CNC Machining

G code

G Code is used to control the path of the machine tool. There isn’t one universal list of all CNC G- and M-codes: G-codes vary by controller (Fanuc, Haas, Siemens, Mitsubishi, LinuxCNC, etc.), and M-codes are especially machine-builder-specific. Below is a comprehensive Fanuc/Haas-style reference covering the commonly encountered codes. Some codes have different meanings depending on the controller or machine.

CNC G Codes

G Code	Function	Description
G00	Rapid positioning	Moves the tool rapidly to a specified position
G01	Linear interpolation	Cuts in a straight line at the programmed feed rate
G02	Circular interpolation CW	Cuts an arc clockwise
G03	Circular interpolation CCW	Cuts an arc counterclockwise
G04	Dwell	Pauses for a specified amount of time
G05	High-speed/high-precision mode	Controller-dependent; advanced contouring
G09	Exact stop	Temporarily forces an exact stop at the end of a block
G10	Programmable data input	Allows offsets/settings to be programmed
G11	Cancel programmable data input	Cancels G10 mode
G12	Circular pocket milling CW	Controller-dependent
G13	Circular pocket milling CCW	Controller-dependent
G15	Polar coordinates cancel	Cancels polar coordinate mode
G16	Polar coordinate mode	Enables polar coordinate programming
G17	XY plane selection	Selects XY plane for circular interpolation
G18	XZ plane selection	Selects XZ plane
G19	YZ plane selection	Selects YZ plane
G20	Inch programming	Coordinates interpreted in inches
G21	Metric programming	Coordinates interpreted in millimeters
G28	Return to machine zero	Returns machine to reference/home position
G30	Return to 2nd/other reference point	Returns to an alternate machine reference position
G31	Skip/probe function	Used for probing or skip movements
G32	Thread cutting	Synchronizes feed with spindle for threading
G33	Thread cutting	Controller-dependent threading cycle
G40	Cutter compensation cancel	Cancels tool-radius compensation
G41	Cutter compensation left	Applies cutter compensation to the left of the programmed path
G42	Cutter compensation right	Applies cutter compensation to the right
G43	Tool length compensation +	Applies positive tool-length offset
G44	Tool length compensation −	Applies negative tool-length offset; controller-dependent
G49	Tool length compensation cancel	Cancels G43/G44
G50	Scaling/spindle speed limit	Meaning varies by controller; commonly cancels scaling or sets maximum spindle speed
G51	Scaling	Enables programmable scaling
G52	Local coordinate system	Establishes a temporary local coordinate shift
G53	Machine coordinate system	Executes movement using machine coordinates
G54	Work coordinate system 1	Selects work offset #1
G55	Work coordinate system 2	Selects work offset #2
G56	Work coordinate system 3	Selects work offset #3
G57	Work coordinate system 4	Selects work offset #4
G58	Work coordinate system 5	Selects work offset #5
G59	Work coordinate system 6	Selects work offset #6
G54.1 P1–P48	Extended work offsets	Additional work coordinate systems; availability varies
G61	Exact stop mode	Commands exact stopping/precision behavior
G61.1	High-precision contour control	Controller-dependent
G64	Cutting/continuous mode	Cancels exact-stop behavior on controllers that support it
G65	Macro call	Calls a custom macro/subprogram with arguments
G66	Modal macro call	Calls a macro repeatedly in subsequent blocks
G67	Cancel modal macro	Cancels G66
G68	Coordinate rotation	Rotates the coordinate system
G69	Cancel coordinate rotation	Cancels G68
G70	Finishing cycle	Finishing cycle for turning
G71	Rough turning cycle	Automatic roughing cycle
G72	Facing roughing cycle	Rough-facing cycle
G73	Pattern/peck drilling cycle	Meaning varies between mill and lathe
G74	Left-hand tapping / peck drilling	Function depends on machine
G75	Grooving/peck cycle	Commonly used for repetitive grooving on lathes
G76	Threading cycle	Automatic multi-pass threading cycle
G80	Canned cycle cancel	Cancels active drilling/boring cycle
G81	Drilling cycle	Basic drilling canned cycle
G82	Spot drilling/counterboring	Drilling cycle with dwell
G83	Peck drilling	Deep-hole drilling with retracts
G84	Tapping cycle	Right-hand tapping
G85	Boring cycle	Boring with feed in and feed out
G86	Boring cycle	Bores then stops spindle/retracts
G87	Back boring cycle	Boring from the opposite side
G88	Boring cycle	Controller-dependent
G89	Boring cycle with dwell	Boring cycle with dwell
G90	Absolute programming	Coordinates measured from the active work zero
G91	Incremental programming	Coordinates measured from the current position
G92	Coordinate/spindle setting	Meaning varies; often coordinate-system or spindle-speed limiting function
G94	Feed per minute	Feed specified in distance per minute
G95	Feed per revolution	Feed specified per spindle revolution
G96	Constant surface speed	Automatically varies spindle RPM to maintain surface speed
G97	Constant RPM	Cancels constant surface speed
G98	Return to initial point	Canned cycle returns to initial Z position
G99	Return to R point	Canned cycle returns to the R-plane

