PRIME MOTIONWork coordinates
A machine has to answer two different questions, so it keeps two sets of numbers.
| Question | Answered by |
|---|---|
| Where am I in myself? Can I reach that? | Machine coordinates |
| Where am I on the workpiece? | Work coordinates |
Machine coordinates
Established by homing, and fixed until you home again. The machine's own protections live here — travel limits, soft limits, tool-change positions, park positions. Nothing you do to work coordinates disturbs them.
Work coordinates
Measured from work zero: the point on your material that the program calls X0 Y0 Z0. Every program you run is written in this system, because a program describes a part, not a machine.
The gap between the two origins is the work offset. Setting work zero is really recording that offset.
Why this is the thing that goes wrong
A program has no idea where your material is. It assumes someone has told the machine, and that someone is you. If work zero is set 10 mm from where you believe it is, the program will run perfectly and cut in the wrong place — the machine has no way to notice.
Z is the one that bites
X and Y being wrong usually spoils a part. Z being wrong breaks things — a cut that should skim the surface plunges through the work and into the table.
Z zero is also the one most easily disturbed, because it changes with every tool. A machine with a toolsetter can re-measure automatically; without one, re-set Z after every tool change.