How to Verify Additive Manufacturing G-Code

From Slicer to Reality: A Complete Guide to Verifying Additive Manufacturing G-Code

In additive manufacturing, your G-code is the definitive bridge between a pristine digital computer-aided design (CAD) model and a physical, functional part. Whether you are running a desktop fused deposition modeling (FDM) machine or an industrial selective laser melting (SLM) system, the G-code dictates every movement, temperature adjustment, and extrusion rate.

A single misplaced coordinate, incorrect temperature command, or rogue retraction setting can turn a 24-hour print into a tangled mess of plastic or a damaged build plate. Verifying your G-code before hitting “Print” is not just a best practice—it is an essential quality control step.

1. Understanding the Anatomy of AM G-Code

Before diving into verification tools, it helps to understand what you are looking at. Unlike traditional CNC machining where G-code commands linear and rotational cuts, additive manufacturing G-code focuses on extrusion rates, volumetric flow, deposition paths, and thermal management.

Key command families to watch for include:

• Motion Commands: G0 (Rapid move / travel) and G1 (Controlled linear move / printing).
• Positioning Modes: G90 (Absolute positioning) and G91 (Relative positioning).
• Extrusion & Material: M82 / M83 (Absolute/Relative extrusion) and E parameters dictating filament feed length.
• Thermal Control: M104 / M109 (Hotend temperature) and M140 / M190 (Print bed temperature).

2. Essential Verification Methods and Tools

Catching errors digitally saves valuable material, machine time, and operator headaches. A robust verification workflow relies on a mix of text inspection and visual simulation.

Visual Simulators and Viewers

Never rely solely on your slicer’s internal preview. Exported G-code can sometimes harbor translation errors or post-processing script bugs. Use dedicated G-code viewers (such as NC Viewer, GCodeViewer, or software built into printer firmware like Klipper or RepRapFirmware interfaces) to inspect the toolpath.

• Layer-by-Layer Scrubbing: Scroll through individual layers to check for floating islands, sudden jumps in travel moves, or un-supported overhangs.
• Retraction and Travel Inspection: Look for excessive stringing paths or unoptimized travel moves that cross over visible outer perimeters.

3. The Pre-Flight G-Code Verification Checklist

Before sending any file to production, run it through this systematic checklist:

| Verification Step | What to Check | Potential Risk if Ignored |
| :— | :— | :— |
| Header & Initialization | Confirm bed leveling routines, purging lines, and proper tool/extruder selection. | Head crashes into the bed or printing off-center. |
| Temperature Profiles | Verify that M109 and M190 commands match the manufacturer’s material datasheet. | Cold extrusion jams, thermal degradation, or poor layer adhesion. |
| Bounding Box & Limits | Ensure the total coordinate extents (X, Y, Z) fit safely within your printer’s build volume. | Mechanical limit switch hits, axis stalling, or stepping loss. |
| Post-Processing Scripts | Check custom scripts (