# G Code 3d Printing > G-code and 3D printing standards for thermal and motion safety, absolute positioning, Klipper macros over raw G-code, start and end sequences with bed mesh and purge line, filament calibration, and slicer profile version control. Use when you say "write start G-code for my printer", "my nozzle drags through the print", "set up a START_PRINT macro", "calibrate pressure advance", or "version my slicer profiles". Not for the PCB inside the printed part, use `kicad`. - Skill: `lukk17/g-code-3d-printing` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add lukk17/g-code-3d-printing` - Raw SKILL.md: https://api.skillmd.com/api/skills/lukk17/g-code-3d-printing/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Marketing & Growth - Author: Lukk17 (https://skillmd.com/u/lukk17) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/lukk17/g-code-3d-printing --- # G-code and 3D Printing Standards How generated G-code stays safe on real hardware: the machine is never asked to move from an unknown position, never asked to extrude cold, and never asked to override a firmware safety feature. Every rule here maps to a specific way printers catch fire, crash, or ruin a plate. Baseline: Marlin 2.1.x and Klipper current stable. Both accept the standard G-code below, the difference is that Klipper expects complex sequences to live in Jinja2 macros rather than in the slicer. --- ### When to activate - Writing or reviewing start, end, layer-change, or tool-change G-code. - Building or editing a Klipper macro. - Diagnosing a crash, a cold extrusion, a nozzle dragging through a print, or a Z-offset problem. - Calibrating pressure advance, extrusion multiplier, or retraction for a filament. - Version-controlling slicer profiles or embedding a profile reference in output. - Generating or post-processing G-code from a script. --- ### When not to activate - Designing the PCB the printed enclosure houses, use `kicad`. - Writing firmware for the printer's own microcontroller, use `embedded-c-arduino`. - Writing the shell script that uploads or post-processes the file, use `bash` or `powershell`. - Automating the printer from Home Assistant, use `home-assistant`. - Documenting the printer setup for other people, use `markdown-writer`. --- ### Thermal safety Never override or disable firmware thermal runaway protection from G-code. It is the feature that stops a detached thermistor from turning into a fire. Use the blocking heat commands before any extrusion: `M109` waits for the hotend, `M190` waits for the bed. The non-blocking `M104` and `M140` are for starting a heat-up early, never as the only heat command before extruding, because cold extrusion shreds filament and strips the extruder gear. Pass: ```gcode M140 S60 M104 S215 M190 S60 M109 S215 ``` Fail: ```gcode M104 S215 G1 E10 F300 ``` Respect the hardware ceiling: a PTFE-lined hotend stays at or below 230 C, because PTFE decomposition starts above 240 C and off-gasses. An all-metal hotend follows the manufacturer's stated maximum. Run `M303 E0 S C8` PID tuning before committing a new filament profile. --- ### Declare the coordinate mode Never rely on the machine's assumed state. Declare absolute positioning with `G90` and pick the extruder mode explicitly: `M82` for absolute E values, `M83` for relative. The choice must match what the slicer profile computes. Use `G91` only for an immediate micro-move such as a Z-hop, and return to `G90` on the next line. Pass: ```gcode G90 M83 ``` Fail: ```gcode G1 X50 Y50 F3000 ``` --- ### Home before moving, and stay inside the build volume `G28` before any `G0` or `G1`. A move commanded from an unknown position is a crash. Be given the exact build volume and never generate a coordinate outside it. Pass: ```gcode G28 G1 Z5 F600 ``` Fail: ```gcode G1 Z0 F600 ``` Z-hop over already-printed areas so the hot nozzle cannot collide with and