G-code

Definition

G-code is a numerical control programming language — essentially a text file containing a series of “coordinate + action” instructions. In 3D printing, the slicer converts 3D model files (STL, OBJ, etc.) into G-code, and the printer’s controller reads and executes these instructions line by line to complete the print.

Simple Analogy

Imagine writing an extremely detailed navigation manual for a robot: “Move forward 10 cm, turn right 90 degrees, move forward 5 cm, stop, extrude some sauce…” G-code is exactly that instruction manual for the printer, except the coordinates are accurate to micrometers and the actions are timed to milliseconds.

Why It Matters

G-code is the bridge that connects “digital model” and “physical print.” Here are a few key G-code commands every 3D printing enthusiast should know:

Command	Meaning
G1 X10 Y20 E5	Linear move to (10, 20) while extruding 5 mm of filament
G28	Home all axes
G29	Run auto bed leveling
M104 S200	Set nozzle temperature to 200°C
M140 S60	Set bed temperature to 60°C
G91 / G90	Switch to relative/absolute coordinate mode

Practical Advice

Most regular users don’t need to and shouldn’t manually edit G-code — the slicer automatically generates optimal code. But knowing G-code can save you in these situations:

1. Printer starts with nozzle in the wrong position: Check if G28 (homing) is included in the start G-code.
2. Nozzle stays on the model after printing: Add G1 Z{layer_height+10} to the end G-code to raise the nozzle.
3. Need custom actions like filament change or pause: Insert the corresponding M-code in the slicer’s “Custom G-code” section.

We recommend starting your learning by reading the beginning of any .gcode file generated by your slicer — it contains all the startup procedures (heating, leveling, purging) in plain text. Reading through it once will show you exactly what your printer is doing after you hit “start print.”