Mastering G-Code for CNC Machining: Essential Codes You Need to Know

07/15/2025

1. G-Code and Their Functions

G00 — Rapid positioning

G01 — Linear interpolation

G02 — Clockwise circular interpolation

G03 — Counterclockwise circular interpolation

G04 — Dwell (timed pause)

G05 — Circular interpolation through an intermediate point

G06 — Parabolic interpolation

G07 — Z-spline interpolation

G08 — Feed acceleration

G09 — Feed deceleration

G10 — Data setting

G16 — Polar coordinate programming

G17 — XY plane machining

G18 — XZ plane machining

G19 — YZ plane machining

G20 — Inch units (FANUC system)

G21 — Metric units (FANUC system)

G22 — Radius dimension programming

G220 — Used in system operation interface

G23 — Diameter dimension programming

G230 — Used in system operation interface

G24 — Subprogram end

G25 — Jump machining

G26 — Cycle machining

G30 — Scaling cancellation

G31 — Scaling definition

G32 — Constant pitch thread cutting, inch

G33 — Constant pitch thread cutting, metric

G34 — Increasing pitch thread cutting

G35 — Decreasing pitch thread cutting

G40 — Tool compensation/offset cancellation

G41 — Tool compensation left

G42 — Tool compensation right

G43 — Positive tool offset

G44 — Negative tool offset

G45 — Tool offset +/+

G46 — Tool offset +/-

G47 — Tool offset -/-

G48 — Tool offset -/+

G49 — Tool offset 0/+

G50 — Tool offset 0/-

G51 — Tool offset +/0

G52 — Tool offset -/0

G53 — Linear offset cancellation

G54 — Workpiece coordinate system 1

G55 — Workpiece coordinate system 2

G56 — Workpiece coordinate system 3

G57 — Workpiece coordinate system 4

G58 — Workpiece coordinate system 5

G59 — Workpiece coordinate system 6

G60 — Exact path mode (fine)

G61 — Exact path mode (medium)

G62 — Exact path mode (rough)

G63 — Thread tapping

G68 — Tool offset, internal corner

G69 — Tool offset, external corner

G70 — Inch units (Siemens system)

G71 — Metric units (millimeters)

G74 — Return to reference point (machine zero)

G75 — Return to programmed coordinate zero

G76 — Thread cutting composite cycle

G80 — Fixed cycle cancellation

G81 — Outer circle fixed cycle

G331 — Thread fixed cycle

G90 — Absolute dimension

G91 — Incremental dimension

G92 — Preset coordinate

G93 — Inverse time feed rate

G94 — Feed rate per minute

G95 — Feed rate per revolution

G96 — Constant surface speed control

G97 — Cancel constant surface speed control

2. Detailed Explanation of G-Code Functions

Rapid Positioning

Format: G00 X(U)__ Z(W)__

Description:

This command moves the tool rapidly to a specified position in point-to-point control mode. No machining occurs during movement.
All programmed axes move simultaneously at the speed defined by parameters. When one axis reaches its programmed value, it stops, while other axes continue moving.
Coordinates that do not need to move do not require programming.
G00 can be written as G0.

Example:

G00 X75 Z200
G01 U-25 W-100
The tool moves rapidly 25 units along both X and Z axes to point A, then Z moves an additional 75 units rapidly to point B.

Linear Interpolation

Format: G01 X(U)__ Z(W)__ F__(mm/min)

Description:

This command moves the tool to a specified position using linear interpolation. The movement speed is determined by the feed rate specified with the F command.
All coordinates can move simultaneously (linked motion).
G01 can be written as G1.

Example:

G01 X40 Z20 F150
The tool moves with two-axis linkage from point A to point B at a feed rate of 150 mm/min.

Circular Interpolation

Format 1: G02 X(U)__ Z(W)__ I__ K__ F__

Description:

When using G90, X and Z represent the absolute coordinates of the arc’s endpoint relative to the programmed zero point. In G91, they represent incremental values relative to the arc’s starting point. Regardless of G90 or G91, I and K are the incremental coordinates of the arc’s center relative to the starting point. I corresponds to the X direction, and K to the Z direction. The arc center coordinates must not be omitted unless another programming format is used.
The G02 command allows programming of quadrant arcs, full circles, etc. Note: When crossing quadrants, backlash compensation is automatically applied. If the backlash compensation set in the parameters significantly differs from the machine’s actual backlash, visible machining marks may appear on the workpiece.
G02 can be written as G2.

Example: G02 X60 Z50 I40 K0 F120
The tool follows a clockwise arc to X60, Z50 with a center offset of I40 (X direction) and K0 (Z direction) at a feed rate of 120 mm/min.

