They decided to use 5-axis template copiers to produce the stringers, cutting from a metal template, and had already ordered the expensive cutting machine. But as Parsons noted:

Now just picture the situation for a minute. Lockheed had contracted to design a machine to make these wings. This machine had five axes of cutter movement, and each of these was tracer controlled using a template. Nobody was using my method of making templates, so just imagine what chance they were going to have of making an accurate airfoil shape with inaccurate templates.

Parson's worries soon came true, and Lockheed's protests that they could fix the problem eventually rang hollow. In 1949 the Air Force arranged funding for Parsons to build his machines on his own. Early work with Snyder Machine & Tool Corp proved the system of directly driving the controls from motors failed to give the accuracy needed to set the machine for a perfectly smooth cut. Since the mechanical controls did not respond in a linear fashion, you couldn't simply drive it with a given amount of power, because the differing forces meant the same amount of power would not always produce the same amount of motion in the controls. No matter how many points you included, the outline would still be rough.

Enter MIT

This was not an impossible problem to solve, but would require some sort of feedback system, like a selsyn, to directly measure how far the controls had actually turned. Faced with the daunting task of building such a system, in the spring of 1949 Parsons turned to Gordon S. Brown

Gordon S. Brown

Gordon Stanley Brown was a professor of electrical engineering at MIT. He originated many of the concepts behind automatic-feedback control systems and the numerical control of machine tools. From 1959 to 1968, he served as the dean of MIT's engineering school. With his former student Donald P...

's Servomechanisms Laboratory at MIT

MIT Laboratory for Information and Decision Systems

The MIT Laboratory for Information and Decision Systems is an interdisciplinary research laboratory of MIT, working on research in the areas of communications, control, and signal processing combining faculty from the School of Engineering, the Department of Aeronautics and Astronautics, the...

, which was a world leader in mechanical computing and feedback systems. During the war the Lab had built a number of complex motor-driven devices like the motorized gun turret systems for the Boeing B-29 Superfortress and the automatic tracking system for the SCR-584 radar. They were naturally suited to technological transfer

Technology transfer

Technology Transfer, also called Transfer of Technology and Technology Commercialisation, is the process of skill transferring, knowledge, technologies, methods of manufacturing, samples of manufacturing and facilities among governments or universities and other institutions to ensure that...

into a prototype of Parsons's automated "by-the-numbers" machine.

The MIT team was led by William Pease assisted by James McDonough. They quickly concluded that Parsons's design could be greatly improved; if the machine did not simply cut at points A and B, but instead moved smoothly between the points, then not only would it make a perfectly smooth cut, but could do so with many fewer points - the mill could cut lines directly instead of having to define a large number of cutting points to "simulate" a line. A three-way agreement was arranged between Parsons, MIT, and the Air Force, and the project officially ran from July 1949 to June 1950. The contract called for the construction of two "Card-a-matic Milling Machines", a prototype and a production system. Both to be handed to Parsons for attachment to one of their mills in order to develop a deliverable system for cutting stringers.

Instead, in 1950 MIT bought a surplus Cincinnati Milling Machine Company

Cincinnati Milling Machine Company

The Cincinnati Milling Machine Company is the name of a machine tool building company which was incorporated in 1889. The company was formed for the purpose of building and promoting an innovative new concept for a machine tool. The principals in forming the company were Frederick V. Geiger and...

"Hydro-Tel" mill of their own and arranged a new contract directly with the Air Force that froze Parsons out of further development. Parsons would later comment that he "never dreamed that anybody as reputable as MIT would deliberately go ahead and take over my project." In spite of the development being handed to MIT, Parsons filed for a patent on "Motor Controlled Apparatus for Positioning Machine Tool" on 5 May 1952, sparking a filing by MIT for a "Numerical Control Servo-System" on 14 August 1952. Parsons received US Patent 2,820,187 on 14 January 1958, and the company sold an exclusive license to Bendix

Bendix

- People :* Bendix Hallenstein - New Zealand businessman* Henry Bendix - fictional character from Wildstorm comics* John E. Bendix - American Civil War and New York Guard general* Max Bendix - American composer, conductor, violinist* Reinhard Bendix - sociologist...

. IBM

IBM

International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

, Fujitsu

Fujitsu

is a Japanese multinational information technology equipment and services company headquartered in Tokyo, Japan. It is the world's third-largest IT services provider measured by revenues....

and General Electric all took sub-licenses after having already started development of their own devices.

MIT's machine

MIT fit gears to the various handwheel inputs and drove them with roller chain

Roller chain

Roller chain or bush roller chain is the type of chain drive most commonly used for transmission of mechanical power on many kinds of domestic, industrial and agricultural machinery, including conveyors, wire and tube drawing machines, printing presses, cars, motorcycles, and simple machines like...

s connected to motors, one for each of the machine's three axes (X, Y, and Z). The associated controller consisted of five refrigerator-sized cabinets that, together, were almost as large as the mill they were connected to. Three of the cabinets contained the motor controllers, one controller for each motor, the other two the digital reading system.

