GlossaryKind of term: Manufacturing termWork origin
What is a work origin?
The work origin, or work zero, is the origin of the coordinate system in which the NC program describes positions on the workpiece.
Common choices are a corner of the block, the centre of a bore or the middle of a shaft's end face. It sits at a fixed distance from the machine zero. That distance is stored in the control as a work offset, on G-code controls for example under G54, on others in an offset or preset table. A setup usually has one; several parts or several tilt positions can call for more.
How is the work origin set?
The work origin is set during setup by probing with a spindle probe, with an edge finder or dial indicator, or by taking it over from a fixture or pallet on a zero-point system whose position is known. Which reference you choose depends on the datums on the drawing, the faces reachable and already machined in this setup, and the repeatability of the workholding. The setup sheet says which face, axis or bore is the reference and how to check it.
How does the work origin work in practice?
Setting the work origin is part of setup time, per setup and sometimes per piece. A probing cycle that runs for every piece moves that time into the cycle time. A fixture or zero-point system can make setting it per piece unnecessary. A wrong origin shifts features; a first-article check usually catches it, but without a check it can run through a whole batch. If the origin is taken from a face other than the drawing's datum, dimensions have to be converted and the working tolerance can get tighter, because the tolerance of the intermediate dimension counts.
What is the work origin often confused with?
The work origin is not the machine zero, which is fixed in the machine and does not change with the setup. It is not the datum either: the designer specifies the datum on the drawing, the manufacturing engineer or operator chooses the origin on the machine. Ideally they coincide, but that is a choice, not a given.
Frequently asked questions
Why put the work origin on the datum?
Because location and orientation tolerances, and often the dimensioning, refer to the datums. Take it from another face and you have to convert dimensions, with the intermediate dimension using up part of the tolerance; you then work tighter than the drawing asks.
How often is a work origin set?
At least once per setup. For a batch in a vice with a fixed stop, the first piece often suffices, with later checks; on a fixture or zero-point system it is fixed once measured in. Castings or rough parts are sometimes probed piece by piece.