Even if your CAM generates the toolpath, knowing G-code lets you spot bad programming, recover from interrupted cycles, and make small edits at the machine.
Essential G-codes
| Code | Function |
|---|---|
| G00 | Rapid traverse (max speed, NOT cutting) |
| G01 | Linear feed (cutting at programmed feed rate) |
| G02 / G03 | Circular interpolation CW / CCW |
| G17 / G18 / G19 | Plane select XY / XZ / YZ |
| G20 / G21 | Inch / Metric |
| G40 / G41 / G42 | Cutter compensation off / left / right |
| G43 / G49 | Tool length offset on / off |
| G54-G59 | Work coordinate systems (WCS) |
| G80 / G81 / G83 | Cancel cycle / drill / peck-drill |
| G90 / G91 | Absolute / Incremental positioning |
| G94 / G95 | Feed per minute / per revolution |
Essential M-codes
- M00 — Program stop (pause)
- M01 — Optional stop (only if button pressed)
- M03 / M04 / M05 — Spindle CW / CCW / off
- M06 — Tool change
- M08 / M09 — Coolant on / off
- M30 — Program end + reset
Reading a Sample Block
N50 G01 X25.4 Y10.0 Z-2.5 F300
- N50 — Block (line) number 50
- G01 — Linear feed move
- X25.4 Y10.0 Z-2.5 — Move to these coordinates
- F300 — Feed rate 300 mm/min
Common Tool Change Block
T05 M06 ; G43 H05 Z50.0 ; M03 S2500 ; M08
Translation: Change to tool 5; activate length offset stored in H05; move Z to safe height; spindle on at 2500 RPM clockwise; coolant on.
Where to Look in Your Program
- Top: tool number, WCS, units (G20/G21)
- Bottom: M30 (or M02) to confirm proper end
- Look for any feed rate (F) suspiciously high or low
- Verify Z-axis safe positions before tool changes
For tooling that fits your G-code, browse our insert catalog.
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