G Code for Milling Slot: Syntax, Example & Tips

To mill a slot using G-code, use G1 for linear cutting moves combined with X, Y, and Z coordinates to define the slot path and depth. Typically, you start with a rapid move (G0) to the slot start, then use G1 to cut along the slot length and width at the desired feed rate.

Syntax

The basic G-code commands for milling a slot include:

• G0: Rapid move to position without cutting.
• G1: Linear move with cutting at a set feed rate.
• X, Y: Coordinates for horizontal movement.
• Z: Coordinate for vertical movement (depth).
• F: Feed rate (speed of cutting).

Use G0 to position the tool above the slot start, then G1 to plunge into the material and move along the slot path.

gcode

G0 X10 Y10 Z5 ; Rapid move above slot start
G1 Z-2 F100 ; Plunge into material 2mm deep at feed rate 100
G1 X50 Y10 F200 ; Cut slot length
G1 X50 Y20 ; Cut slot width
G1 X10 Y20 ; Cut back along width
G1 X10 Y10 ; Complete slot rectangle
G0 Z5 ; Retract tool

Example

This example mills a rectangular slot 40mm long, 10mm wide, and 2mm deep. It starts by moving the tool above the slot, plunges into the material, cuts the slot perimeter, and then retracts.

gcode

G21 ; Set units to millimeters
G90 ; Absolute positioning
G0 X10 Y10 Z5 ; Move above slot start
G1 Z-2 F100 ; Plunge 2mm deep
G1 X50 Y10 F200 ; Cut slot length
G1 X50 Y20 ; Cut slot width
G1 X10 Y20 ; Cut back width
G1 X10 Y10 ; Close slot
G0 Z5 ; Retract tool
M30 ; Program end

Common Pitfalls

Common mistakes when milling slots include:

• Not setting the correct Z depth, causing incomplete cuts or tool damage.
• Using G0 (rapid move) for cutting moves, which can damage the tool or material.
• Forgetting to set the feed rate F during cutting moves.
• Not retracting the tool safely after cutting.

Always use G1 for cutting moves with a proper feed rate and confirm the depth is safe for your tool and material.

gcode

Wrong:
G0 Z-2 ; Rapid plunge (dangerous)
Right:
G1 Z-2 F100 ; Controlled plunge

Quick Reference

Command	Description
G0	Rapid move (no cutting)
G1	Linear cutting move with feed rate
X, Y	Horizontal coordinates
Z	Vertical coordinate (depth)
F	Feed rate (cutting speed)
G21	Set units to millimeters
G90	Absolute positioning mode
M30	End of program

Key Takeaways

Use G1 with feed rate for all cutting moves to mill slots safely.

Start with G0 to position the tool above the slot before plunging.

Set the correct Z depth to avoid tool damage or incomplete cuts.

Always retract the tool with G0 after finishing the slot.

Use absolute positioning (G90) and millimeter units (G21) for clarity.