Unlike Parsons's original punched card design, the MIT design used standard 7-track punch tape for input. Three of the tracks were used to control the different axes of the machine, while the other four encoded various control information. The tape was read in a cabinet that also housed six relay

Relay

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...

-based hardware register

Hardware register

In digital electronics, especially computing, a hardware register stores bits of information, in a way that all the bits can be written to or read out simultaneously.The hardware registers inside a central processing unit are called processor registers....

s, two for each axis. With every read operation the previously read point was copied into the "starting point" register, and the newly read one into the "ending point" register. The tape was read continually and the number in the registers incremented with each hole encountered in their control track until a "stop" instruction was encountered, four holes in a line.

The final cabinet held a clock that sent pulses through the registers, compared them, and generated output pulses that interpolated between the points. For instance, if the points were far apart the output would have pulses with every clock cycle, whereas closely spaced points would only generate pulses after multiple clock cycles. The pulses are sent into a summing register in the motor controllers, counting up by the number of pulses every time they were received. The summing registers were connected to a digital to analog converter that increased power to the motors as the count in the registers increased, making the controls move faster.

The registers were decremented by encoders attached to the motors and the mill itself, which would reduce the count by one for every one degree of rotation. Once the second point was reached the counter would hold a zero, the pulses from the clock would stop, and the motors would stop turning. Each 1 degree rotation of the controls produced a 0.0005 inch movement of the cutting head. The programmer could control the speed of the cut by selecting points that were closer together for slow movements, or further apart for rapid ones.

The system was publicly demonstrated in September 1952, appearing in that month's Scientific American
Scientific American
Scientific American is a popular science magazine. It is notable for its long history of presenting science monthly to an educated but not necessarily scientific public, through its careful attention to the clarity of its text as well as the quality of its specially commissioned color graphics...

. MIT's system was an outstanding success by any technical measure, quickly making any complex cut with extremely high accuracy that could not easily be duplicated by hand. However, the system was terribly complex, including 250 vacuum tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

s, 175 relays and numerous moving parts, reducing its reliability in a production environment. It was also very expensive, the total bill presented to the Air Force was $360,000.14 ($2,641,727.63 in 2005 dollars). Between 1952 and 1956 the system was used to mill a number of one-off designs for various aviation firms, in order to study their potential economic impact.

Proliferation of NC

The Air Force funding for the project ran out in 1953, but development was picked up by the Giddings and Lewis Machine Tool Co. In 1955 many of the MIT team left to form Concord Controls, a commercial NC company with Giddings' backing, producing the Numericord controller. Numericord was similar to the MIT design, but replaced the punch tape with a magnetic tape

Magnetic tape

Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...

reader that General Electric was working on. The tape contained a number of signals of different phases, which directly encoded the angle of the various controls. The tape was played at a constant speed in the controller, which set its half of the selsyn to the encoded angles while the remote side was attached to the machine controls. Designs were still encoded on paper tape, but the tapes were transferred to a reader/writer that converted them into magnetic form. The magtapes could then be used on any of the machines on the floor, where the controllers were greatly reduced in complexity. Developed to produce highly accurate dies for an aircraft skinning press, the Numericord "NC5" went into operation at G&L's plant at Fond du Lac, WI in 1955.

Monarch Machine Tool also developed a numerical controlled lathe, starting in 1952. They demonstrated their machine at the 1955 Chicago Machine Tool Show (predecessor of today's IMTS

International Manufacturing Technology Show

The International Manufacturing Technology Show , first held in Cleveland, Ohio in 1927., is a trade show that features industrial machinery and technology. It is the largest manufacturing technology trade show in North America....

), along with a number of other vendors with punched card or paper tape machines that were either fully developed or in prototype form. These included Kearney & Trecker’s Milwaukee-Matic II that could change its cutting tool under numerical control, a common feature on modern machines.

A Boeing report noted that "numerical control has proved it can reduce costs, reduce lead times, improve quality, reduce tooling and increase productivity.” In spite of these developments, and glowing reviews from the few users, uptake of NC was relatively slow. As Parsons later noted:

The NC concept was so strange to manufacturers, and so slow to catch on, that the US Army itself finally had to build 120 NC machines and lease them to various manufacturers to begin popularizing its use.