Format 2: G02 X(U)__ Z(W)__ R(+/-)__ F__

Description:

This format cannot be used for full-circle programming.
R is the radius of the arc on one side of the workpiece. R is signed: “+” indicates an arc angle less than 180 degrees (can be omitted); “-” indicates an arc angle greater than 180 degrees.
Based on the endpoint coordinates, if the distance between the start and endpoint is greater than 2R, the arc is replaced by a straight line.

Example: G02 X60 Z50 R20 F120

Format 3: G02 X(U)_ Z(W)_ CR=(radius) F

Format 4: G02 X(U)_ Z(W)_ D_(diameter) F_

Description:
These formats are essentially the same as Format 2, with CR specifying the radius and D specifying the diameter of the arc.

Counterclockwise Circular Interpolation

Description: The format is identical to the G02 command, except the arc rotates in the opposite (counterclockwise) direction.

Dwell (Timed Pause)

Format: G04_F_ or G04_K_

Description: Machining movement pauses for a specified duration, then resumes. The pause time is defined by the value following F, in seconds, with a range of 0.01 to 300 seconds.

Circular Interpolation via Intermediate Point

Format: G05 X(U)_ Z(W)_ IX_ IZ_ F_

Description: X and Z are the endpoint coordinates, while IX and IZ are the intermediate point coordinates. Other aspects are similar to G02/G03.

Example: G05 X60 Z50 IX50 IZ60 F120

Acceleration/Deceleration

Format: G08

Description: Occupies a single program line. When executed, the feed rate increases by 10%. To increase by 20%, two separate G08 lines are required.

Radius Programming

Format: G22

Description: Occupies a single program line. The system operates in radius mode, and subsequent values in the program are interpreted as radius dimensions.

Diameter Dimension Programming

Format: G23

Description: Occupies a single program line. The system operates in diameter mode, and subsequent values in the program are interpreted as diameter dimensions.

Jump Machining

Format: G25 LXXX

Description: When the program reaches this line, it jumps to the specified program segment (XXX represents the segment number).

Cycle Machining

Format: G26 LXXX QXX

Description: When the program reaches this line, the specified program segment (from LXXX to this line) is treated as a loop, with the number of cycles determined by the value following Q.

Scaling Cancellation

Format: G30

Description: Occupies a single program line. Used in conjunction with G31 to cancel its scaling function.

Ratio Definition

Format: G31 F_

G32: Equal pitch thread machining (imperial)

G33: Equal pitch thread machining (metric)

Format: G32 X(U)_ Z(W)_ F_

Description:

X and Z are endpoint coordinates, F is the thread pitch.
G32 can only machine single-start, single-tool threads.
Changes in X values allow machining of tapered threads.
Spindle speed should not be too high to avoid excessive tool wear.

Constant Pitch Thread Cutting (Metric)

Format: G33 X(U)_ Z(W)_ F_

Description: Same as G32, but for metric threads.

Set Workpiece Coordinates / Set Spindle Speed Limits

Format: G50 S_ Q_

Description:
S specifies the maximum spindle speed, Q specifies the minimum spindle speed.

Set Workpiece Coordinate Systems

Format: G54

Description: G54 corresponds to the first coordinate system, with its origin position set in the machine parameters.

G55: Sets workpiece coordinate system 2
G56: Sets workpiece coordinate system 3
G57: Sets workpiece coordinate system 4
G58: Sets workpiece coordinate system 5
G59: Sets workpiece coordinate system 6

Exact Path Mode

Format: G60

Description:
During machining with multiple consecutive movements, using exact path programming (G60) introduces a buffering process (i.e., deceleration) before proceeding to the next segment.

Continuous Path Mode

Format: G64

Description:
Relative to G60, this mode is primarily used for rough machining, allowing continuous movement without deceleration between segments.

Return to Reference Point (Machine Zero)

Format: G74 X Z

Description:

No other commands can appear in this program segment.
Coordinates following G74 (X, Z) return to zero in sequence.
The machine must have a reference point switch installed before using G74.
Single-axis return to zero is also possible.

Return to Programmed Coordinate Zero

Format: G75 X Z

Return to Programmed Starting Point

Format: G76

Description:
Returns the tool to the position where machining began.

Outer/Inner Circle Fixed Cycle

Format: G81_X(U)__ Z(W)__ R__ I__ K__ F_

Description:

X, Z are the endpoint coordinates; U, W are incremental values relative to the current point.
R is the diameter to be machined at the starting section.
I is the roughing feed, K is the finishing feed. Both I and K are signed values and must have the same sign. The sign convention is: “-” for cutting from the outer surface toward the center axis (outer circle), and “+” for the opposite.
Different combinations of X, Z, and R determine various shapes, such as tapered or non-tapered, positive or negative taper, and left or right cutting.
F specifies the cutting speed (mm/min).
After machining, the tool stops at the endpoint.

