The CNC lathe origin is the reference point adjusted by the machine tool manufacturer, and the specific position of the machine tool origin is set by the machine tool manufacturer. The CNC system determines the specific position of the machine tool origin by returning it to the machine tool reference point, thereby establishing a correct machine tool coordinate system. This is the purpose of the CNC lathe returning the machine tool reference point. The relative coordinate value of a CNC lathe refers to the incremental coordinate value of the machine tool reference point moving from the machine tool origin to the machine tool reference point in a coordinate system with the machine tool origin as the coordinate origin (the offset value of each axis is 0); The coordinate value refers to the value of the reference point of the machine tool in the coordinate system with the machine tool origin as the coordinate origin (the offset value of each axis is 0). Mechanical coordinate value refers to the coordinate value of the machine tool reference point in the coordinate system with the machine tool reference point as the coordinate origin. Of course, the definition of the coordinate system varies among different machine tool manufacturers, and in practical application, it should be operated according to the machine tool manual provided by the machine tool manufacturer.

When the position detection device is an encoder, after the system is powered off, it relies on the encoder battery to provide power and remember the position changes of the machine tool after the power is off. When the system is powered on, the system exchanges data with the position detection device, and refreshes the data to make the coordinate values of the machine tool coordinate system consistent with the actual position of the machine tool. So when the position detection device is an encoder, the machine tool does not need to return to the machine tool reference point when starting up. If the position detection device is an incremental encoder, because the coordinate value memorized by the system is the position before the machine tool is powered off, it may not be consistent with the actual position of the machine tool. Therefore, the CNC lathe starting up of the incremental encoder position detection device must be operated by the machine tool reference point.