FreeCAD Path 3D Surface Milling Guide

Performing a 3D surface contour milling operation in FreeCAD allows you to machine complex, curved, and non-planar geometries directly from your 3D models. This guide outlines the complete workflow for setting up your model in the Path (now CAM) workbench, creating a dedicated 3D Surface operation, configuring critical toolpath parameters such as stepover and cut patterns, and inspecting the generated toolpaths for accurate CNC production.

1. Switch to the CAM/Path Workbench and Create a Job

  1. Open your 3D solid model in FreeCAD.
  2. In the workbench dropdown menu, select CAM (or Path in older FreeCAD versions).
  3. Click the Job button in the toolbar to create a new machining project.
  4. In the Job dialog:
    • Select your solid model as the base object.
    • On the Stock tab, define your stock dimensions (add margin if necessary).
    • On the Tools tab, assign a tool controller (typically a ball nose end mill is best suited for 3D curved surfaces).
    • Confirm the setup by clicking OK.

2. Add the 3D Surface Operation

  1. Ensure your Job is active in the model tree.
  2. In the top menu, navigate to CAM (or Path) > 3D Surface, or click the 3D Surface icon in the toolbar.
  3. A new dialog will open with several configuration tabs: Base Geometry, Depths, Heights, and Operation.

3. Define Geometry and Bound Box

  1. Go to the Base Geometry tab.
  2. If you want to mill specific faces rather than the entire model:
    • Select the target curved faces on your 3D model in the viewport.
    • Click the Add button in the Base Geometry list.
  3. If no specific faces are selected, FreeCAD will use the entire bounding region of the model.
  4. On the Operation tab, configure the BoundBox setting:
    • Choose Base Geometry to constrain tool movement only to the selected faces.
    • Choose Stock to cover the entire work area.

4. Configure Machining Parameters

Switch to the Operation tab to refine how the cutter moves over the surface:

  • Cut Mode: Select Climb, Conventional, or ZigZag depending on your material and tooling requirements. ZigZag minimizes rapid travel moves.
  • Pattern: Choose a scanning strategy. Common options include:
    • Line: Scans back and forth across a specified axis (set via the Drive Line Direction property).
    • Circular or Spiral: Useful for round or contoured parts.
  • Step Over: Set the horizontal distance between adjacent cutting passes. For 3D surfacing with a ball end mill, a smaller stepover (e.g., 5% to 15% of tool diameter) reduces the height of remaining cusps and provides a smoother finish.
  • Step Down: Set the maximum vertical depth the tool can remove per pass. If roughing has already cleared bulk material, this can be set to the full depth of the target contour.
  • Sample Interval: Determines the resolution of the surface calculation. Smaller values yield more accurate toolpaths along intricate curves at the cost of longer computation times.

5. Set Depths and Clearance Heights

  1. Open the Depths tab to define the Start Depth and Final Depth. Set the Final Depth to the lowest point of your contour.
  2. Open the Heights tab to ensure the Clearance Height and Safe Height provide adequate clearance above clamps and fixtures.

6. Generate and Inspect the Toolpath

  1. Click Apply and then OK to generate the toolpath.
  2. Inspect the green toolpath lines directly in the 3D viewport to ensure the cutter stays within the intended boundaries.
  3. Select the CAM Job in the tree and click the CAM Simulator button to run a virtual simulation of the cutting process to verify that there are no gouges, unexpected rapid moves, or collisions.