CNC stands for computer numeric control. When the tools and machines are controlled by the computers in the manufacturing system, the system is called computer numeric control. The various machines e.g. lathe, mill, metal cutting machine etc. can be equipped with CNC and advancement ca be provided. CNC provides automation in the machine tools.

The programing language are used in computers through which the control is established. The commands are given to the tool. The path of the tool and position will be provided to the computer through programming and the machine tool will perform accordingly.

Initially it was known as NC (numeric control). The operation was controlled by numeric signals in the system. The use of NC system started in 40’s decade. After the development of computers, the NC system is provided the advancement with computers and programing language are added in the system. The automation becomes easier and then the system is given the name computer numeric control (CNC). 

In the CNC machines the tool is allowed to move in different axes. Stepper motor and servomechanisms are used to move in different direction i.e. linear or angular. The precision offered by the CNC is very high as compare to conventional machine. This is due to numeric control. The process like welding, cutting, machining, drilling etc. can be performed with high quality and high efficiency.


If a part is to be manufactured by CNC machine. The first thing we need is the engineering drawing of the part. The drawing should be well labeled so that any dimensional error can be eliminated. Then the cad program would be developed according to that drawing. In the programming of CNC G-code and M-code is used. These code specifies the movement of tool and guide the system to perform the operation. In the programming the position, path, co-ordinates, speed and other essential factors will be inserted with the help of G-codes and M-codes. The path is about the different positions of the tool where the operations are performed. At the time of programming, the care should be taken. Wrong programming can cause fatal accident because of wrong movement of tool.

G - CODE and M – CODE: - G-code and M-codes are the elements of programming in CNC.


G codes are used to provide the information to the system about motion, speed, axes etc. it is also called G programming language. This tells the system that how the task will be completed. The path of the tool is determined, the speed of the machine is defined and various positions are defined for the operation. The plane on which the tool ill move is decided. Some examples are given below.

  • G00 – for the straight line movement of tool.
  • G03 – for anticlockwise circular movement.
  • G17 – to select the XY plane.
  • G28 – to return at its initial position.


M codes are used for miscellaneous functions. These codes are used for non-machining operations. Generally ON/OFF types of operations are performed through M codes. It is aid to the G codes to perform the operations easily. Some examples of M codes are given below

  • M02 – to end the program
  • M06 – to change the tool
  • M09 – to stop the coolant supply


  1. Repeatability of the CNC machines is very good i.e. accurate part can be produced repeatedly.
  2. The high precision is most important advantage of using CNC. It can produce lo tolerances and higher precision parts than conventional machining methods.
  3. Multiple operation can be performed at the same time by using multiple tools simultaneously.
  4. Parts with complex design can be produced.
  5. Higher rate of production can be achieved by using CNC instead of using manual machining.