The most basic concept in multiaxis machining is understanding the CNC machine’s Universe. There are many individual coordinate systems in that Universe, representing Machine Home Position, Tool Change Position, Nesting Positions (also known as Local Coordinate Systems), Machine Rotary Zero Position and more. These coordinate systems exist in 3D space and are often also rotated around the machines rotary or pivoting axes.
Most newcomers have a problem navigating this Universe and quickly get disoriented. When navigating new territories a steady point of reference is needed – a beacon marking a known position.
Our own Universe doesn’t have a known center, but all CNC machines have their own center of Universe, known as a Machine Home Position. This is the location to which the all the machine axes move when a machine is powered up and ‘Zero Return’ is performed. Machinists talk about all machines as if the machine was a living person (female) they would say: “first you must send the machine home”. They don’t mean that the machine walked home, they mean that the machine’s axes traveled to their respective zero location. At this Home Position all machine’s axes position displays read Zero. This is the Absolute Machine Coordinate Systems Origin. This is the machines center of Universe.
All additional coordinate systems live in this Universe. The Tool Change Location is a relative distance from here. Any time you indicate a new face and location and then save it as your Local Coordinate system it will be saved in the machine’s registry as a position and orientation in the Machine’s Absolute Coordinate System. The Machines Rotary Zero Point is the intersection point of the rotary and pivoting axes, this position is also an exact position in this Universe. Knowing the exact location and orientation of the workpiece relative to MRZP is essential for accurate operation and programming any multiaxis equipment.