Example: G81 X40 Z100 R15 I-3 K-1 F100

Machining Process:

G01 feeds at twice the I value (first cut at I, final cut at I+K for finishing), performing deep cutting.
G01 performs two-axis interpolation to cut to the endpoint section, stopping if machining is complete.
G01 retracts the tool by I to a safe position, simultaneously smoothing the auxiliary cutting surface.
G00 rapidly advances to a position outside the workpiece by I, reserving I for the next cutting step, and repeats from step 1.

Absolute Programming

Format: G90

Description:

When G90 is programmed, all subsequent coordinate values are based on the programmed zero point.
The machine defaults to G90 mode upon power-on.

Example:
N0010 G90 G92 X20 Z90
N0020 G01 X40 Z80 F100
N0030 G03 X60 Z50 I0 K-10
N0040 M02

Incremental Programming

Format: G91

Description:
When G91 is programmed, all subsequent coordinate values are calculated as incremental movements relative to the previous coordinate position. Each new segment uses the previous point as the starting point for programming.

Example:
N0010 G91 G92 X20 Z85
N0020 G01 X20 Z-10 F100
N0030 Z-20
N0040 X20 Z-15
N0050 M02

Set Workpiece Coordinate System

Format: G92 X__ Z__

Description:

G92 changes the displayed coordinate values in the system without moving the axes, effectively setting the coordinate origin.
The effect of G92 is to update the displayed tool tip coordinates to the specified values.
X and Z after G92 can be programmed individually or together.

Feed Rate Per Minute: G94

Description:
This is the default machine state upon power-on, where the feed rate is specified per minute.

Subprogram Call

Format: G20 L_ N_

Description:

L specifies the subprogram name following N, but N itself is not included in the input. The number following N must be between 1 and 99999999.
No other content is allowed in this program segment.

Subprogram End and Return

Format: G24

Description:

G24 indicates the end of a subprogram and returns to the next segment of the calling program.
G24 is used in pair with G20.
No other commands are allowed in the G24 segment.

3. G-code Programming Examples

Example: The following example illustrates the process of passing parameters in the subroutine calling process, please note the application.

Program name: P10

M03 S1000

G20 L200

M02

N200 G92 X50 Z100

G01 X40 F100

Z97

g02 z92 x50 i10 k0 f100

G01 Z-25 F100

G00 X60

Z100

G24

For multiple recalls, use the following format

M03 S1000

N100 G20 L200

N101 G20 L200

N105 G20 L200

M02

N200 G92 X50 Z100

G01 X40 F100

Z97

g02 z92 x50 i10 k0 f100

G01 Z-25 F100

G00 X60

Z100

G24

G331-Threading cycle

Format: G331 X_ Z_I_K_R_p_

Description:

(1) X varies toward the diameter, X=0 is a straight thread

(2) Z is the thread length, absolute or relative programming is possible

(3) I is the length of the thread in the X direction after cutting the tail, ± value

(4) R is the diameter difference between the outer diameter of the thread and the root diameter, positive value

(5) K pitch KMM

(6) p thread cycle processing times, i.e., cut in a few cuts

Tips:

(1) each feed depth of R ÷ p and rounding, the last knife does not feed to lighten the thread surface

(2) The backing off of internal threads is based on the positive and negative directions along X to determine the designation of the I value.

(3) The starting position of the threading cycle is the point of the tool aligned with the outer circle of the thread.

Example:

G4 f2

G0 x30 z0

G331 z-50 x0 i10 k2 r1.5 p5

G0 z0

M05

4. Additional Information and Notes

1. G00 vs. G01

G00: Moves in straight or polyline paths for point positioning only, not for cutting.
G01: Moves in a straight line to the specified target point at the designated feed rate, typically used for cutting operations.

2. G02 vs. G03

G02: Clockwise circular interpolation.
G03: Counterclockwise circular interpolation.

3. G04: Dwell or Pause Command

Used for spindle forward/reverse switching, machining blind holes, stepped holes, or turning grooves.

4. G17, G18, G19: Plane Selection Commands

Specifies the machining plane, typically used for milling machines and machining centers.
G17: X-Y plane (default, can be omitted) or a plane parallel to X-Y.
G18: X-Z plane or a parallel plane; in CNC lathes, only the X-Z plane is used, no specific designation needed.
G19: Y-Z plane or a parallel plane.

5. G27, G28, G29: Reference Point Commands

G27: Returns to the reference point to check and confirm its position.
G28: Automatically returns to the reference point via an intermediate point.
G29: Returns from the reference point, used in conjunction with G28.

6. G40, G41, G42: Radius Compensation