G-Code for Fusion 360 — How to Verify CAM Output Before Machining

Fusion 360 generates G-code through its CAM environment — you define toolpaths, select a post-processor for your machine, and export an NC file. The result is the actual program that runs on the controller. But how much do you trust it before pressing Cycle Start?

This guide explains what Fusion's built-in simulation does and doesn't verify, and how to add a second layer of validation with a machine-level G-code simulator.

What Fusion 360 Simulates

Fusion 360 has a simulation mode inside the CAM environment (Simulation button in the toolbar). It shows:

The toolpath the CAM system calculated
Material removal based on CAM geometry
Tool, holder, and stock collisions at the CAM level
Cycle time estimates

This is a CAM-level simulation — it verifies the toolpath before post-processing.

What Fusion 360 Does Not Simulate

The NC file that Fusion exports goes through a post-processor — a script that translates Fusion's internal toolpath data into G-code formatted for your specific controller (Fanuc, Haas, Heidenhain, Siemens, etc.).

The post-processor can introduce errors that Fusion's simulator never sees:

Post-processor bugs — incorrect M-code sequences, wrong tool change syntax, missing G49 before G28
Controller-specific behavior — a canned cycle that behaves differently on your Fanuc 30i than in Fusion's generic simulation
Machine kinematics — axis travel limits, tool changer positions, fixture clearances that Fusion doesn't know about
Actual G-code syntax — Fusion simulates the intent of the toolpath, not the literal G-code that the controller will interpret

The gap between "what Fusion simulated" and "what the controller will actually execute" is where crashes happen.

The Eureka3X + Fusion 360 Workflow

Eureka3X includes a native Fusion 360 interface. The workflow:

Program your part in Fusion 360 CAM as normal
Post-process to generate the NC file for your controller
Load the NC file in Eureka3X
Simulate on the full 3D machine model — the same G-code that will run on the machine
Verify collisions, clearances, Z depths, and tool change positions
Run on the machine with confidence

The key difference: Eureka3X simulates the actual NC file — the post-processed G-code — not the CAM toolpath. It interprets G-code the way your controller does.

Common Post-Processor Errors Caught by Eureka3X

Tool change position error — the post-processor outputs G28 in absolute mode (G90 G28 Z0.) instead of incremental (G91 G28 Z0.), causing the Z axis to drive toward the part before going home.

Missing G49 — the post-processor forgets to cancel tool length compensation before a tool change, causing the next tool's Z positions to be offset by the previous tool's length.

Incorrect canned cycle syntax — a generic post for Fanuc outputs G84 without checking whether the machine requires M29 for rigid tapping.

Wrong work offset — the post outputs G54 but the machine is set up in G55. The program runs in the wrong location.

Feed rate in wrong units — the post outputs mm/min feed rates but the machine is in inch mode (G20 active from a previous program).

All of these produce errors that are invisible in Fusion's CAM simulation but immediately visible in Eureka3X, because Eureka3X runs the actual G-code against the actual machine model.

Setting Up the Fusion 360 Interface in Eureka3X

Eureka3X includes a free Fusion 360 add-in that streamlines the workflow:

Install the Eureka3X add-in from the Fusion 360 App Store (or from the link in your Eureka3X account)
In Fusion CAM, select Post Process → Eureka3X
The NC file is automatically sent to Eureka3X for simulation
Review the simulation, verify clearances, and approve before sending to the machine

This eliminates the manual export-import step and keeps the workflow inside Fusion's environment.

What to Check in the Simulation

When reviewing your Fusion 360 output in Eureka3X, focus on:

Tool change sequence — verify Z retracts to machine home before M06, and that the new tool's G43 offset is correct.

First cut approach — verify the approach from the tool change position to the first cut does not pass through the fixture or part.

R-plane heights — in canned cycles, verify R is above the part surface at all hole locations, including holes on raised bosses.

Depth consistency — compare programmed depths against the part geometry to catch unit errors (mm vs inch) or wrong Z datum.

Rapid moves between operations — Fusion's post-processor may output rapid moves that clear the stock but not the fixture. Eureka3X shows the fixture in the simulation.

AI-Generated G-Code from Fusion

Fusion 360 increasingly incorporates AI-assisted toolpath generation. AI-generated toolpaths are more likely to produce post-processor output that requires verification — the AI optimizes for geometry but has no knowledge of your specific machine's kinematics, parameter settings, or controller dialect.

Running AI-generated Fusion output through Eureka3X before machining is particularly important for this reason.

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