Computer Numerical Control (CNC) is one of the technologies used to control a machining operation via computer program. Most commonly used key computerized machine tools available in the industry are CNC Turning (Lathe) machine and CNC Milling machine. CNC helps to improve productivity by increasing the speed machine parts are produced, provides uniform quality across all products, better finishing by providing accuracy in dimensions, reduce complexity in manufacturing complex parts and reduce scrap. Drawback with CNC are huge initial investment and need for highly skilled operator to manage the system. Coordinate system is used for shaping metals, the cutting tool should move in contact with the work piece at certain specific points, while the work piece or cutting tool is rotating. Two types of Coordinate systems are Cartesian and Polar.
Cartesian coordinate system is used to describe the position of a 2D or 3D point in space. In Polar coordinate system a point is located by its distance to the point of origin and its angle to a specified axis. CNC Lathe Machine’s coordinate system is used to ensure that machine is able to read the assigned coordinates correctly to indicate the position of the work piece. Key parts of the system are
- Machine Zero point (M)
- Work piece Zero Point (W)
Machine Zero Point is the origin of the coordinate system which is defined by the manufacturer. They can't be changed. It is located in the center of the work spindle nose for CNC lathes. Work piece zero point is the origin of the work part based coordinate system. Its location is specified by the programmer.
CNC Turning machine has at least 2 controllable feed axes. When the cutting tool moves toward and backward the machine spindle, this is called movement along Z axis. When the cutting tool moves in cross direction to the longitudinal axis of the work piece, this is called movement along X axis. Positive Z direction is when the tool moves away from the work piece in Z axis. Positive X direction is when the tool moves away from the work part in X axis. The provision of a C-axis unit in a CNC Lathe converts the CNC lathe in to a TURN MILL center. Both turning and milling can be done in the same CNC lathe and this arrangement completely eliminates the use of a separate milling machine. To machine a work piece we need a technical drawing on which we should illustrate the required dimensions to make the required shape. To dimension the work piece we need to specify a certain point on it, from which we should take the measurement is called origin point. The origin point on the work piece is called Work piece zero point (W).