G-code and 3D Printing Development Standards

Thermal Runaway and Heating Safety

• Never attempt to manually override or disable firmware-level thermal runaway protection via G-code. This protection is

a critical safety feature that prevents fires.

• Use blocking temperature commands before any extrusion sequence:
• M109 S<temp>: wait for hotend to reach target temperature.
• M190 S<temp>: wait for heated bed to reach target temperature.
• Do not use the non-blocking variants (M104 / M140) as the sole heat command before extrusion; cold extrusion

shreds filament or breaks the extruder gear.

• Enforce maximum temperature bounds based on the printer's hardware:
• PTFE-lined hotends: strictly limit to a maximum of 230°C to prevent off-gassing of toxic fumes (PTFE decomposition

begins above 240°C).

• All-metal hotends: respect the manufacturer's stated maximum.
• Use M303 E0 S<target_temp> C8 PID auto-tuning to establish stable thermal profiles before committing a new filament

profile to production G-code.

Coordinate Systems and Positioning

• Declare the positioning mode explicitly at the beginning of every G-code sequence. Never rely on the machine's assumed

default state.

• Set all structural and toolhead movements to Absolute Positioning: G90.
• Explicitly declare the extruder positioning mode:
• M82: Absolute Extrusion (E-values are cumulative totals).
• M83: Relative Extrusion (E-values are per-move deltas).
• The chosen mode must exactly match the logic used to calculate filament E-steps in the slicer profile.
• Use Relative Positioning (G91) only for immediate toolhead micro-moves such as Z-hop, then immediately return to

G90 (Absolute).

Crash Prevention and Physical Boundaries

• Require a mandatory homing command (G28 or G28 XYZ) before any XYZ movement commands (G0 or G1). Never command

a move when the machine's absolute position is unknown.

• Enforce software limit bounding: be provided the exact build volume (e.g., X: 220, Y: 220, Z: 250) and never generate

coordinates that exceed these limits to prevent stepper motor crashes and belt skipping.

• Mandate Z-hop during long travel moves over already printed areas:

  G91           ; relative
  G1 Z0.4 F600  ; lift
  G90           ; absolute
  G0 X... Y...  ; travel
  G91
  G1 Z-0.4 F600 ; lower
  G90

This prevents the hot nozzle from colliding with and dislodging the printed part.

Firmware Specifics, Marlin vs. Klipper

• When targeting Klipper, prohibit raw G-code logic for complex processes (tool changes, filament runout, mesh

levelling). Invoke safe, pre-configured Jinja2 macros instead:

• START_PRINT BED_TEMP=60 EXTRUDER_TEMP=215
• END_PRINT
• PAUSE, RESUME, CANCEL_PRINT
• All feedrate F values in G0 and G1 commands must be in millimeters per minute (mm/min), not mm/s. (600 mm/min =

10 mm/s.)

• Add explicit M400 (wait for moves to finish) before tasks that require the toolhead to be physically stopped (camera

snapshot, macro execution, pause).

Filament Calibration Requirements

Before generating production G-code for a new filament profile, perform and record the following calibrations:

• Pressure Advance (Klipper) / Linear Advance K-factor (Marlin): tune for the specific filament and hotend combination

to eliminate corner bulge and improve dimensional accuracy.

• Klipper: SET_PRESSURE_ADVANCE ADVANCE=<value>
• Marlin: M900 K<value>
• Extrusion Multiplier (EM): calibrate via a single-wall cube; target wall thickness must match the configured line

width within ±2%.

• Retraction: tune retraction distance and speed for the specific extruder type:
• Direct drive: typically 0.5-2.0 mm.
• Bowden: typically 4-7 mm.
• Objective: eliminate stringing between features.
• Store all calibrated profile values in a version-controlled slicer profile file alongside the G-code output.

Start G-code, Bed Mesh and Purge Line

Every start G-code sequence must follow this pattern:

1. Home all axes: G28.
2. Load bed mesh / run auto-levelling:

• Klipper: BED_MESH_CALIBRATE or BED_MESH_PROFILE LOAD=default.
• Marlin UBL/BLTouch: G29.

1. Never hard-code a Z-offset value in generated G-code; always read it from the printer's saved configuration.
2. Generate a purge line on an edge of the bed, outside the print area to prime the nozzle before the first print move.

Never purge over the area where the part will be printed.

Example purge line (left edge, outside print area):

G1 X1 Y20 Z0.3 F5000   ; move to purge start
G1 E10 F300             ; prime
G1 Y180 E25 F1500       ; draw purge line
G1 Z2 F3000             ; lift

Post-Processing G-code Patterns

• Fan ramp: set fan to 0% for the first two layers, then ramp to 100% (or profile-defined value) from layer 3 onward

using layer-change hooks.

  ; Layer 1-2: M107 (fan off)
  ; Layer 3+:  M106 S255 (full fan)

• Seam placement: position seams at the rear of the model or at a sharp corner to minimise visibility.
• Use G10 / G11 (Firmware Retract) only when the printer's firmware retract values are fully tuned; otherwise use

explicit E-axis retract moves for reproducibility.

Multi-Material Print Standards

• Define a dedicated TOOL_CHANGE macro in Klipper (or T0/T1 sequences in Marlin) for each extruder. Never generate

raw inline tool-change sequences without invoking the printer's macro.

• Always include a purge/prime tower or purge bucket wipe sequence after every tool change to clear residual filament

colour from the nozzle.

• Set independent temperature targets per tool (T0 and T1); ensure both nozzles reach target temperature before

beginning the tool-change sequence.

Slicer Profile Version Control

• Store all slicer profiles in the project's Git repository under slicer-profiles/:
• PrusaSlicer: .ini
• OrcaSlicer: .json
• Cura: .cfg / .curaprofile
• Name profile files with the filament type, nozzle size, and layer height:

  pla-0.4mm-0.2mm-layer.ini
  petg-0.6mm-0.3mm-layer.json

• Tag the slicer profile version in the G-code file header comment so any printed part can be exactly reproduced:

  ; Profile: pla-0.4mm-0.2mm-layer.ini v1.3
  ; Slicer: OrcaSlicer 2.1.0
  ; Printer: Voron 2.4 350mm
  ; Date: 2025-03-01

Emergency Stop and Safety Halts

• Insert ; VERIFY: <instruction> comments as operator checkpoints in generated G-code sequences that require hardware

state verification (bed clear, filament loaded) before proceeding.

• Use M112 (emergency stop) as the abort command in scripts that detect a fatal error condition. Understand that

M112 immediately cuts power to all motors and heaters and requires a firmware restart.

• Never generate G-code that commands G1 Z0 or moves toward Z=0 without a prior G28 Z home; a Z-crash with a loaded

bed damages the print surface and the nozzle.