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For milling machines, the direction of machine axes is decided by both the type of machine tool and the
layout of each component. The basic coordinate axes of milling machines are X-axis, Y-axis, and Z-axis:
——Z-axis is coincidental with spindle axis and the direction of the cutter moving away from workpiece is
its positive direction (+Z).
——X-axis is perpendicular to Z-axis and parallel to the clamped surface of workpiece. For the single
column vertical milling machine, if the user faces the spindle and looks in the column direction, right
moving direction is its positive direction (+ X).
——X-axis, Y-axis and Z-axis constitute a coordinate system adhering to the right-hand rule.
3.2.1.
Machine Coordinate System
Machine coordinate system is a set of fixed right-hand coordinate system. Its coordinate origin is always
fixed with respect to a certain position on the machine tool. Therefore, at any time, a certain point in
space can be exclusively fixed by the machine coordinate system.
The machine coordinate system requires the machine available of the homing function, or this concept
will only appear in the software.
3.2.2.
Workpiece Coordinate System
As a set of right-hand coordinate system for the programmer, workpiece coordinate system is used in
programming. To establish it, the programmer can select a given point on the workpiece as the origin
(also called program origin). The origin of workpiece coordinate system (namely the workpiece origin) is
fixed with respect to a certain point on the workpiece, while variable with respect to the machine origin.
The origin of workpiece coordinate system should be selected to facilitate simple programming, easy
dimension conversion and small machining errors.
Workpiece offset corresponds to WCS G54, G55, G56, G57, G58 and G59. After the system is started,
the default WCS is G54, and the relation between workpiece offset and machine coordinate system is as
shown in Fig. 3-3.
G 5 4 (X )
G
5
4
(Y
)
M a c h in e
O r ig in
W o r k p ie c e
O r ig in
L im it o f A x ia l M o t io n
W o r k p ie c e
Fig. 3-3 The relation between workpiece offset and machine coordinate system
