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Numerical control
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A CNC turning center
Numerical control (NC) is theautomation 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. 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. Theseearly servomechanisms were rapidly augmented with analog and digital computers, creating the modern computer numerical control (CNC) machine tools that have revolutionized the machining processes.
In modern CNC systems, end-to-end component design is highly automated using computer-aided design (CAD) and computer-aided manufacturing (CAM) programs. The programs produce a computer file that isinterpreted 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 controllerand 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.
Contents [hide]  * 1 History * 1.1 Earlier forms of automation * 1.1.1 Cams * 1.1.2 Tracer control * 1.2 Servos and selsyns *1.3 Parsons and Sikorsky * 1.4 Punch cards and first tries at NC * 1.5 Enter MIT * 1.6 MIT's machine * 1.7 Proliferation of NC * 1.8 CNC arrives * 1.9 CAD meets CNC * 1.10 Proliferation of CNC * 1.11 DIY, hobby, and personal CNC * 1.12 Today * 2 Description * 2.1 Tools with CNC variants * 3 Tool / machine crashing * 4 Numerical accuracy vsEquipment backlash * 5 See also * 6 Notes * 7 References * 8 Further reading * 9 External links |
[edit] History
[edit] Earlier forms of automation
[edit] Cams

Siemens CNC panel.
The automation of machine tool control began in the 19th century with cams that "played" a machine tool in the way that cams had long been playing musical boxes or operating elaborate cuckoo clocks. ThomasBlanchard built his gun-stock-copying lathes (1820s–30s), and the work of people such as Christopher Miner Spencer developed the turret lathe into the screw machine (1870s). Cam-based automation had already reached a highly advanced state by World War I (1910s).
However, automation via cams is fundamentally different from numerical control because it cannot be abstractly programmed. Cams canencode information, but getting the information from the abstract level of an engineering drawing into the cam is a manual process that requires sculpting and/or machining and filing.
Various forms of abstractly programmable control had existed during the 19th century: those of the Jacquard loom, player pianos, and mechanical computers pioneered by Charles Babbage and others. These developments hadthe potential for convergence with the automation of machine tool control starting in that century, but the convergence did not happen until many decades later.
[edit] Tracer control
The application of hydraulics to cam-based automation resulted in tracing machines that used a stylus to trace a template, such as the enormous Pratt & Whitney "Keller Machine", which could copy templates...