In 1958 MIT published its report on the economics of NC. They concluded that the tools were competitive with human operators, but simply moved the time from the machining to the creation of the tapes. In Forces of Production, Noble claims that this was the whole point as far as the Air Force was concerned; moving the process off of the highly unionized factory floor and into the un-unionized white collar

White-collar worker

The term white-collar worker refers to a person who performs professional, managerial, or administrative work, in contrast with a blue-collar worker, whose job requires manual labor...

design office. The cultural context of the early 1950s, a second Red Scare

Red Scare

Durrell Blackwell Durrell Blackwell The term Red Scare denotes two distinct periods of strong Anti-Communism in the United States: the First Red Scare, from 1919 to 1920, and the Second Red Scare, from 1947 to 1957. The First Red Scare was about worker revolution and...

with a widespread fear of a bomber gap

Bomber gap

The "bomber gap" was the unfounded belief in the Cold War-era United States that the Soviet Union had gained an advantage in deploying jet-powered strategic bombers. Widely accepted for several years, the gap was used as a political talking point in order to justify greatly increased defense spending...

and of domestic subversion

Subversion

Apache Subversion is a software versioning and a revision control system distributed under a free license. Developers use Subversion to maintain current and historical versions of files such as source code, web pages, and documentation...

, sheds light on this interpretation. It was strongly feared that the West would lose the defense production race to the Communists, and that syndicalist power was a path toward losing, either by "getting too soft" (less output, greater unit expense) or even by Communist sympathy and subversion within unions (arising from their common theme of empowering the working class).

CNC arrives

Many of the commands for the experimental parts were programmed "by hand" to produce the punch tapes that were used as input. During the development of Whirlwind

Whirlwind (computer)

The Whirlwind computer was developed at the Massachusetts Institute of Technology. It is the first computer that operated in real time, used video displays for output, and the first that was not simply an electronic replacement of older mechanical systems...

, MIT's real-time computer, John Runyon coded a number of subroutines to produce these tapes under computer control. Users could enter a list of points and speeds, and the program would calculate the points needed and automatically generate the punch tape. In one instance, this process reduced the time required to produce the instruction list and mill the part from 8 hours to 15 minutes. This led to a proposal to the Air Force to produce a generalized "programming" language for numerical control, which was accepted in June 1956.

Starting in September, Ross and Pople outlined a language for machine control that was based on points and lines, developing this over several years into the APT programming language

APT programming language

APT or Automatically Programmed Tool is a high-level computer programming language used to generate instructions for numerically controlled machine tools. Douglas T. Ross is considered by many to be the father of APT. APT is a language and system that makes numerically controlled manufacturing...

. In 1957 the Aircraft Industries Association (AIA) and Air Material Command at Wright-Patterson Air Force Base

Wright-Patterson Air Force Base

Wright-Patterson Air Force Base is a United States Air Force base in Greene and Montgomery counties in the state of Ohio. It includes both Wright and Patterson Fields, which were originally Wilbur Wright Field and Fairfield Aviation General Supply Depot. Patterson Field is located approximately...

joined with MIT to standardize this work and produce a fully computer-controlled NC system. On 25 February 1959 the combined team held a press conference showing the results, including a 3D machined aluminum ash tray that was handed out in the press kit

Press kit

A press kit, often referred to as a media kit in business environments, is a pre-packaged set of promotional materials of a person, company, or organization distributed to members of the media for promotional use...

.

Meanwhile, Patrick Hanratty was making similar developments at GE as part of their partnership with G&L on the Numericord. His language, PRONTO, beat APT into commercial use when it was released in 1958. Hanratty then went on to develop MICR magnetic ink characters that were used in cheque processing, before moving to General Motors to work on the groundbreaking DAC-1

DAC-1

DAC-1, for Design Augmented by Computer, was one of the earliest graphical computer aided design systems. Developed by General Motors, IBM was brought in as a partner in 1960 and the two developed the system and released it to production in 1963. It was publicly unveiled at the fall Joint Computer...

CAD system.

APT was soon extended to include "real" curves in 2D-APT-II. With its release, MIT reduced its focus on NC as it moved into CAD experiments. APT development was picked up with the AIA in San Diego, and in 1962, by Illinois Institute of Technology Research. Work on making APT an international standard started in 1963 under USASI X3.4.7, but many manufacturers of NC machines had their own one-off additions (like PRONTO), so standardization was not completed until 1968, when there were 25 optional add-ins to the basic system.

Just as APT was being released in the early 1960s, a second generation of lower-cost transistorized computers was hitting the market that were able to process much larger volumes of information in production settings. This reduced the cost of programming for NC machines and by the mid 1960s, APT runs accounted for a third of all computer time at large aviation firms.

CAD meets CNC

While the Servomechanisms Lab was in the process of developing their first mill, in 1953, MIT's Mechanical Engineering Department dropped the requirement that undergraduates take courses in drawing. The instructors formerly teaching these programs were merged into the Design Division, where an informal discussion of computerized design started. Meanwhile the Electronic Systems Laboratory, the newly rechristened Servomechanisms Laboratory, had been discussing whether or not design would ever start with paper diagrams in the future.

