Block 5:
It sets the program zero on the work part. There are three major environments in programming that require an established mathematical relationship.
            Machine: machine tool and control system
            Part: Workpiece + Drawing + material
            Tool:  Holder + Cutting tool

Machine zero point:
It is also called as home position or machine reference point. It is the origin of a machine coordinate system. On all CNC machines, machine zero is located at the positive end of each axis travel range. Figure 7.2.2 shows the machining volume and various planes. The machine reference point is located at the end of positive ranges of X, Y and Z axes. Figure 7.2.3 and 7.2.4 provide the clear views of the machine reference point. Machine control unit (MCU) understands the dimensions provided with respect to the machine reference point. But the programmer is providing the dimensions on the drawings based on the local coordinate system i.e. part coordinate system.

Figure 7.2.2 machining volume and machine reference point

Figure 7.2.3 Top view of a vertical machine as viewed towards the table

Figure 7.2.4 Front view of a vertical machine as viewed from front