FANUC G68 followed by a single-axis command: why the same absolute command can reach different positions
The 0i-D machining-center manual explains how 11600#5 AX1 handles omitted axes after rotation. An original 90-degree example compares endpoints for a Y-only command and an explicit XY command.
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Even with G90 active, absolute coordinates after rotation may be ambiguous to the programmer: when only Y is specified, which coordinate system supplies the omitted X value? On 0i-D / 0i Mate-D machining centers, the words “absolute programming” alone do not answer that question.
AX1 determines how the omitted axis enters the calculation
B-64304EN-2/01, §6.10, printed pages 226–227 (public mirror of the original manual) defines 11600#5 AX1: with 0, the target is determined in the pre-rotation coordinate system and then rotated; with 1, the position is first converted into the rotated coordinate system, then the specified axis coordinate is applied. If both axes in the plane are specified, this bit does not change the endpoint. This explains the existing configuration, not a recommendation to change parameters to accommodate a program.
Calculate both interpretations
This original example is limited to the G17 XY plane, G90 absolute coordinates, rotation center (0,0), and 90° counterclockwise rotation, without scaling, mirroring or tool compensation. Before rotation is enabled, the actual position in the original XY frame is (20,10) mm. The next request specifies only Y=30 mm. The 90° transformation is (x,y)→(−y,x).
| Existing configuration | Handling of the omitted axis | Endpoint in the original XY frame |
|---|---|---|
| AX1=0 | First form (20,30), then rotate 90° | (−30,20) mm |
| AX1=1 | Convert the current position to (10,−20) in the rotated frame, then set Y′ to 30 | (−30,10) mm |
The target in the second row is (10,30) in the rotated frame. Transforming it back to the original XY frame gives (−30,10). The same single-axis request produces a 10 mm endpoint difference because of how the omitted coordinate is interpreted, not necessarily because of servo positioning error.
Resolving this ambiguity during program transfer
In the model above, explicitly specifying the target in rotation coordinates as X=20, Y=30 gives (−30,20) in the original XY frame under either configuration. When transferring a program from another machine, first locate the initial absolute move after rotation that omits an axis in the plane. Recalculate it using the position before rotation, instead of comparing only the G68 angle.
This does not mean that simply adding an X word makes the program production-ready. First establish whether that X value expresses the design intent, and check entry and exit paths in a validation environment matching the target machine configuration.
Canceling rotation also has mode restrictions
Pages 225–226 of the same edition prohibit changing G17 / G18 / G19 during rotation and require the first move after G69 cancellation to use absolute values. This example concerns planar rotation; it does not define coordinate rules for a tilted working plane or TCP. Availability depends on machine configuration. Inclusion in the OPTION section does not mean that every basic programming function is separately chargeable.