Assembly Workbench¶

The Assembly workbench (introduced in FreeCAD 1.0) provides a constraint-based system for positioning multiple parts relative to each other and simulating their motion. It is FreeCAD's built-in assembly tool, replacing the need for third-party add-ons for most common assembly tasks.

What the Assembly workbench is for¶

Assembly answers the question: how do these parts fit and move together?

Given a set of individual parts — a shaft, a housing, bearings, bolts — Assembly lets you:

Insert the parts into an assembly container.
Ground one part to fix it in space as the reference.
Add joints (constraints) that define the allowed relative motion between pairs of parts: a revolute joint makes a shaft spin inside its housing; a slider joint makes a piston move along a cylinder bore.
Solve the assembly — FreeCAD moves each part to satisfy all joints simultaneously.
Animate the result — use the Simulation tool to drive a joint through a range of motion and watch the mechanism move.
Explode the assembly for documentation and presentations.
Generate a Bill of Materials listing every component.

Key concepts¶

Assembly object and activation¶

An assembly is an Assembly::AssemblyObject — a container that holds parts and joints. You can have multiple assemblies in one document (sub-assemblies). Only one assembly is active at a time; joints and inserts apply to the active one.

Links, not copies¶

Parts are inserted as links (App::Link) rather than copies. A link references the original part geometry; no second copy of the geometry is stored. Changing the part (e.g. increasing a pad length) automatically updates the assembly. The link carries its own placement (position + orientation) inside the assembly.

Joints¶

A joint is a kinematic constraint between two parts. Each joint defines how many degrees of freedom (DOF) the two parts have relative to each other:

0 DOF (Fixed joint) — no relative motion; the parts are locked together.
1 DOF — one rotation (Revolute) or one translation (Slider).
2 DOF — rotation + translation along the same axis (Cylindrical).
3 DOF — free rotation about a point (Ball).

Adding joints reduces DOF until the assembly is fully constrained (each free part starts with 6 DOF: 3 translations + 3 rotations).

Grounding¶

Every assembly needs at least one grounded part — a part whose position is fixed in the assembly frame. Without a ground, the solver has no reference and all parts float. Typically the base plate, chassis, or frame of a mechanism is grounded.

The solver¶

The Assembly workbench uses an integrated constraint solver. After adding joints, press Solve Assembly to compute positions. The solver reports success (all joints satisfied) or failure (over-constrained, under-constrained, or conflicting joints).

Typical workflow¶

1. Create Assembly          ← Assembly → New Assembly
2. Insert parts             ← Assembly → Insert Component (repeat)
3. Ground one part          ← Assembly → Toggle Grounded
4. Add joints               ← Assembly → Joints menu (repeat)
5. Solve                    ← Assembly → Solve Assembly
6. (Optional) Animate       ← Assembly → Simulation
7. (Optional) Explode       ← Assembly → Exploded View
8. (Optional) BOM           ← Assembly → Bill of Materials

Relationship to other workbenches¶

Workbench	Relationship
Part Design	Bodies created in Part Design are inserted as components.
Part	Part shapes can be inserted as components.
Sketcher	Sketches referenced from parts update assembly positions when the sketch changes.
Spreadsheet	Part dimensions driven by a spreadsheet update the assembly automatically on recompute.
TechDraw	Assembly views and exploded views can be projected into TechDraw drawings.

See the Tools index for a complete reference.