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G91 Incremental dimensions
Siemens 840D 828D G-code · Mill and lathe
End points are distances from the current position. Handy for repeated patterns and subprograms. Single values can be made absolute with AC().
Format
G91
How it works
Modal, G group 14 (absolute or incremental).
Example program
G90 G0 X0 Y0 ; ABSOLUTE START
G91 G1 X20 F300 ; MOVE 20 IN X
Y10 ; MOVE 10 IN Y
G90 ; BACK TO ABSOLUTE
G91 G1 X20 F300 ; MOVE 20 IN X
Y10 ; MOVE 10 IN Y
G90 ; BACK TO ABSOLUTE
Example is in inch. Check offsets and clearances first.
Watch out for
- Go back to G90 after an incremental section. A forgotten G91 sends every later move off by the full value.
- On a lathe with DIAMON, incremental X is also a diameter value. DIAM90 makes incremental X a radius value.
Related codes
G91 on other controls
The same number can mean something different on another control.
| Control | Meaning |
|---|---|
| Fanuc | Incremental programming |
| Haas NGC | Incremental positioning |
| Mazak (EIA) | Incremental programming |
| Okuma OSP | Incremental programming |
| Mitsubishi M70 M80 | Incremental programming |
| Brother Speedio | Incremental programming |
| Heidenhain TNC (ISO) | Incremental dimensions |
| Fagor 8055 8065 | Incremental programming |
| LinuxCNC Tormach | Incremental distance mode |
| Mach3 Mach4 | Incremental mode |
| Centroid CNC12 Acorn | Incremental positioning |
| Hurco WinMax (NC) | Incremental mode |
| Fadal | Incremental positioning |
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