G-Code Command Reference Table

Q: Can a wrong G-code damage the machine?

Yes. For examples:Using G00 (rapid move) instead of G01 (slow cut) → Tool crashes into the workpiece.Forgetting M05 (spindle stop) → Spinner keeps rotating after the program ends.

Q: How do I use G-code safely?

Test first: Run programs in “dry run” mode (no cutting).Single-block mode: Execute one line at a time to catch errors.Backup settings: Note down machine offsets before editing.Clean workspace: Remove debris that could interfere with motion.

By: HDCMFG
March 10, 2025

G-code (Geometric Code) is the universal programming language used to control CNC (Computer Numerical Control) machines. Developed in the 1950s at MIT, G-code remains the backbone of modern CNC machining, enabling precise control over machining processes like milling, turning, and laser cutting.

Each G-code command starts with a letter (e.g., G, M, or F) followed by numerical values, directing the machine to:

Control movement (G-commands): Determine the tool’s path and speed (e.g., moving to coordinates, linear/arc motion).
Manage functions (M-commands): Handle start/stop actions (e.g., spindle rotation, tool changes, coolant on/off).

While standardized under ISO 6983, variations exist across machine manufacturers (e.g., Fanuc, Haas, Siemens). This table covers 90% of general-purpose G-codes. For advanced functions (5-axis, macros), always consult your machine’s manual for compatibility.

Key Concepts:

Modal Commands: Remain active until replaced (e.g., G01 stays in linear motion mode).
Non-Modal Commands: Execute once (e.g., G28 returns to home position).
Units: G20 (inches) / G21 (millimeters).
Coordinate Systems: G54–G59 (work offsets), G90 (absolute positioning), G91 (incremental positioning).
Sequential Execution: The machine reads code line by line, from top to bottom, No skipping or looping unless using advanced features

G-Code Categories

Category	Example Commands	Primary Function
Motion Control	G00, G01, G02, G03	Tool movement (rapid/linear/arc)
Plane Selection	G17, G18, G19	Select working plane (XY/XZ/YZ)
Units & Measurement	G20 (inches), G21 (mm)	Set measurement system
Coordinate Systems	G54-G59, G92	Define work offsets or temporary coordinates
Tool Compensation	G40, G41, G42, G43	Adjust for tool size/length
Canned Cycles	G81-G89	Automated drilling/tapping routines
Spindle Control	M03, M04, M05	Start/stop spindle rotation
Coolant Control	M08, M09	Turn coolant on/off
Program Control	M30, M02	End program/reset machine
Special Functions	G28, G53	Return to home/machine coordinates

Note: 80% of basic programs use just: G00/G01, G17/G20/G21, M03/M05, and M30.

Common G-Code Command Reference Table

Command	Function	Parameters	Example	Notes
G00	Rapid Positioning (Non-cutting move)	X, Y, Z (target coordinates)	`G00 X10 Y5 Z2`	Avoid collisions; no cutting occurs.
G01	Linear Interpolation (Cutting move)	X, Y, Z, F (feed rate)	`G01 X20 Y15 Z0 F150`	Maintain consistent feed rate for surface finish.
G02	Clockwise Circular Interpolation	X, Y, I, J, K (arc center offsets)	`G02 X30 Y30 I5 J0`	I/J/K define arc center relative to start point.
G03	Counter-Clockwise Circular Interpolation	Same as G02	`G03 X40 Y20 I0 J-5`	Used for arcs and circles.
G17	XY Plane Selection	None	`G17`	Default plane for most milling operations.
G18	XZ Plane Selection	None	`G18`	Used for lathe operations.
G19	YZ Plane Selection	None	`G19`	Rarely used in standard milling.
G20	Inch Units	None	`G20`	Sets all values to inches.
G21	Metric Units	None	`G21`	Sets all values to millimeters.
G28	Return to Home Position	X, Y, Z (optional via intermediate)	`G28 X0 Y0 Z0`	Machine moves to reference point.
G40	Cancel Cutter Compensation	None	`G40`	Disables tool radius offset.
G41	Left Cutter Compensation	D (tool radius offset number)	`G41 D1`	Compensates for tool radius to the left of the path.
G42	Right Cutter Compensation	D (tool radius offset number)	`G42 D2`	Compensates for tool radius to the right of the path.
G43	Tool Length Compensation	H (tool height offset number)	`G43 H3`	Adjusts for tool length; critical for multi-tool setups.
G54	Work Coordinate System 1	None	`G54`	Selects pre-defined work offset (G54–G59).
G80	Cancel Motion Modes	None	`G80`	Cancels cycles (e.g., drilling, tapping).
G90	Absolute Positioning	None	`G90`	All coordinates are relative to origin.
G91	Incremental Positioning	None	`G91`	Coordinates are relative to current position.
M03	Spindle Start (Clockwise)	S (spindle speed)	`M03 S2000`	Spindle rotates clockwise at 2000 RPM.
M04	Spindle Start (Counter-Clockwise)	S (spindle speed)	`M04 S1500`	Used for reverse cutting operations.
M05	Spindle Stop	None	`M05`	Stops spindle after operation.
M06	Tool Change	T (tool number)	`M06 T5`	Automatic tool change (requires ATC).
M08	Coolant On	None	`M08`	Activates flood coolant.
M09	Coolant Off	None	`M09`	Turns off coolant.
M30	Program End & Reset	None	`M30`	Ends program and resets machine.
F	Feed Rate	Feed value (units/min or units/rev)	`F200`	Set in G94 (units/min) or G95 (units/rev).
S	Spindle Speed	RPM value	`S3000`	Speed depends on material and tool type.
T	Tool Selection	Tool number	`T4`	Prepares tool for M06 command.

FAQ

Do I need to memorize all G-codes?

No. Modern CAM software generates most code automatically. Focus on understanding common commands like G00, G01, M03, and M30.

Are G-codes the same for all machines?

Basics are universal, but advanced features vary by brand. For example:

Haas: G187 (high-speed mode)
Fanuc: G05.1 (smoothing)

Always check your machine’s manual for specifics.

Can a wrong G-code damage the machine?

Yes. For examples:

Using G00 (rapid move) instead of G01 (slow cut) → Tool crashes into the workpiece.

Forgetting M05 (spindle stop) → Spinner keeps rotating after the program ends.

How do I use G-code safely?

Test first: Run programs in “dry run” mode (no cutting).
Single-block mode: Execute one line at a time to catch errors.
Backup settings: Note down machine offsets before editing.
Clean workspace: Remove debris that could interfere with motion.

Can I edit G-code manually?

Yes, but only tweak values you fully understand and never modify tool paths without CAM software – small errors can cause crashes.

What software creates G-code?

CAM programs: Fusion 360, Mastercam, SolidWorks CAM (paid), FreeCAD, Easel (web-based).

Note: Avoid writing code from scratch unless you’re experienced.

G-Code Command Reference Table

G-Code Categories

Common G-Code Command Reference Table

FAQ

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