How to Fillet Edges in FreeCAD Part Workbench

This article provides a direct guide on how to fillet edges directly on a 3D solid using the Part workbench in FreeCAD. You will learn the step-by-step process of selecting a shape, launching the Fillet tool, picking specific edges or faces, adjusting the radius, and troubleshooting common geometric errors that can cause the operation to fail.

Step 1: Switch to the Part Workbench

  1. Open your project in FreeCAD containing the 3D solid you want to modify.
  2. In the workbench selector dropdown at the top of the interface, select Part.

Step 2: Open the Fillet Tool

There are two primary ways to initiate the fillet operation:

  • Method A (Pre-selection): In the 3D view, hold Ctrl and click on the specific edge(s) of your shape that you want to round. Then, click the Fillet icon on the Part toolbar (represented by a rounded corner) or go to Part → Fillet from the top menu.
  • Method B (Panel selection): Ensure your solid is visible. Click the Fillet tool directly from the toolbar without selecting edges first. The Fillet tools panel will open in the Tasks tab on the left sidebar.

Step 3: Configure Edges and Radius

  1. In the Tasks panel, ensure your shape is listed under the shape selection section.
  2. Under the selection list, you will see a list of edges. You can check the boxes next to the edges you want to round, or use the Select edges button to click edges directly in the 3D view.
  3. In the Fillet type section, ensure Constant radius is selected (default).
  4. Enter your desired dimension in the Radius field (for example, 2.00 mm).

Step 4: Apply the Fillet

  1. Click OK at the top of the Tasks panel.
  2. FreeCAD will generate a new parametric feature labeled Fillet in the Model tree, hiding the original shape beneath it.

Tips for Avoiding Fillet Errors

  • Radius Size: The radius must not exceed the dimensions of adjacent geometry. If two filleted edges overlap or if the radius is larger than the face it borders, the operation will fail with a topological error.
  • Order of Operations: If you are filleting intersecting corners, select all intersecting edges at once in the same Fillet operation to allow FreeCAD to generate a smooth corner transition.
  • Editing: To change the radius later, double-click the Fillet object in the Model tree to reopen the Tasks panel, adjust the radius value, and click OK.