FreeCAD Part vs Part Design: What Is the Difference?

FreeCAD offers two primary environments for creating 3D solid models: the Part workbench and the Part Design workbench. While both tools generate 3D geometry, they rely on fundamentally different modeling philosophies, workflows, and underlying structures. The Part workbench uses a Constructive Solid Geometry (CSG) approach based on independent shapes and Boolean operations, whereas the Part Design workbench uses a modern, feature-based parametric workflow centered on sketches and single contiguous bodies.

Modeling Philosophy: CSG vs. Feature-Based

Part Workbench (Constructive Solid Geometry)

The Part workbench follows a traditional Constructive Solid Geometry (CSG) methodology. You create shapes by combining geometric primitives—such as cubes, cylinders, and spheres—or by extruding 2D shapes. Complex objects are created by applying Boolean operations (unions, cuts, intersections) between these individual shapes.

In the Part workbench:

• Each object or primitive is an independent entity in the model tree.
• Solids can exist anywhere in 3D space without needing to be connected.
• The design tree represents a hierarchy of Boolean operations rather than a strict chronological timeline.

Part Design Workbench (Feature-Based Parametric)

The Part Design workbench uses a modern feature-based approach common in industrial CAD software. Models are created sequentially within an explicit container called a Body.

In the Part Design workbench:

• A single Body must always represent a single contiguous solid; disconnected geometry within the same body is generally not permitted.
• The workflow relies heavily on 2D sketches mapped to planes or existing faces, which are then transformed into 3D features via tools like Pad, Pocket, Revolve, or Loft.
• The model tree represents a strict linear history where each feature builds upon the previous one.

Core Workflow Differences

Strengths and Use Cases

When to Use the Part Workbench

• Imported Geometry: Modifying or repairing imported STEP, IGES, or BREP files that lack parametric feature histories.
• Direct Boolean Operations: Quickly combining, subtracting, or intersecting multiple complex shapes without sketch dependencies.
• Multi-Solid Modeling: Working with models containing multiple disjointed parts in a single document without using an assembly workbench.
• Low Parametric Dependency: Simple models that do not require heavily constrained dimensions or iterative design revisions.

When to Use the Part Design Workbench

• Mechanical Components: Designing parts for 3D printing, CNC machining, or injection molding that require exact parametric constraints.
• Sketch-Driven Design: Parts that rely heavily on fully constrained 2D profiles with dimensions, symmetries, and geometric constraints.
• Sequential Features: Designs requiring standard mechanical features such as countersunk holes, fillets, chamfers, and patterns (circular or linear).
• Iterative Design: Projects where changing a single dimension in an early sketch needs to automatically and predictably update the rest of the model.

Combining Both Workbenches

While the two workbenches serve distinct functions, they can be used together in a single project. A common approach is to design individual components inside separate Part Design Bodies, then switch to the Part workbench to perform global Boolean operations between those finished bodies. However, referencing features from one workbench inside the active tree of the other should be done with caution to avoid topological naming issues and broken model dependencies.