How to Simulate CNC Machining in FreeCAD Path

Simulating CNC toolpaths in FreeCAD allows you to verify cutting sequences, inspect raw stock removal, and detect errors or collisions before exporting G-code to a physical machine. This guide outlines the exact steps to configure, launch, and control the simulation tool within FreeCAD's CAM (formerly Path) Workbench to validate your machining jobs safely.

1. Prepare Your CAM Job

Before running a simulation, you must have an active CAM Job with configured operations:

  1. Open your 3D model and switch to the CAM (or Path) Workbench from the workbench dropdown.
  2. Ensure you have created a Job containing your base model, defined stock boundaries, and appropriate tool controller definitions.
  3. Verify that your cutting operations (such as Profile, Pocket, or Adaptive) are fully computed and visible under the Job tree hierarchy.

2. Launch the CAM Simulator

  1. In the Tree View, click on the Job container or select the specific operations you want to inspect.
  2. Click the CAM Simulator icon on the toolbar (depicted as a cutting tool removing material from a stock cube), or navigate to the top menu and select CAM > CAM Simulator.
  3. FreeCAD will render a semi-transparent representation of your defined stock over your base part.

3. Configure the Simulation Controls

Once the simulator panel opens in the Tasks tab on the left:

  • Playback Speed: Adjust the slider to increase or decrease the animation speed of the cutting head.
  • Accuracy/Resolution: Set the mesh resolution. Higher accuracy provides a more precise representation of the finished surface but may reduce playback performance on older hardware.

4. Run and Analyze the Toolpath

  • Click the Play button to begin the virtual machining process.
  • Use the Pause and Step Forward controls to inspect complex geometries or deep passes frame-by-frame.
  • Rotate and zoom your view in the 3D viewport while the simulation is running or paused to check undercut areas, entry plunges, and tab placements.
  • Pay close attention to red lines or warnings indicating rapid movements (G0) traveling through uncut material rather than above the clearance plane.

5. Finalize and Correct Errors

When the animation finishes, compare the remaining stock volume against your original 3D geometry to ensure all necessary features were machined correctly. Click OK or Close in the Tasks tab to exit the simulator. If you spot gouges, uncut stock, or rapid-traverse collisions, reopen the problematic operation in the Tree View to modify depths, step-overs, or retract heights before running the simulation again.