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

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

G-Code vs M-Code in CNC Programming

The difference between G-Code and M-Code is fundamental to CNC programming:

7. Common CNC M-Code Errors and Fixes

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