docs/wiki/gcode-reference.md

G-code Reference for CNC Milling

Motion Codes (Modal Group 1)

Modal codes remain active until replaced by another code from the same group.

Code	Function	Parameters
G00	Rapid positioning (max speed, no cutting)	X Y Z
G01	Linear interpolation (cutting feed)	X Y Z F
G02	Circular interpolation, clockwise	X Y Z I J K / R, F
G03	Circular interpolation, counter-clockwise	X Y Z I J K / R, F

Arc Interpolation (G02/G03)

Two formats for specifying arcs:

Center Offset (I, J, K):

• I = X-offset from current position to arc center
• J = Y-offset from current position to arc center
• K = Z-offset (for helical arcs)
• In XY plane (G17): uses I, J
• In XZ plane (G18): uses I, K
• In YZ plane (G19): uses J, K

Radius (R):

• R > 0: arc < 180 degrees
• R < 0: arc > 180 degrees

Example:

G02 X10 Y0 I5 J0 F200   ; CW arc to (10,0), center offset (5,0)
G03 X0 Y10 R10 F200      ; CCW arc to (0,10), radius 10

Plane Selection (Modal Group 2)

Code	Function
G17	XY plane (default for milling)
G18	ZX plane
G19	YZ plane

Distance Mode (Modal Group 3)

Code	Function
G90	Absolute positioning
G91	Incremental positioning

Units (Modal Group 6)

Code	Function
G20	Inch mode
G21	Millimeter mode

Canned Drilling Cycles (Modal Group 1)

Code	Function	Key Params
G80	Cancel canned cycle	--
G81	Simple drilling	X Y Z R F L
G82	Spot drill with dwell	X Y Z R P F L
G83	Deep-hole peck drilling (full retract)	X Y Z R Q F L
G84	Right-hand tapping	X Y Z R F L
G85	Boring, feed out	X Y Z R F L
G86	Boring, spindle stop, rapid out	X Y Z R F L
G73	High-speed peck (chip break, short retract)	X Y Z R Q F L

Parameters:

• R = retract plane (Z height for rapid between holes)
• Q = peck depth increment
• P = dwell time at bottom (milliseconds)
• L = repeat count

Tool Compensation

Code	Function
G40	Cancel cutter radius compensation
G41	Cutter radius compensation left
G42	Cutter radius compensation right
G43	Tool length compensation positive
G49	Cancel tool length compensation

Work Coordinate Systems

Code	Function
G54	Work coordinate system 1 (default)
G55-G59	Work coordinate systems 2-6
G92	Set position (coordinate system offset)

M-Codes (Miscellaneous Functions)

Code	Function
M0	Program pause (operator resume)
M1	Optional stop
M2	Program end
M3	Spindle on, clockwise
M4	Spindle on, counter-clockwise
M5	Spindle stop
M6	Tool change
M7	Mist coolant on
M8	Flood coolant on
M9	Coolant off
M30	Program end and rewind

Feed Rate and Spindle

Letter	Function
F	Feed rate (mm/min or in/min)
S	Spindle speed (RPM)
T	Tool number (e.g., T1, T2)
N	Line number (optional)

Complete G-code Program Example

%
O0001 (POCKET MILLING EXAMPLE)
G21 G90 G17          (mm, absolute, XY plane)
G54                   (work coordinate system 1)

(TOOL 1 - 6MM ENDMILL)
T1 M6                (select tool 1, tool change)
S18000 M3            (spindle 18000 RPM, clockwise)
G43 H1               (tool length compensation)

(RAPID TO START POSITION)
G00 X0 Y0 Z10        (rapid above workpiece)

(POCKET - FIRST PASS)
G00 Z2               (rapid to clearance height)
G01 Z-2 F200         (plunge to depth at feed rate)
G01 X40 F800         (cut along X)
G01 Y30              (cut along Y)
G01 X0               (cut back)
G01 Y0               (cut back to start)

(POCKET - SECOND PASS)
G01 Z-4 F200         (plunge deeper)
G01 X40 F800
G01 Y30
G01 X0
G01 Y0

(RETRACT AND END)
G00 Z50              (rapid retract)
M5                   (spindle off)
M9                   (coolant off)
G28                  (return to reference point)
M30                  (program end)
%

Modal vs Non-Modal

Modal codes stay active: G00, G01, G02, G03, G17-G19, G20/G21, G40-G43, G54-G59, G80-G89, G90/G91

Non-modal codes execute once: G04 (dwell), G28 (return to home), G92 (set position)

Controller Dialects

Feature	LinuxCNC	Grbl	FANUC	Haas
Arc format	I/J/K and R	I/J/K and R	I/J/K and R	I/J/K and R
Canned cycles	Full G73-G89	None	Full G73-G89	Full G73-G89
Tool change	M6	Manual	M6	M6
Subroutines	O-codes	None	M98/M99	M97/M98
Variables	#1-#999	None	#1-#999	#1-#999
Peck drilling	G83	Manual	G83	G83