Open SolidCraft above to try it in your browser, or download it for your desktop. This guide covers how assemblies work in SolidCraft: components, joints, motion and checks. Everything here comes from SolidCraft's official documentation (version v0.21.0, released 24 October 2026), linked at the bottom.
New to the app? Start with the SolidCraft tutorial first.
How a SolidCraft assembly is built
There is no separate assembly file type. A design is a tree of components, and each component has its own origin, bodies, sketches and timeline entries.
- New Component adds a component. Create Components from Bodies turns bodies you already modelled into components.
- The active component (the radio button in the browser) receives new sketches and features. Others are drawn faded.
- A component is placed by its occurrences. Paste makes another instance of the same component. Paste New makes an independent copy.
Place and ground your parts
The first part placed in the design is grounded automatically: it can't move. Parts made after it start free. You can ground or unground any part from the browser's right-click menu, and you can ground as many parts as you like, or none.
To move a part, drag it with the left mouse button. It follows the pointer and stays where you let go, as one undo step. Escape during the drag puts it back. You can also use the move triad, then Capture Position to keep the move or Revert to undo it.
Connect parts with joints
Press J for Joint. A joint connects two components by joint origins that snap to faces, edges, circles and vertices. SolidCraft has seven joint types:
| Joint | What it allows |
|---|---|
| Rigid | No motion |
| Revolute | Turning about one axis |
| Slider | Sliding along one axis |
| Cylindrical | Turning and sliding on one axis |
| Pin-slot | Turning plus sliding along a slot |
| Planar | Moving in a plane |
| Ball | Turning about a point |
Each joint takes offsets, flip and limits. Other options:
- As-built Joint keeps the parts where they are now.
- Rigid Group locks several components together.
- Relations fix only part of a placement, one rule at a time: parallel, perpendicular, angle, point on plane, point on line and line on plane. Several relations between the same two parts add up.
- Offsets, angles and values can be expressions of your parameters, such as
gap + 2. Change the parameter and the part moves with it.
Common snag: both picks of a joint must be on different components. A STEP file with several parts often imports as bodies of one component. The Joint dialog spots this and offers Create Components from Bodies. See SolidCraft STEP files for importing.
Make it move
- Drive Joints moves a joint through its values. If something stops it, the dialog says why: a loop that can't close further, a limit, or a contact set.
- Motion Link couples two joints, and links can be chained up to 64 deep.
- Gear, Rack and Pinion and Screw on the ASSEMBLE panel take their ratio from the parts: pick the gear faces, or type radii or tooth counts.
- Cam makes a follower ride a cam profile. The SolidCraft CAM page explains cam joints in detail.
- Closed loops such as a four-bar linkage or slider-crank stay closed while you drive them, and stay on the branch they started on.
- Dragging a jointed part moves it only as far as its joints allow.
A chain of joints that isn't connected to anything grounded never moves. SolidCraft tells you which part is unconnected. Ground one part of the chain, or join it to a grounded part.
Motion studies, traces and animation
Motion Study keys joint values along a timeline. Its dialog can:
- plot a joint's value, velocity or acceleration, or a picked point's distance, speed and acceleration;
- Check collisions across the whole study and list the colliding parts and steps;
- Export Animation… as an animated GIF. Scripts and the CLI can also write PNG frames for a video tool.
Motion Trace draws the path a point takes as the mechanism moves, such as a four-bar's coupler curve, and keeps it as a 3D sketch spline you can sweep along. The official Chebyshev linkage demo shows the full workflow.
Check fit: interference and clearance
Interference shows overlapping volumes in red, lists pairs closer than your Clearance, and each body's nearest neighbour. Distances are measured on exact faces and edges. Mesh bodies from STL, 3MF and OBJ imports are not checked and are listed as unchecked, so an empty result never hides them.
Multi-file assemblies
Insert Design adds a component linked to another saved .solidcraft design, so each part can live in its own file. The bodies are kept in the assembly, so it opens even without the part file. Update Links reloads changed parts, Break Link forgets the file, and Relink Source fixes a part that moved. Extract to File turns an existing component into its own design.
Bill of materials and export
Give each component a part number, description and revision, then open Bill of Materials on the INSPECT panel. It lists parts flat or top-level, groups them by part number and exports to CSV or JSON. Standard parts such as ISO 4762 screws get part numbers automatically. Right-click a component and choose Properties for mass, volume and centre of mass.
STEP export writes the component tree as an assembly. Robots go one step further with SolidCraft URDF export.
Scripts and AI agents
Every step above has a command: joint.create, joint.drive, inspect.clearance, assembly.bom and more. You can run them from the SolidCraft CLI or let an AI assistant build the assembly through the SolidCraft MCP server.
Ready to build one? Get the app from the SolidCraft download page.