In January 1959, an informal meeting was held involving individuals from both the Electronic Systems Laboratory and the Mechanical Engineering Department's Design Division. Formal meetings followed in April and May, which resulted in the "Computer-Aided Design Project". In December 1959, the Air Force issued a one year contract to ESL for $223,000 to fund the project, including $20,800 earmarked for 104 hours of computer time at $200 per hour. This proved to be far too little for the ambitious program they had in mind, although their engineering calculation system, AED, was released in March 1965.

In 1959, General Motors started an experimental project to digitize, store and print the many design sketches being generated in the various GM design departments. When the basic concept demonstrated that it could work, they started the DAC-1 project with IBM to develop a production version. One part of the DAC project was the direct conversion of paper diagrams into 3D models, which were then converted into APT commands and cut on milling machines. In November 1963 a design for the lid of a trunk moved from 2D paper sketch to 3D clay prototype for the first time. With the exception of the initial sketch, the design-to-production loop had been closed.

Meanwhile, MIT's offsite Lincoln Labs was building computers to test new transistorized designs. The ultimate goal was essentially a transistorized Whirlwind known as TX-2

TX-2

The MIT Lincoln Laboratory TX-2 computer was the successor to the Lincoln TX-0 and was known for its role in advancing both artificial intelligence and human-computer interaction.- Specifications :...

, but in order to test various circuit designs a smaller version known as TX-0

TX-0

The TX-0, for Transistorized Experimental computer zero, but affectionately referred to as tixo , was an early fully transistorized computer and contained a then-huge 64K of 18-bit words of magnetic core memory. The TX-0 was built in 1955 and went online in 1956 and was used continually through the...

was built first. When construction of TX-2 started, time in TX-0 freed up and this led to a number of experiments involving interactive input and use of the machine's CRT

Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...

display for graphics. Further development of these concepts led to Ivan Sutherland

Ivan Sutherland

Ivan Edward Sutherland is an American computer scientist and Internet pioneer. He received the Turing Award from the Association for Computing Machinery in 1988 for the invention of Sketchpad, an early predecessor to the sort of graphical user interface that has become ubiquitous in personal...

's groundbreaking Sketchpad

Sketchpad

Sketchpad was a revolutionary computer program written by Ivan Sutherland in 1963 in the course of his PhD thesis, for which he received the Turing Award in 1988. It helped change the way people interact with computers...

program on the TX-2.

Sutherland moved to the University of Utah

University of Utah

The University of Utah, also known as the U or the U of U, is a public, coeducational research university in Salt Lake City, Utah, United States. The university was established in 1850 as the University of Deseret by the General Assembly of the provisional State of Deseret, making it Utah's oldest...

after his Sketchpad work, but it inspired other MIT graduates to attempt the first true CAD system. It was Electronic Drafting Machine

Digigraphics

Digigraphics was one of the first graphical computer aided design systems to go on sale. Originally developed at Itek on the PDP-1 as EDM , the efforts were purchased by Control Data Corporation and ported to their machines, along with a new graphics terminal to support it...

(EDM), sold to Control Data and known as "Digigraphics", which Lockheed used to build production parts for the C-5 Galaxy

C-5 Galaxy

The Lockheed C-5 Galaxy is a large military transport aircraft built by Lockheed. It provides the United States Air Force with a heavy intercontinental-range strategic airlift capability, one that can carry outsize and oversize cargos, including all air-certifiable cargo. The Galaxy has many...

, the first example of an end-to-end CAD/CNC production system.

By 1970 there were a wide variety of CAD firms including Intergraph

Intergraph

Intergraph Corporation is an American software development and services company. It provides enterprise engineering and geospatially powered software to businesses, governments, and organizations around the world. Intergraph operates through two divisions: Process, Power & Marine and Security,...

, Applicon

Applicon

Applicon, Incorporated was one of the first vendors of Computer Aided Design and Manufacturing systems. It was founded in 1969 in Bedford, Massachusetts. During the 1970s and early 1980s, the company had its headquarters and R&D facility in Burlington, MA, while their manufacturing facility was in...

, Computervision

Computervision

Computervision, Inc. was an early pioneer in turnkey Computer Aided Design and Manufacturing . Computervision was founded in 1969 by Marty Allen and Philippe Villers, and headquartered in Bedford, Massachusetts, USA. Its early products were built on a Data General Nova platform...

, Auto-trol Technology, UGS Corp. and others, as well as large vendors like CDC and IBM.

