Modern CNC systems have many coordinate systems. One of them is a machine coordinate system. It is determined by the sensors of the base and for each machine it is unchanged, i.e. the origin is fixed at some physical point on the machine. It is accepted that the zero point of machine coordinates is the base point of the machine (at which the sensors are triggered), but this is not a mandatory requirement. For the machine zero point, you can set any offset relative to the base sensors (see home search parameters). Moreover, the machine may not be equipped with home sensors at all. In this case, the operator manually brings the axes to the desired position and resets the machine coordinates of the axes at this point (simulating the operation of the home sensors).
When preparing the G-Code in the CAM system, it is convenient to set the zero point relative to the workpiece, and, often, it is not known exactly where the workpiece will be located on the machine desktop. Therefore, the concept of a working coordinate system is introduced. Before starting the execution of the G-Code, the CNC system must specify where the working zero relative to the machine zero is located. In this case, the control system remembers the offset of the working zero relative to the machine.
There can be several working coordinate systems and they can be switched with codes G54-G59. The offset of each of them relative to machine zero is stored in non-volatile memory and the next time it starts, it will be automatically restored after the homing operation (see. Why do I need to do a homing?). If the search for the home is not done, then the working zero offset will still be restored, but so far the current machine coordinate is conditionally unknown, then the working one is also incorrect. Thus, the main advantage of the operation “homing” is the accurate restoration of the working coordinates of the machine after turning off the power, which allows you to easily continue long-term processing in the next work shift.
Why use multiple coordinate systems?
Consider, for example, a milling machine, on the work table of which there is a vise, a rotary axis and directly in the table there are several mounting holes, the machine coordinates of which are known. In this case, it is convenient to place the zero of one of the coordinate systems in the center of rotation of the rotary axis, the second somewhere in the center of the vise field, and the third in one of the mounting holes. In this case, after each search for the base, these coordinate systems will restore their position. Now, when preparing the G-Code in the CAM system, you just need to specify where the working zero will be located, depending on which of the methods of fastening the workpiece, the G-Code is made.