How to Create a Boss Feature in FreeCAD

This guide explains how to add a raised boss feature to any flat surface on an existing 3D model using FreeCAD's Part Design workbench. A boss is a common mechanical feature used to accept fasteners, provide alignment, or reinforce mounting points. By selecting the target face, drawing a constrained sketch, and using the Pad tool, you can quickly integrate a boss directly into your solid body.

Step 1: Open the Part Design Workbench

  1. Open your project in FreeCAD.
  2. In the workbench dropdown menu at the top of the interface, switch to the Part Design workbench.
  3. Ensure that the active Body containing your part is highlighted in bold in the Tree view. If not, double-click the Body to activate it.

Step 2: Select the Target Flat Face

  1. In the 3D viewport, click directly on the flat face where you want the boss to be located.
  2. The selected face will highlight (typically turning green or light blue).

Step 3: Create a Sketch on the Face

  1. With the face selected, click the New sketch tool (the icon featuring a red circle and rectangle) on the toolbar.
  2. FreeCAD will create a sketch mapped directly to that planar surface and orient the camera normal to the face.

Step 4: Draw and Constrain the Boss Profile

  1. Select the Create circle tool from the sketcher toolbar (or use another geometric shape if your boss is non-cylindrical).
  2. Click to place the center point and drag to define the approximate radius.
  3. If you need to position the boss relative to existing edges, use the External Geometry tool (icon with a blue edge/cube) to select the reference edges or vertices from the model.
  4. Apply geometric and dimensional constraints:
    • Constrain the diameter or radius of the circle using the Diameter constraint or Radius constraint tool.
    • Constrain the distance of the center point from your external geometry or sketch axes using horizontal and vertical distance constraints.
  5. Once the sketch turns fully green (indicating it is fully constrained), click the Close button in the Tasks panel.

Step 5: Pad the Sketch to Form the Boss

  1. With the newly created sketch selected, click the Pad tool in the Part Design toolbar.
  2. In the Tasks panel on the left, enter the desired Length (height) for the boss.
  3. Ensure the direction extends outward from the surface. If it extends inward, check the Reversed checkbox.
  4. Click OK to finish.

The boss is now merged into the existing solid body. If a fastener hole is required through the center of the boss, you can select the top face of the new boss and use either the Hole feature or sketch an inner circle and apply a Pocket.