How to Perform Facing Operation in FreeCAD

Performing a facing operation in FreeCAD prepares raw stock by machining the top surface flat and bringing the material down to the exact final Z-height. Using the CAM Workbench (formerly called the Path Workbench in earlier versions), you define your raw stock dimensions, set tool parameters, and apply the MillFace operation to generate clean toolpaths across the material. This guide covers the complete step-by-step process to set up your stock, configure the facing toolpath, simulate the cut, and export G-code.

1. Switch to the CAM Workbench

Open your 3D model in FreeCAD. From the workbench dropdown menu at the top of the interface, switch to the CAM (or Path) workbench.

2. Create and Configure a Job

Before generating any toolpaths, you must define the machine setup and the raw material bounds.

  1. Click the Job button on the CAM toolbar.
  2. Under the Geometry tab, ensure your part is selected.
  3. Switch to the Output tab to specify your post-processor based on your CNC controller (e.g., LinuxCNC, GRBL, Mach3).
  4. Switch to the Setup tab to define your raw stock:
    • Select Create Box.
    • Add extra material to the stock margins, particularly along the Z+ axis (e.g., 1.0 mm to 2.0 mm), which represents the raw stock material that the facing operation will remove.
  5. Switch to the Tools tab, click Add, and choose an appropriate tool (typically a flat end mill or dedicated face mill) from your tool library.
  6. Click OK to create the Job.

3. Create the MillFace Operation

  1. Select the top horizontal face of your 3D model in the viewport.
  2. Click the MillFace button on the CAM toolbar. FreeCAD will create a facing operation linked directly to the selected surface.

4. Configure the Facing Parameters

Double-click the newly created Facing operation in the tree view to open the Data properties:

  • Depths Tab:
    • Start Depth: Set this to the top of your raw stock (equal to the model height plus your added Z+ margin).
    • Final Depth: Set this to the top surface of the finished model (typically 0.0 mm relative to the selected face).
    • Step Down: Specify the maximum depth per pass (e.g., 0.5 mm) depending on your material hardness and tool capabilities.
  • Heights Tab:
    • Verify that the Clearance Height and Safe Height are set high enough to clear any clamps or fixtures.
  • Operation Tab:
    • Pattern: Choose a cutting strategy, such as ZigZag (bi-directional) or Line (uni-directional for better surface finishes).
    • Step Over: Set the radial stepover percentage (commonly 50% to 75% of tool diameter).
    • Boundary Shape: Choose Stock rather than Bound if you want the cutter to clean the entirety of the oversized raw material, not just the model footprint.

Click Apply, then OK to compute the toolpath.

5. Simulate and Verify the Toolpath

  1. Select your Job in the tree view.
  2. Click the CAM Simulator button on the toolbar.
  3. Adjust the playback speed and press Play to visually inspect the cutting passes. Ensure the tool covers the full area of the raw stock and steps down progressively without colliding with the part.

6. Post-Process (Export G-Code)

Once verified, select the Job or the specific Facing operation and click the Post-Process button on the toolbar. Save the generated .nc or .gcode file to send directly to your CNC machine.