How to Create a Tapered Extrusion in FreeCAD

Creating a tapered extrusion in FreeCAD allows you to produce draft angles on 3D models, which is essential for injection molding, casting, or specific aerodynamic and aesthetic shapes. This guide outlines the most straightforward methods to achieve a tapered extrusion using the native Part Design workbench, the Part workbench, and the Loft tool for more advanced geometries.

The standard and most parametric way to create a tapered solid is through the Part Design workbench using the Pad feature.

  1. Create a Body and Sketch: Open the Part Design workbench. Click Create body, then click Create sketch. Select your desired plane (e.g., XY-plane), draw your profile, fully constrain it, and close the sketch editor.
  2. Open the Pad Tool: With the sketch selected in the tree view, click the Pad tool from the toolbar.
  3. Set the Extrusion Length: In the Tasks panel on the left side of the screen, define the standard extrusion distance under Length.
  4. Adjust the Taper Angle: Locate the Taper angle field in the Pad parameters.
    • Enter a positive angle to taper the extrusion outward as it extends.
    • Enter a negative angle to taper the extrusion inward.
  5. Confirm the Pad: Click OK to apply the extrusion.

Method 2: Using the Part Workbench Extrude Tool

If you are working outside the Part Design workflow with standalone 2D shapes or surfaces, use the Part workbench.

  1. Switch Workbenches: Select the Part workbench from the workbench dropdown menu.
  2. Select the Profile: Click on the 2D sketch, face, or wireframe you want to extrude.
  3. Launch Extrude: Click the Extrude icon in the toolbar.
  4. Configure Parameters: In the extrusion settings, set your direction vector and length.
  5. Apply Taper: Set the desired degrees in the Taper angle input field.
  6. Finalize: Click OK to generate the tapered solid.

Method 3: Using an Additive Loft (For Complex Tapers)

If your taper requires different profile shapes at each end, or non-uniform draft angles, use a loft instead of a simple extrusion.

  1. Create the Base Sketch: In the Part Design workbench, draw your base profile.
  2. Create an Offset Datum Plane: Create a Datum Plane offset along the Z-axis (or the normal axis of your base sketch) to define the height of the extrusion.
  3. Create the End Sketch: Create a second, scaled sketch on the new datum plane representing the top of the taper.
  4. Apply Additive Loft: Select the base sketch, click Additive Loft, click Add Section, and select the second sketch. Click OK.

Important Considerations

  • Self-Intersection Errors: If you use a negative taper angle that is too steep for the specified length, the geometry will collapse into itself at the apex and fail to render. If the tool fails, decrease the taper angle or reduce the extrusion length.
  • Complex Profiles: Sharp internal corners with steep taper angles can cause self-intersecting faces. Adding fillets to sharp corners in your initial sketch often resolves geometry generation errors.