Common Turning-Specific G Codes

G Code	Function	Description
G20	Inch mode	Programming in inches
G21	Metric mode	Programming in millimeters
G32	Thread cutting	Single-point threading
G50	Spindle speed limit	Sets maximum RPM during CSS
G70	Finishing cycle	Finishes a previously defined roughing profile
G71	Rough turning	Removes material from OD/ID profile
G72	Rough facing	Removes material from a facing profile
G73	Pattern repeating cycle	Repeats a profile with controlled depth
G74	Peck drilling	Common lathe drilling/pecking cycle
G75	Grooving cycle	Repetitive grooving/pecking
G76	Multiple-pass threading	Automatic threading cycle
G96	Constant surface speed	Maintains programmed surface speed
G97	Constant spindle speed	RPM remains fixed
G98	Feed per minute	Feed specified in distance/minute
G99	Feed per revolution	Feed specified in distance/revolution

Common Milling-Specific G Codes

G Code	Function	Description
G00	Rapid	Rapid tool movement
G01	Linear interpolation	Straight-line cutting
G02	CW arc	Clockwise circular movement
G03	CCW arc	Counterclockwise circular movement
G17	XY plane	Standard milling plane
G18	XZ plane	XZ circular interpolation
G19	YZ plane	YZ circular interpolation
G40	Cancel cutter compensation	Turns off G41/G42
G41	Cutter comp left	Tool compensation left of path
G42	Cutter comp right	Tool compensation right of path
G43	Tool length compensation	Applies H offset
G49	Cancel tool length compensation	Cancels G43
G54–G59	Work offsets	Selects work coordinate system
G80	Cancel canned cycle	Turns off drilling cycle
G81	Drill	Standard drilling
G82	Spot drill	Drill with dwell
G83	Peck drill	Deep-hole drilling
G84	Tap	Right-hand tapping
G85	Bore	Feed in/feed out boring
G86	Bore	Spindle stop before retract
G87	Back bore	Back boring
G88	Bore	Controller-dependent boring cycle
G89	Bore with dwell	Boring with dwell
G90	Absolute	Position from work zero
G91	Incremental	Position from current location
G94	Feed/minute	F value represents distance/minute
G95	Feed/revolution	F value represents distance/revolution
G98	Initial-point return	Canned cycle returns to starting Z
G99	R-plane return	Canned cycle returns to R-plane

M Code

CNC M-Codes

M-codes control machine functions rather than tool motion. Unlike G-codes, M-codes are heavily dependent on the machine builder and controller. The following are common Fanuc/Haas-style M-codes.