Proliferation of CNC

The price of computer cycles fell drastically during the 1960s with the widespread introduction of useful minicomputer

Minicomputer

A minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems...

s. Eventually it became less expensive to handle the motor control and feedback with a computer program than it was with dedicated servo systems. Small computers were dedicated to a single mill, placing the entire process in a small box. PDP-8

PDP-8

The 12-bit PDP-8 was the first successful commercial minicomputer, produced by Digital Equipment Corporation in the 1960s. DEC introduced it on 22 March 1965, and sold more than 50,000 systems, the most of any computer up to that date. It was the first widely sold computer in the DEC PDP series of...

's and Data General Nova

Data General Nova

The Data General Nova was a popular 16-bit minicomputer built by the American company Data General starting in 1969. The Nova was packaged into a single rack mount case and had enough power to do most simple computing tasks. The Nova became popular in science laboratories around the world, and...

computers were common in these roles. The introduction of the microprocessor

Microprocessor

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

in the 1970s further reduced the cost of implementation, and today almost all CNC machines use some form of microprocessor to handle all operations.

The introduction of lower-cost CNC machines radically changed the manufacturing industry. Curves are as easy to cut as straight lines, complex 3-D structures are relatively easy to produce, and the number of machining steps that required human action have been dramatically reduced. With the increased automation of manufacturing processes with CNC machining, considerable improvements in consistency and quality have been achieved with no strain on the operator. CNC automation reduced the frequency of errors and provided CNC operators with time to perform additional tasks. CNC automation also allows for more flexibility in the way parts are held in the manufacturing process and the time required changing the machine to produce different components.

During the early 1970s the Western economies were mired in slow economic growth and rising employment costs, and NC machines started to become more attractive. The major U.S. vendors were slow to respond to the demand for machines suitable for lower-cost NC systems, and into this void stepped the Germans. In 1979, sales of German machines surpassed the U.S. designs for the first time. This cycle quickly repeated itself, and by 1980 Japan had taken a leadership position, U.S. sales dropping all the time. Once sitting in the #1 position in terms of sales on a top-ten chart consisting entirely of U.S. companies in 1971, by 1987 Cincinnati Milacron was in 8th place on a chart heavily dominated by Japanese firms.

Many researchers have commented that the U.S. focus on high-end applications left them in an uncompetitive situation when the economic downturn in the early 1970s led to greatly increased demand for low-cost NC systems. Unlike the U.S. companies, who had focused on the highly profitable aerospace market, German and Japanese manufacturers targeted lower-profit segments from the start and were able to enter the low-cost markets much more easily.

As computing and networking evolved, so did direct numerical control

Direct Numerical Control

Direct numerical control , also known as distributed numerical control , is a common manufacturing term for networking CNC machine tools...

(DNC). Its long-term coexistence with less networked variants of NC and CNC is explained by the fact that individual firms tend to stick with whatever is profitable, and their time and money for trying out alternatives is limited. This explains why machine tool models and tape storage media persist in grandfathered fashion even as the state of the art advances.

DIY, hobby, and personal CNC

Recent developments in small scale CNC have been enabled, in large part, by the Enhanced Machine Controller

Enhanced Machine Controller

Enhanced Machine Controller, or EMC2, is a FLOSS GNU/Linux software system to implement numerical control capability using general purpose computers to control machines...

project from the National Institute of Standards and Technology

National Institute of Standards and Technology

The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...

(NIST), an agency of the US Government's Department of Commerce. EMC is a public domain program operating under the Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

operating system and working on PC based hardware. After the NIST project ended, development continued, leading to EMC2 which is licensed under the GNU General Public License and Lesser GNU General Public License (GPL and LGPL). Derivations of the original EMC software have also led to several proprietary PC based programs notably TurboCNC, and Mach3, as well as embedded systems based on proprietary hardware. The availability of these PC based control programs has led to the development of DIY CNC, allowing hobbyists to build their own using open source hardware

Open source hardware

Open source hardware consists of physical artifacts of technology designed and offered in the same manner as free and open source software . Open source hardware is part of the open source culture movement and applies a like concept to a variety of components. The term usually means that...

designs. The same basic architecture has allowed manufacturers, such as Sherline and Taig, to produce turnkey lightweight desktop milling machines for hobbyists.

The easy availability of PC based software and support information of Mach3, written by Art Fenerty, lets anyone with some time and technical expertise make complex parts for home and prototype use. Fenerty is considered a principal founder of Windows-based PC CNC machining.

Eventually, the homebrew architecture was fully commercialized and used to create larger machinery suitable for commercial and industrial applications. This class of equipment has been referred to as Personal CNC. Parallel to the evolution of personal computers, Personal CNC has its roots in EMC and PC based control, but has evolved to the point where it can replace larger conventional equipment in many instances. As with the Personal Computer

Personal computer

A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...

, Personal CNC is characterized by equipment whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, often without professional training in CNC technology.

