How to Verify Additive Manufacturing G-Code

The difference between a successful 18-hour 3D print and an expensive tangle of plastic often comes down to one critical step: G-code verification.

In additive manufacturing, a slicer translates your 3D digital model into G-code—the machine language of coordinates, speeds, temperatures, and extrusion rates. Because slicers are automated algorithms, they can occasionally misinterpret geometry, generate floating overhangs, or introduce travel moves that risk colliding with the print. Verifying your G-code before hitting “Print” safeguards your time, material, and equipment.

Core Methods for G-code Verification

Verifying G-code involves a blend of visual simulation, parameter checking, and hardware-level dry runs. Here is how engineers and makers systematically audit their print files:

1. Layer-by-Layer Simulation (Visual Inspection)

Most modern slicers (like PrusaSlicer, Cura, or Bambu Studio) and standalone G-code viewers (such as NC Viewer or Repetier-Host) include a preview mode.

• Scrub the Z-axis: Manually slide the layer height indicator from bottom to top. Look closely at the first layer to ensure proper adhesion lines, and check mid-print layers for sudden gaps, unsupported overhangs, or missing infill connections.
• Inspect Feature Types: Color-code your preview by feature (perimeters, external walls, internal infill, support material) to verify that critical structural paths are being laid down correctly.

2. Code-Level Parameter Audit

For high-reliability or industrial additive manufacturing, visual checks aren’t always enough. A quick scan of the raw text file (or using automated pre-flight checks) helps verify parameters:

• Temperature Commands: Check M104 or M109 (hotend temperature) and M140 or M190 (bed temperature) to ensure they match your filament or powder specifications.
• Extrusion Multipliers and Flow: Look for unusual G1 E... values that could cause under- or over-extrusion.
• Start and End G-code Macros: Ensure homing commands (G28) are present at the beginning and proper retraction/cooling macros occur at shutdown.

3. Collision and Travel Path Checking

Unnecessary or erratic travel moves can cause the nozzle or laser head to clip already-printed sections of the model.

• Watch out for “travel through print” behaviors where the toolhead crosses open air or solid geometry unnecessarily.
• In advanced multi-axis or robotic additive manufacturing, dedicated CAM simulation software is mandatory to simulate kinematics and prevent mechanical singularity collisions.

4. The “Dry Run” Test

If you are working with a new setup, complex geometry, or experimental parameters, perform a dry run:

• Run the G-code with the heating elements turned off or set to room temperature, and keep filament unloaded (or execute an air-print well above the bed).
• Keep your hand near the emergency stop or power switch to verify that physical axis limits, endstops, and clearances behave precisely as simulated.

Taking two minutes to review your toolpaths in a G-code visualizer transforms guesswork into precision engineering, ensuring every layer lands exactly where it belongs.