CNC machines G-Code List

G-code is the universal programming language for CNC machines. It’s used to control movements, speeds, tool changes, and other operations. While G-code can seem overwhelming at first, having a complete guide makes it much easier to understand and reference. Let’s cover the most important G-code commands, what they do, and how they’re used.

What is G-Code?

G-code (Geometric Code) is a series of instructions that tell your CNC machine how to perform specific actions. Each command begins with a letter, such as G, M, or F, followed by numbers that define parameters. G-code enables precise control of:

• Tool movement (X, Y, Z axes)
• Cutting paths and patterns
• Tool changes and offsets
• Spindle and feed rates

Let’s break down the essential G-code commands you’ll use in CNC machining.

Common G-Code Commands

G00 – Rapid Positioning

Moves the tool quickly to a specified position without cutting.

Example:

G00 X10 Y20 Z5

Moves the tool to X=10, Y=20, Z=5 as fast as possible.

G01 – Linear Interpolation

Moves the tool in a straight line at a controlled feed rate for cutting.

Example:

G01 X50 Y50 F200

Cuts a straight line to X=50, Y=50 at 200 units per minute.

G02 – Circular Interpolation (Clockwise)

Cuts an arc or circle in a clockwise direction.

Example:

G02 X20 Y20 I10 J0

Cuts a clockwise arc to X=20, Y=20 with a center offset I=10, J=0.

G03 – Circular Interpolation (Counterclockwise)

Cuts an arc or circle in a counterclockwise direction.

Example:

G03 X20 Y20 I10 J0

Cuts a counterclockwise arc to X=20, Y=20 with a center offset I=10, J=0.

G20/G21 – Units

Sets the units for measurements.

• G20: Inches
• G21: Millimeters

Example:

G21

Sets units to millimeters.

G28 – Return to Home Position

Moves the tool to the machine’s predefined home position.

Example:

G28

Sends the tool to its home position.

G90 – Absolute Positioning

Coordinates are relative to the origin (0,0,0).

Example:

G90

Sets absolute positioning mode.

G91 – Incremental Positioning

Coordinates are relative to the tool’s current position.

Example:

G91

Sets incremental positioning mode.

G17/G18/G19 – Plane Selection

Specifies the cutting plane.

• G17: XY plane
• G18: ZX plane
• G19: YZ plane

Example:

G17

Cuts in the XY plane.

G40/G41/G42 – Tool Compensation

Adjusts for the tool’s radius during cutting.

• G40: Cancel compensation
• G41: Left compensation
• G42: Right compensation

Example:

G41 D1

Activates left compensation using tool diameter 1.

G43/G49 – Tool Length Compensation

Accounts for the tool’s length to ensure proper cutting depth.

• G43: Apply compensation
• G49: Cancel compensation

Example:

G43 H1

Applies tool length offset for tool 1.

G54-G59 – Work Offsets

Sets alternative coordinate systems for different workpieces.

Example:

G54

Activates work offset 1.

Common M-Code Commands

M03 – Spindle On (Clockwise)

Starts the spindle in a clockwise direction.

Example:

M03 S1200

Starts the spindle at 1200 RPM.

M05 – Spindle Off

Stops the spindle.

Example:

M05

Turns off the spindle.

M06 – Tool Change

Initiates a tool change.

Example:

M06 T2

Changes to tool 2.

M30 – End Program

Marks the end of the program and resets the machine.

Example:

M30

Ends the program.

360 Key Takeaways

• G-code commands control every aspect of CNC machining, from movement to tool changes.
• Common commands like G00, G01, and M03 are essential for basic operations.
• Tool compensation (G41, G42) and length adjustments (G43) ensure precise cuts.
• M-codes handle auxiliary machine functions like spindle control and program termination.
• Familiarity with these commands makes it easier to write, debug, and modify G-code programs.

Conclusion

This guide to G-code provides a solid foundation for CNC programming. Whether you’re writing code manually or modifying code generated by CAM software, understanding these commands is crucial. Keep this guide handy as a reference, and with practice, you’ll master G-code programming in no time.