Today

Although modern data storage techniques have moved on from punch tape in almost every other role, tapes are still relatively common in CNC systems. Several reasons explain this. One is easy backward compatibility

Backward compatibility

In the context of telecommunications and computing, a device or technology is said to be backward or downward compatible if it can work with input generated by an older device...

of existing programs. Companies were spared the trouble of re-writing existing tapes into a new format. Another is the principle, mentioned earlier, that individual firms tend to stick with whatever is profitable, and their time and money for trying out alternatives is limited. A small firm that has found a profitable niche may keep older equipment in service for years because "if it ain't broke [profitability-wise], don't fix it." Competition

Competition (economics)

Competition in economics is a term that encompasses the notion of individuals and firms striving for a greater share of a market to sell or buy goods and services...

places natural limits on that approach, as some amount of innovation and continuous improvement eventually becomes necessary, lest competitors be the ones who find the way to the "better mousetrap".

One change that was implemented fairly widely was the switch from paper to mylar tapes, which are much more mechanically robust. Floppy disk

Floppy disk

A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...

s, USB flash drive

USB flash drive

A flash drive is a data storage device that consists of flash memory with an integrated Universal Serial Bus interface. flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g...

s and local area network

Local area network

A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...

ing have replaced the tapes to some degree, especially in larger environments that are highly integrated.

The proliferation of CNC led to the need for new CNC standards that were not encumbered by licensing or particular design concepts, like APT. A number of different "standards" proliferated for a time, often based around vector graphics markup languages supported by plotter

Plotter

A plotter is a computer printing device for printing vector graphics. In the past, plotters were widely used in applications such as computer-aided design, though they have generally been replaced with wide-format conventional printers...

s. One such standard has since become very common, the "G-code

G-code

G-code is the common name for the most widely used computer numerical control programming language, which has many implementations. Used mainly in automation, it is part of computer-aided engineering. G-code is sometimes called G programming language...

" that was originally used on Gerber Scientific

Gerber Scientific

Gerber Scientific Inc. , located in Tolland, Connecticut, is the parent of companies which provide end-to-end customer solutions to the world's sign making and specialty graphics, ophthalmic lens processing, and apparel and flexible materials industries. They also supply purpose-built software to...

plotters and then adapted for CNC use. The file format became so widely used that it has been embodied in an EIA

Electronic Industries Alliance

The Electronic Industries Alliance was a standards and trade organization composed as an alliance of trade associations for electronics manufacturers in the United States. They developed standards to ensure the equipment of different manufacturers was compatible and interchangeable...

standard. In turn, while G-code is the predominant language used by CNC machines today, there is a push to supplant it with STEP-NC

STEP-NC

STEP-NC is a machine tool control language that extends the ISO 10303 STEP standards with the machining model in ISO 14649, adding geometric dimension and tolerance data for inspection, and the STEP PDM model for integration into the wider enterprise...

, a system that was deliberately designed for CNC, rather than grown from an existing plotter standard.

While G-code is the most common method of programming, some machine-tool/control manufacturers also have invented their own proprietary "conversational" methods of programming, trying to make it easier to program simple parts and make set-up and modifications at the machine easier (such as Mazak's Mazatrol and Hurco). These have met with varying success.

A more recent advancement in CNC interpreters is support of logical commands, known as parametric programming (also known as macro programming). Parametric programs include both device commands as well as a control language similar to BASIC

BASIC

BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....

. The programmer can make if/then/else statements, loops, subprogram calls, perform various arithmetic, and manipulate variables to create a large degree of freedom within one program. An entire product line of different sizes can be programmed using logic and simple math to create and scale an entire range of parts, or create a stock part that can be scaled to any size a customer demands.

Since about 2006, the idea has been suggested and pursued to foster the convergence with CNC and DNC of several trends elsewhere in the world of information technology that have not yet much affected CNC and DNC. One of these trends is the combination of greater data collection (more sensors), greater and more automated data exchange

Data exchange

Data exchange is the process of taking data structured under a source schema and actually transforming it into data structured under a target schema, so that the target data is an accurate representation of the source data. Data exchange is similar to the related concept of data integration except...

(via building new, open

Open source

The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

industry-standard XML schema

XML schema

An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself...

s), and data mining

Data mining

Data mining , a relatively young and interdisciplinary field of computer science is the process of discovering new patterns from large data sets involving methods at the intersection of artificial intelligence, machine learning, statistics and database systems...

to yield a new level of business intelligence

Business intelligence

Business intelligence mainly refers to computer-based techniques used in identifying, extracting, and analyzing business data, such as sales revenue by products and/or departments, or by associated costs and incomes....

and workflow automation in manufacturing. Another of these trends is the emergence of widely published API

Application programming interface

An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...

s together with the aforementioned open data standards to encourage an ecosystem of user-generated apps and mashups

Mashup (web application hybrid)

In Web development, a mashup is a Web page or application that uses and combines data, presentation or functionality from two or more sources to create new services...

