Capstok — learn by doing

Why this matters

Every print job is just a long text file of G-code commands. Understanding the basic commands — and being able to read/write them manually — lets you diagnose what the slicer told the printer to do, write custom start/end sequences, and use the printer as a controllable machine for tasks like dispensing or pen-plotting.

Demo

The G-code commands you'll see every print.

Try it yourself

Open a sliced G-code file in a text editor. Skip past the header; you'll see thousands of G1 commands. Pick one and identify what it does.
Write a custom start G-code that prints your name on the LCD via M117. Add it to your slicer's start script.
Use Pronterface or your slicer's terminal to send M201 (max acceleration). What does your printer respond with?

Prompt your AI

Use these three in order. Each builds on the one before.

1. Basics & terminology

In one paragraph, explain what G-code is and why every printer uses it.

2. Why it works (the mechanism)

Walk me through what each command in a typical print's first 20 lines does.

3. Advanced — application & what's next

Design a custom start G-code that warms up, homes, levels, and 'nozzle wipes' the bed before printing.

References

; A typical print starts with setup commands:
G90                ; absolute positioning
M83                ; relative extruder mode (sliced files usually use this)
M104 S210          ; set hotend temp to 210C (no wait)
M140 S60           ; set bed temp to 60C (no wait)
M109 S210          ; wait for hotend to reach 210C
M190 S60           ; wait for bed to reach 60C
G28                ; home all axes
G29                ; auto-bed-level (build mesh)

; Then comes the print itself, generated by the slicer:
G1 X10 Y10 Z0.2 F3000     ; move to start of layer 1, no extrusion
G1 X100 Y10 E5.0 F600     ; extrude 5mm of filament while moving in X
G1 Z0.4 F600              ; move up to layer 2
...
; Thousands of these for a typical print.

; End of print:
M104 S0            ; turn off hotend
M140 S0            ; turn off bed
G91                ; relative positioning
G1 Z10             ; raise nozzle 10mm
G90                ; absolute positioning
G28 X Y            ; home X and Y (presents print)
M84                ; disable motors

; Common commands you'll write yourself:
M117 "Hello!"      ; display message on LCD
M601                ; pause print
M600                ; filament change (color swap)
M84                ; disable motors (useful for filament inspection)
G92 E0              ; reset the extruder position counter
M220 S100           ; flow rate at 100% (adjust mid-print to fix under/over extrusion)
M221 S100           ; feed rate at 100% (adjust mid-print to speed up/slow down)

In Klipper, many of these are replaced with macros like:
  M104 -> SET_HEATER_TEMPERATURE HEATER=extruder TARGET=210
  G29 -> BED_MESH_CALIBRATE
But Klipper still parses standard G-code for compatibility.

G-code: The Language Your Printer Speaks