Computer Numerical Control (CNC) is the automated control of machine tools with the use of a computer.  It actually originated from "numerical control", or NC, which refers to a form of machine automation done in the 1940's to 1950's, prior to the use of computers for such a purpose. 

NC uses programmed commands that are stored on a medium such as paper tape to automate the motion of the tools.  The tools in an NC machine are moved by motors that follow the programmed commands fed into it. When computers became the controller of such systems in the 1970's, the term "NC" was replaced by "CNC".

Modern CNC systems can design and manufacture a product from start to finish through its built-in computer-aided-design and computer-aided manufacturing (CAD/CAM) capabilities.  CAD/CAM programs can read product design files and produce the designed product automatically by utilizing its arsenal of tools.

With its ability to easily cut curves or mill complex 3-D structures, CNC machines revolutionized the design and manufacturing industries and resulted in products that were not manufacturable before.  CNC machines also reduced the number of workers needed to fabricate a product and shortened manufacturing cycle times.  Because of these benefits, CNC machines soon proliferated in factories around the world.

There are a wide variety of CNC machines in the industry.  Some are dedicated to a specific machining task, while others incorporate a whole range of tooling capabilities. Small CNC machines for hobbyists at home are also available now - thanks to continuously decreasing costs of computer and electromechanical hardware.

Figure 1.  An example of a modern CNC machine

                  

A typical CNC milling machine has a table that moves in the Y-axis and a tool chuck that moves in the X and Z axes.  The positions of the table and the tool are controlled by a system of motors and gears that produce the precise movements needed to work on the work piece and produce a final product that resembles the design. Complex CNC machines are now housed in large cabinets to protect its operators from accidents as well as shield its operations. 

  

Tools that have CNC versions or have been incorporated into CNC systems include the following: drills, lathes, milling machines, wood routers, electrical discharge machining (EDM) tools, welders, turret punches, hot wire foam cutters, plasma cutters, water jet cutters, laser cutters, surface grinders, etc.

  

    

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