, which can be both open and commercial—in other words, taking the new IT culture of app marketplaces that began in web development and smartphone app development and spreading it to CNC, DNC, and the other factory automation systems that are networked with the CNC/DNC. MTConnect

MTConnect

MTConnect is a manufacturing industry standard to facilitate the organized retrieval of process information from numerically controlled machine tools. The initiative began as a result of lectures given by David Edstrom of Sun Microsystems and Dr...

is a leading effort to bring these ideas into successful implementation.

Description

Modern CNC mills differ little in concept from the original model built at MIT in 1952. Mills typically consist of a table that moves in the X and Y axes, and a tool spindle that moves in the Z (depth). The position of the tool is driven by motors through a series of step-down gears in order to provide highly accurate movements, or in modern designs, direct-drive stepper motor

Stepper

A stepper is a device used in the manufacture of integrated circuits that is similar in operation to a slide projector or a photographic enlarger. Steppers are an essential part of the complex process, called photolithography, that creates millions of microscopic circuit elements on the surface of...

or servo motors. Open-loop control works as long as the forces are kept small enough and speeds are not too great. On commercial metalworking machines closed loop controls are standard and required in order to provide the accuracy, speed, and repeatability demanded.

As the controller hardware evolved, the mills themselves also evolved. One change has been to enclose the entire mechanism in a large box as a safety measure, often with additional safety interlocks to ensure the operator is far enough from the working piece for safe operation. Most new CNC systems built today are completely electronically controlled.

CNC-like systems are now used for any process that can be described as a series of movements and operations. These include laser cutting

Laser cutting

Laser cutting is a technology that uses a laser to cut materials, and is typically used for industrial manufacturing applications, but is also starting to be used by schools, small businesses and hobbyists. Laser cutting works by directing the output of a high-power laser, by computer, at the...

, welding

Welding

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

, friction stir welding, ultrasonic welding

Ultrasonic welding

Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to workpieces being held together under pressure to create a solid-state weld. It is commonly used for plastics, and especially for joining dissimilar materials...

, flame and plasma cutting

Plasma cutting

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses using a plasma torch...

, bending, spinning, pinning, gluing, fabric cutting, sewing, tape and fiber placement, routing, picking and placing (PnP), and sawing.

Tools with CNC variants

Drill
Drill
A drill or drill motor is a tool fitted with a cutting tool attachment or driving tool attachment, usually a drill bit or driver bit, used for drilling holes in various materials or fastening various materials together with the use of fasteners. The attachment is gripped by a chuck at one end of...

s
EDMs
Electrical discharge machining
Electric discharge machining , sometimes colloquially also referred to as spark machining, spark eroding, burning, die sinking or wire erosion, is a manufacturing process whereby a desired shape is obtained using electrical discharges...
Lathes
Milling machine
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...

s
Wood routers
CNC wood router
A CNC wood router is a Numerical control tool that creates objects from wood. Parts of a project can be designed in the computer with a CAD/CAM program, and then cut automatically using a router to produce a finished part....
Sheet metal works
Sheet metal
Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material...

(Turret Punch)
Wire bending machines
Hot-wire foam cutter
Hot-wire foam cutter
A hot-wire foam cutter is a tool used to cut polystyrene foam and similar materials. The device consists of a thin, taut metal wire, often made of nichrome or stainless steel, or a thicker wire preformed into a desired shape, which is heated via electrical resistance to approximately 200°C...

s
Plasma cutters
Plasma cutting
Plasma cutting is a process that is used to cut steel and other metals of different thicknesses using a plasma torch...
Water jet cutter
Water jet cutter
A water jet cutter, also known as a waterjet, is a tool capable of slicing into metal or other materials using a jet of water at high velocity and pressure, or a mixture of water and an abrasive substance. The process is essentially the same as water erosion found in nature but greatly accelerated...

s
Laser cutting
Laser cutting
Laser cutting is a technology that uses a laser to cut materials, and is typically used for industrial manufacturing applications, but is also starting to be used by schools, small businesses and hobbyists. Laser cutting works by directing the output of a high-power laser, by computer, at the...
Oxy-fuel
Oxy-fuel welding and cutting
Oxy-fuel welding and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903...
Surface grinders
Cylindrical grinder
Cylindrical grinder
The cylindrical grinder is a type of grinding machine used to shape the outside of an object. The cylindrical grinder can work on a variety of shapes, however the object must have a central axis of rotation...

