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G21 Metric units
Mach3 Mach4 G-code · Mill
Program values are read in millimeters. It does not change the configured native units of the machine.
Format
G21
Addresses
| Address | What it does |
|---|---|
G21 | No address words |
How it works
Modal, units group.
Example program
G0 G21 G90 G54 G17 G40 G49 G80 (METRIC SAFE START)
T1 M6 (TOOL CHANGE)
S5000 M3 (SPINDLE ON)
G43 H1 Z25.0 (LENGTH OFFSET)
…
T1 M6 (TOOL CHANGE)
S5000 M3 (SPINDLE ON)
G43 H1 Z25.0 (LENGTH OFFSET)
…
The full 5-line example is in the app. Example is in inch. Check offsets and clearances first.
Watch out for
- Program G20 or G21 once at the top, before any motion, and do not switch mid program.
- Mach3 also accepts G70 and G71 for inch and metric. Those are not the Fanuc lathe cycles.
- Units in Motor Tuning and offsets are separate from G20 and G21. Check the DRO units on the screen.
Related codes
G21 on other controls
The same number can mean something different on another control.
| Control | Meaning |
|---|---|
| Fanuc | Metric input |
| Haas NGC | Metric programming check |
| Mazak (EIA) | Metric input |
| Okuma OSP | Metric input confirmation |
| Mitsubishi M70 M80 | Metric input |
| Brother Speedio | Metric input |
| LinuxCNC Tormach | Millimeter units |
| Centroid CNC12 Acorn | Metric units |
| Hurco WinMax (NC) | Metric input (ISNC) |
| Fadal | Check for metric setting |
| Swiss (Citizen Star) | Metric input |
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Open G21 in the app All Mach3 Mach4 G-codes