dislodge the part: ```gcode G91 G1 Z0.4 F600 G90 G0 X120 Y95 G91 G1 Z-0.4 F600 G90 ``` --- ### Klipper macros over raw sequences On Klipper, tool changes, filament runout, and mesh levelling go through pre-configured Jinja2 macros, so the logic lives in `printer.cfg` under version control rather than being regenerated by every slicer export. Pass: ```gcode START_PRINT BED_TEMP=60 EXTRUDER_TEMP=215 ``` Fail: ```gcode M190 S60 M109 S215 G28 BED_MESH_CALIBRATE G1 X1 Y20 Z0.3 F5000 ``` Feedrate `F` is always millimetres per minute, never mm/s, so 600 is 10 mm/s. Insert `M400` before anything that needs the toolhead physically stopped: a camera snapshot, a macro handoff, a pause. --- ### Start G-code, bed mesh and purge line The sequence is fixed: home, level, heat to the real target, purge outside the part, then print. Never hard-code a Z-offset, read it from the printer's saved configuration. Never purge over the area the part will occupy. Pass, a complete start sequence for a 220 x 220 bed: ```gcode G90 M83 M140 S{bed_temperature} M104 S{first_layer_temperature} G28 M190 S{bed_temperature} M109 S{first_layer_temperature} BED_MESH_PROFILE LOAD=default G92 E0 G1 Z5 F600 G1 X1.0 Y20 Z0.3 F5000 G1 E10 F300 G1 X1.0 Y180 E25 F1500 G1 X1.4 Y180 Z0.3 F5000 G1 X1.4 Y20 E40 F1500 G92 E0 G1 Z2 F3000 ``` On Marlin with UBL or BLTouch, replace the `BED_MESH_PROFILE LOAD=default` line with `G29`. And the matching end sequence, which retracts, lifts, parks clear of the part, and cuts the heaters and motors: ```gcode M400 G91 G1 E-4 F2100 G1 Z10 F600 G90 G1 X5 Y200 F6000 M104 S0 M140 S0 M106 S0 M84 X Y E M117 Print complete ``` Fail, an end sequence that leaves the nozzle sitting on the part with the heaters live: ```gcode M104 S0 M84 ``` The pair belongs together in the slicer profile and in version control. The end sequence retracts before it lifts, so no ooze is dragged across the top surface, and it leaves the Z motor energised so the gantry cannot drop. --- ### Emergency stop and operator checkpoints Insert `; VERIFY: ` comments where the operator must confirm hardware state, bed clear or filament loaded, before the sequence continues. Use `M112` as the abort in any script detecting a fatal condition, and understand that it cuts power to all motors and heaters and needs a firmware restart afterwards. Pass: ```gcode ; VERIFY: bed clear and previous part removed ``` Fail: ```gcode M0 Click to continue ``` --- ### Reference files | Open this | For | |---|---| | [references/calibration-and-profiles.md](references/calibration-and-profiles.md) | Calibrating a new filament, fan and seam post-processing, multi-material tool changes, and slicer profile version control | --- ### Related skills - `kicad` for the board that goes inside the printed enclosure. - `embedded-c-arduino` for firmware on the printer's own controller. - `home-assistant` for automating the printer, its power, and its notifications. - `bash` and `powershell` for upload and post-processing scripts. - `markdown-writer` for the printer and profile documentation. --- ### Checklist - [ ] No G-code overrides or disables a firmware thermal safety feature. - [ ] `M109` and `M190` block before the first extrusion, hotend ceiling respected. - [ ] `G90` and an explicit `M82` or `M83` declared before any move. - [ ] `G28` precedes every XYZ move, and no coordinate leaves the build volume. - [ ] Z-hop wraps every travel move over printed material. - [ ] Complex sequences invoke a Klipper macro rather than inline G-code. - [ ] Start sequence homes, levels, heats, and purges outside the part, with no hard-coded Z-offset. - [ ] End sequence retracts, lifts, parks clear, and cuts heaters and fan. - [ ] Every `F` value is in mm/min. - [ ] Pressure advance, extrusion multiplier, and retraction recorded per filament. - [ ] Slicer profile committed, and its name and version stamped in the G-code header.