How to Combine Multiple Bodies in FreeCAD

Combining multiple independent bodies into a single model in FreeCAD is a common task required for 3D printing, CNC machining, or simplifying your project tree. Depending on whether you want a seamless solid fusion or a grouped assembly, FreeCAD provides dedicated tools in both the Part and PartDesign workbenches. This guide walks you through the most effective methods to merge separate bodies into a unified object.

The most direct way to merge independent bodies—especially those created in different workbenches or separate PartDesign containers—is using the Part Workbench.

  1. Switch Workbenches: In the workbench dropdown menu at the top of the interface, select Part.
  2. Select the Bodies: In the Model tree view on the left, hold down the Ctrl key (or Cmd on macOS) and click on each body you wish to combine. Ensure the bodies intersect or touch if you intend to create a single continuous manifold solid.
  3. Apply the Union: Click the Union icon in the toolbar (represented by two overlapping blue spheres) or navigate to Part > Boolean > Union in the top menu.
  4. Result: A new object named Fusion will appear in your tree view containing the selected bodies. The original bodies will be hidden automatically under this new node.

Method 2: Boolean Operation in the PartDesign Workbench

If you are strictly working inside the PartDesign environment and want to integrate external bodies into an active design body, use the PartDesign Boolean tool.

  1. Activate the Target Body: Double-click the main Body in the tree view that will absorb the other parts. It will become bold, indicating it is active.
  2. Launch the Boolean Tool: Click on the Boolean operation icon in the PartDesign toolbar (two overlapping blue solids) or go to PartDesign > Boolean operation.
  3. Set the Operation: In the Tasks panel, ensure the operation type is set to Fuse.
  4. Add Bodies: Click the Add body button, then click the independent body in the 3D viewport or the tree view. Repeat this for any additional bodies you want to include.
  5. Confirm: Click OK. The selected geometry is now fused directly into your active Body feature tree.

Method 3: Creating a Compound (Non-Destructive Grouping)

If your bodies do not physically touch or you want them saved as a single entity without recalculating their intersecting geometry, you can create a Compound.

  1. Open the Part workbench.
  2. Select all the independent bodies you want to group.
  3. Go to the top menu and select Part > Compound > Make Compound.
  4. A Compound object will be generated. This behaves as a single model for exporting to formats like STEP or STL, while keeping individual sub-shapes distinct.

Exporting Your Unified Model

Once your bodies are combined using either a Fusion, PartDesign Boolean, or Compound:

  1. Click on the resulting parent object (Fusion, Body, or Compound) in the tree view.
  2. Go to File > Export.
  3. Choose your desired format (such as STL Mesh for 3D printing or STEP with colors for CAD exchange) and save the file.