s
3D Printing
3D printing
3D printing is a form of additive manufacturing technology where a three dimensional object is created by laying down successive layers of material. 3D printers are generally faster, more affordable, and easier to use than other additive manufacturing technologies. However, the term 3D printing is...
Induction hardening
Induction hardening
Induction hardening is a form of heat treatment in which a metal part is heated by induction heating and then quenched. The quenched metal undergoes a martensitic transformation, increasing the hardness and brittleness of the part...

machines

Tool / machine crashing

In CNC, a "crash" occurs when the machine moves in such a way that is harmful to the machine, tools, or parts being machined, sometimes resulting in bending or breakage of cutting tools, accessory clamps, vises, and fixtures, or causing damage to the machine itself by bending guide rails, breaking drive screws, or causing structural components to crack or deform under strain. A mild crash may not damage the machine or tools, but may damage the part being machined so that it must be scrapped.

Many CNC tools have no inherent sense of the absolute position of the table or tools when turned on. They must be manually "homed" or "zeroed" to have any reference to work from, and these limits are just for figuring out the location of the part to work with it, and aren't really any sort of hard motion limit on the mechanism. It is often possible to drive the machine outside the physical bounds of its drive mechanism, resulting in a collision with itself or damage to the drive mechanism.

Many CNC tools also don't know anything about their working environment. They often lack any form of sensory capability to detect problems with the machining process, and will not abort if something goes wrong. They blindly follow the machining code provided and it is up to an operator to detect if a crash is either occurring or about to occur, and for the operator to manually abort the cutting process.

If the drive system is weaker than the machine structural integrity, then the drive system simply pushes against the obstruction and the drive motors "slip in place". The machine tool may not detect the collision or the slipping, so for example the tool should now be at 210mm on the X axis but is in fact at 32mm where it hit the obstruction and kept slipping. All of the next tool motions will be off by -178mm on the X axis, and all future motions are now invalid, which may result in further collisions with clamps, vises, or the machine itself. This is common in open loop stepper systems, but is not possible in closed loop systems unless mechanical slippage between the motor and drive mechanism has occurred. Instead, in a closed loop system, the machine will continue to attempt to move against the load until either the drive motor goes into an overcurrent condition or a servo following error alarm is generated.

Collision detection and avoidance is possible, through the use of absolute position sensors (optical encoder strips or disks) to verify that motion occurred, or torque sensors or power-draw sensors on the drive system to detect abnormal strain when the machine should just be moving and not cutting, but these are not a common component of most hobby CNC tools.

Instead, most hobby CNC tools simply rely on the assumed accuracy of stepper motors that rotate a specific number of degrees in response to magnetic field changes. It is often assumed the stepper is perfectly accurate and never mis-steps, so tool position monitoring simply involves counting the number of pulses sent to the stepper over time. An alternate means of stepper position monitoring is usually not available, so crash or slip detection is not possible.

Commercial CNC metalworking machines use closed loop feedback controls for axis movement. In a closed loop system, the control is aware of the actual position of the axis at all times. With proper control programming, this will reduce the possibility of a crash, but it is still up to the operator and tool path programmer to ensure that the machine is operated in a safe manner.

Numerical accuracy vs Equipment backlash

Within the numerical systems of CNC programming it is possible for the code generator to assume that the controlled mechanism is always perfectly accurate, or that accuracy tolerances are identical for all cutting or movement directions. This is not always a true condition of CNC tools.

CNC tools with a large amount of mechanical backlash

Backlash

A "backlash" is a popular negative reaction to something which has gained popularity, prominence, or influence. Although it can sometimes represent a categorical rejection of the idea, aesthetic, product, or fad in question, it is usually a reflection of a collective resentment of that thing's...

can still be highly accurate if the drive or cutting mechanism is only driven so as to apply cutting force from one direction, and all driving systems are pressed tight together in that one cutting direction. However a CNC device with high backlash and a dull cutting tool can lead to cutter chatter and possible workpiece gouging. Backlash also affects accuracy of some operations involving axis movement reversals during cutting, such as the milling of a circle, where axis motion is sinusoidal. However, this can be compensated for if the amount of backlash is precisely known by linear encoders or manual measurement.

The high backlash mechanism itself is not necessarily relied on to be repeatedly accurate for the cutting process, but some other reference object or precision surface may be used to zero the mechanism, by tightly applying pressure against the reference and setting that as the zero reference for all following CNC-encoded motions. This is similar to the manual machine tool method of clamping a micrometer

Micrometer

A micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...

onto a reference beam and adjusting the Vernier

Vernier

Vernier may refer to:Secondary adjustment devices for forms of "fine tuning":*Vernier scale on measuring instruments*Vernier thruster, on spacecraft*Vernier throttle, on aircraft*Vernier sight, on target riflesPeople:...

dial to zero using that object as the reference.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.