Explore the ultimate G-Code and M-Code reference guide—covering every essential CNC command, real-world examples, syntax breakdowns, and tips for professional CNC programming and automation.

Complete G-Code and M-Code Reference for CNC Programmers and Machinists

Whether you are a beginner just learning CNC or a seasoned machinist, mastering G-Code and M-Code is essential. These command languages drive everything from basic movements to complex machining operations. This ultimate reference guide provides an in-depth, easy-to-navigate directory of standard and advanced G & M codes used in CNC milling, turning, and automation.

📘 Table of Contents

• 1. What Are G-Codes and M-Codes?
• 2. How CNC Machines Interpret Codes
• 3. Standard G-Code Commands List
• 4. Standard M-Code Commands List
• 5. Advanced G-Code Applications
• 6. G-Code Syntax and Programming Format
• 7. Differences Between Milling and Lathe G-Codes
• 8. Error Troubleshooting with G-Code
• 9. Online Simulators and Testing Tools
• 10. Printable G/M Code Cheat Sheet

1. What Are G-Codes and M-Codes?

G-Code (Geometric Code) controls movement and position (e.g., linear motion, arc paths). M-Code (Miscellaneous Code) controls machine-specific functions like spindle on/off, coolant, and tool changes.

2. How CNC Machines Interpret Codes

CNC controllers interpret the codes line-by-line in a program file (commonly .nc, .tap, or .gcode formats). Each line is typically one instruction, called a block.

3. Standard G-Code Commands List

G-Code	Description
G00	Rapid positioning
G01	Linear interpolation (cutting motion)
G02	Circular interpolation clockwise
G03	Circular interpolation counterclockwise
G17	Select XY plane
G20	Set units to inches
G21	Set units to millimeters
G28	Return to machine home
G40	Cancel cutter compensation
G90	Absolute positioning
G91	Incremental positioning
G94	Feedrate per minute

4. Standard M-Code Commands List

M-Code	Description
M00	Program stop
M01	Optional stop
M02	End of program
M03	Spindle on clockwise
M04	Spindle on counterclockwise
M05	Spindle stop
M06	Tool change
M08	Coolant on
M09	Coolant off
M30	End of program + rewind

5. Advanced G-Code Applications

• Parametric programming with variables (e.g., #100)
• Macros for loops and conditional logic
• Using subprograms with M98 and M99
• Tool radius compensation (G41, G42)
• High-speed roughing routines

6. G-Code Syntax and Programming Format

Each line follows a standard format: N10 G01 X1.0 Y1.0 F100

• N10 = Line number (optional)
• G01 = Motion command
• X1.0 Y1.0 = Position coordinates
• F100 = Feedrate

7. Differences Between Milling and Lathe G-Codes

While many codes are shared, lathe machines use additional turning codes (e.g., G96 for constant surface speed). Some machines use manufacturer-specific extensions or proprietary G/M codes.

8. Error Troubleshooting with G-Code

• ⚠️ Alarm 1: Limit switch triggered
• ⚠️ Alarm 20: Unsupported command
• ✅ Tip: Use a G-code viewer or simulator to verify code before machining

9. Online Simulators and Testing Tools

Try tools like:

• NCViewer – Free G-code visualizer
• CNCjs – Web-based G-code sender with preview
• CAMotics – 3D toolpath simulator

10. Printable G/M Code Cheat Sheet

We’ve created a compact cheat sheet of G-Code and M-Code commands for quick reference in the workshop. Download and print it to keep at your CNC station.

🔚 Conclusion

G-Code and M-Code remain the universal languages of CNC machines. Learning them unlocks full control over motion, tooling, safety, and automation. Whether you’re editing CAM output or writing code by hand, this guide will serve as your foundational reference for professional CNC programming.

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