Manage Active and Inactive Bodies in FreeCAD

Working with multiple bodies in FreeCAD's PartDesign workbench requires a solid understanding of the active body workflow. In FreeCAD, new features like sketches, pads, and pockets are strictly assigned to whichever body is currently set as "active." This guide explains how to toggle active and inactive bodies, manage their visibility, reference geometry across bodies safely, and avoid common modeling errors in multi-body projects.

Understanding the Active Body Concept

In the PartDesign workbench, a Body is a container that holds a single, contiguous solid constructed through a sequential feature tree. FreeCAD enforces a single-active-body rule: only one body can be active at any given time.

When a body is active:

  • Its label appears in bold text within the Tree View.
  • Any new sketches, datum tools, or additive/subtractive features are automatically placed inside this body.
  • Inactive bodies remain static background objects, serving as visual references or components for assemblies and boolean operations.

How to Activate a Body

To direct your modeling operations into a specific body, make it active using either of these methods:

  1. Double-Click: Double-click the target Body in the Tree View. Its text will turn bold.
  2. Context Menu: Right-click the Body in the Tree View and select Toggle active body.

Activating a body automatically deactivates the previously active body.

How to Deactivate a Body

If you want no body to be active (for example, to inspect the model or prevent accidental modifications):

  • Right-click the currently active (bold) body in the Tree View and select Toggle active body.
  • The bold styling will disappear, indicating that no body is receiving new features.

Managing Visibility of Inactive Bodies

Body activity and body visibility are separate properties:

  • Toggle Visibility: Select any body (active or inactive) in the Tree View and press the Spacebar to hide or show it.
  • Ghosting/Transparency: If an inactive body obstructs your view while working on the active body, select the inactive body, go to the View tab in the Property panel, and adjust its Transparency (e.g., 50–70%) instead of hiding it entirely.

Referencing Inactive Bodies Safely

Modeling features in an active body that depend on an inactive body requires caution to avoid cyclic dependencies and broken links:

  • Use ShapeBinder or SubShapeBinder: Never map a sketch directly to the face of an inactive body. Instead, activate your target body, select the face or edge from the inactive body, and click the SubShapeBinder tool. This creates a stable internal reference inside the active body that you can safely constrain sketches to.
  • Boolean Operations: To combine, cut, or intersect bodies, make the primary body active, select the Boolean operation tool from PartDesign, and add the inactive bodies into the operation list.

Best Practices for Multi-Body Projects

  • Name Bodies Immediately: Default names like Body, Body001, and Body002 quickly lead to confusion. Right-click and choose Rename (or press F2) to give each body a descriptive name based on its function.
  • Check the Bold Label Before Modeling: Always glance at the Tree View before creating a sketch to ensure the bold body is the one you intend to modify.
  • Keep Bodies Contiguous: If an additive or subtractive feature creates separated, disjoint solids inside the active body, FreeCAD will produce errors. Use separate bodies for physically separate parts.