Fillet Corners on a Rectangle in FreeCAD Sketch

This guide provides a straightforward method for creating filleted corners on a rectangle within FreeCAD's Sketcher workbench. You will learn how to activate the Fillet tool, apply rounded corners to intersecting lines or vertices, and apply constraints to ensure your sketch remains stable and fully defined.

Step 1: Open the Sketch and Draw a Rectangle

  1. Double-click your sketch in the Tree View to enter edit mode in the Sketcher workbench.
  2. If you have not already created a rectangle, select the Create rectangle tool from the toolbar (or press G then R) and place it in the sketch window.

Step 2: Select the Sketcher Fillet Tool

  1. In the top toolbar, find and click the Create a fillet icon (represented by an arc connecting two perpendicular lines).
  2. Alternatively, you can access it via the menu bar by navigating to Sketch > Sketcher geometries > Create fillet or by pressing the shortcut key F.

Step 3: Apply the Fillet to the Corners

There are two ways to apply the fillet using the tool:

  • Method 1 (Selecting Lines): Click the first edge of the corner, then click the adjacent perpendicular edge. A curved arc will replace the sharp corner.
  • Method 2 (Selecting the Vertex): Click directly on the corner vertex point. FreeCAD will automatically trim the intersection and insert the fillet arc.

Repeat this process for any other corners you wish to round.

Step 4: Constrain the Fillet Radius

Once the fillets are created, they will be unconstrained by default:

  1. Select the arc of one of the filleted corners.
  2. Click the Constrain radius tool in the toolbar (or press Shift + R).
  3. Enter your desired radius value in the pop-up dialog and click OK.

Step 5: Equalize Remaining Corners (Optional)

To make all four corners identical without manually setting the radius on each one:

  1. Select all the fillet arcs by holding Ctrl and clicking each arc.
  2. Click the Constrain equal tool (or press E).
  3. All selected corners will now match the radius of the dimensioned fillet. Changing the primary radius will automatically update the others.