What Is M-Code in CNC? Full Meaning, Applications, and M-Code List
What Is M-Code in CNC ? Full Meaning, Applications, and M-Code List
In CNC machining, M-Code plays a vital role in controlling the machine’s auxiliary functions—everything that is not directly related to cutting paths or tool movements. While G-Codes define “how the machine moves”, M-Codes define “what the machine does”. For machinists, understanding M-Codes is essential for writing efficient and safe CNC programs. In this guide, we’ll explain the meaning of M-Code, its applications, what it can do in CNC, and include a complete Fanuc M-Code list, as well as common troubleshooting tips.
1. What Is M-Code?
M-Code stands for “Machine Code.” It is a set of instructions in CNC programming that controls auxiliary functions such as spindle on/off, coolant control, tool changes, and program stops. While G-Codes (Geometry Codes) manage tool motion, M-Codes handle machine-level commands that make those movements possible. Together, they form the foundation of CNC automation.
Examples include:
M03 – Spindle on (clockwise rotation)
M05 – Spindle stop
M08 – Coolant on
M09 – Coolant off
M30 – End of program and rewind
2. The Meaning of M-Code
Every M-Code carries a specific meaning that triggers an action in the CNC controller. Unlike G-Codes, which often have universal meanings across machines, M-Codes can vary slightly between machine brands (Fanuc, Haas, Siemens, etc.).
3. Applications of M-Code in CNC Machining
Function Type | Example M-Code | Description |
Spindle Control | M03 / M04 / M05 | Turn spindle on (CW/CCW) or off |
Coolant Control | M07 / M08 / M09 | Activate mist, flood, or turn off coolant |
Tool Control | M06 | Automatic tool change |
Program Control | M00 / M01 / M30 | Stop, optional stop, end of program |
Chuck / Tailstock | M10 / M11 / M21 / M22 | Open/close chuck, extend/retract tailstock |
Safety / Door | M40 / M41 | Gear range, safety locks, etc. |
4. What Can M-Code Do?
M-Codes are the “hands and switches” of a CNC machine. They start and stop the spindle, control coolant and air blast, execute tool changes, manage machine doors and clamps, and end or pause the machining program.
5. M-Code List for Fanuc Control – Full Reference
M-Code | Function |
M00 | Program Stop |
M01 | Optional Stop |
M02 | End of Program |
M03 | Spindle On (CW) |
M04 | Spindle On (CCW) |
M05 | Spindle Stop |
M06 | Tool Change |
M08 | Coolant On |
M09 | Coolant Off |
M10 / M11 | Chuck Clamp / Unclamp |
M19 | Spindle Orientation |
M30 | End of Program and Rewind |
M41 / M42 | Gear Range (Low / High) |
M60 | Pallet Change (if available) |
6. G-Code vs M-Code in CNC Programming
The difference between G-Code and M-Code is fundamental to CNC programming:
Aspect | G-Code | M-Code |
Function | Controls motion (geometry) | Controls machine operations |
Example | G01 = Linear cutting | M03 = Spindle on |
Duration | Modal (remains active) | Non-modal (one-time action) |
Focus | Path and feed control | Auxiliary functions |
7. Common CNC M-Code Errors and Fixes
Problem | Possible Cause | Fix |
Alarm: Invalid M-Code | Code not recognized by controller | Check if the M-Code is supported on your machine |
Tool Change Error (M06) | Wrong tool number or offset | Verify tool offset table and magazine position |
Coolant Not Activating (M08) | Coolant tank empty or disabled | Check coolant system and parameters |
Program Not Ending Properly (M30) | Missing M02/M30 command | Always end with M30 or M02 to reset machine |
Conclusion
Understanding M-Codes in CNC machining is crucial for writing safe, efficient, and automated programs. M-Codes enable the control of all auxiliary machine functions while working with G-Codes to complete machining operations.