M Code	Function	Description
M00	Program stop	Stops program completely; operator must restart
M01	Optional stop	Stops only when optional-stop switch is enabled
M02	End of program	Ends program
M03	Spindle CW	Starts spindle clockwise
M04	Spindle CCW	Starts spindle counterclockwise
M05	Spindle stop	Stops spindle
M06	Tool change	Executes programmed tool change
M07	Mist coolant	Turns mist coolant on; machine-dependent
M08	Flood coolant	Turns flood coolant on
M09	Coolant off	Turns coolant off
M10	Chuck/clamp	Machine-dependent; commonly clamps
M11	Chuck/unclamp	Machine-dependent; commonly unclamps
M13	Spindle CW + coolant	Starts spindle CW and coolant
M14	Spindle CCW + coolant	Starts spindle CCW and coolant
M19	Spindle orientation	Orients spindle to a specified position
M21	Tailstock forward	Lathe-specific
M22	Tailstock reverse	Lathe-specific
M23	Chamfer/departure	Controller/machine-dependent
M24	Threading/chamfer function	Machine-dependent
M30	End and reset	Ends program and resets to beginning
M31	Chip conveyor forward	Starts chip conveyor; machine-dependent
M32	Chip conveyor reverse	Machine-dependent
M33	Chip conveyor stop	Machine-dependent
M41	Low gear	Selects low spindle gear
M42	High gear	Selects high spindle gear
M48	Override enabled	Enables feed/spindle overrides; controller-dependent
M49	Override disabled	Disables feed/spindle overrides
M51	Auxiliary output ON	Machine-builder dependent
M52	Auxiliary output OFF	Machine-builder dependent
M60	Pallet change	Executes pallet change on supported machines
M61	Fixture/clamp function	Machine-dependent
M62	Output ON	Turns programmable output on
M63	Output ON	Alternative programmable output
M64	Output OFF	Turns programmable output off
M65	Output OFF	Alternative programmable output
M66	Wait for input	Waits for an input signal; controller-dependent
M67	Analog output	Machine/controller-dependent
M68	Hydraulic chuck clamp	Common lathe function; machine-dependent
M69	Hydraulic chuck unclamp	Common lathe function; machine-dependent
M70	Mirror image	Controller-dependent
M71	Mirror image	Controller-dependent
M72	Mirror image cancel	Controller-dependent
M73	Mirror image cancel	Controller-dependent
M80	Auto door open	Machine-dependent
M81	Auto door close	Machine-dependent
M88	Through-spindle coolant ON	Turns TSC on
M89	Through-spindle coolant OFF	Turns TSC off
M97	Local subprogram call	Calls a local subprogram; common on Haas
M98	Subprogram call	Calls an external/local subprogram
M99	Subprogram return	Returns from subprogram; can also create a loop
M101+	Auxiliary functions	Machine-builder/controller dependent

Important: M-codes vary significantly

For example, M10 and M11 can mean chuck clamp/unclamp on one machine but something completely different on another. Likewise, M08 is commonly flood coolant, but additional coolant functions such as through-spindle coolant can use different codes depending on the manufacturer.

The same applies to G-codes. For example, G73 can represent a drilling cycle on a mill but a completely different cycle on a lathe.

The most important codes to memorize

If you’re learning CNC programming, I’d start with these:

Movement

G00 — Rapid
G01 — Linear cut
G02 — CW arc
G03 — CCW arc

Coordinates

G20 — Inch
G21 — Metric
G90 — Absolute
G91 — Incremental
G54–G59 — Work offsets

Tool compensation

G40 — Cancel cutter compensation
G41 — Cutter compensation left
G42 — Cutter compensation right
G43 — Tool length compensation
G49 — Cancel tool length compensation

Drilling

G80 — Cancel canned cycle
G81 — Drill
G82 — Drill with dwell
G83 — Peck drill
G84 — Tap

Spindle/cutting

G94 — Feed per minute
G95 — Feed per revolution
G96 — Constant surface speed
G97 — Constant RPM

Machine functions

M00 — Program stop
M01 — Optional stop
M03 — Spindle CW
M04 — Spindle CCW
M05 — Spindle stop
M06 — Tool change
M08 — Coolant on
M09 — Coolant off
M30 — End/reset
M98 — Subprogram call
M99 — Subprogram return

Note: This is a practical reference, not a universal controller manual. For actual machining, the specific control’s programming manual (e.g., Haas NGC, Fanuc 0i/31i, Siemens SINUMERIK, Mitsubishi, LinuxCNC) should take precedence because unsupported or differently defined codes can cause unexpected machine behavior.