Overview#
A joint origin is a coordinate frame (a point plus orientation) that you place on a component to say "this is where I will connect this part". When you later make a joint, you can pick joint origins instead of raw geometry. This gives you precise, repeatable, and edit-proof connection points.
You do not always need them. The Joint command can create a temporary joint origin on the fly by snapping to a vertex, edge midpoint, circle center, and so on. Pre-made joint origins are worth the effort when:
- The connection point is not on existing geometry (the center of a gap, the midpoint between two faces).
- A hole or edge may change during design, and you want the origin to stay at a defined location.
- You will use the same connection point repeatedly (a standard bolt pattern).
- You want a joint to survive geometry edits more robustly than a snap to a face edge.
A joint origin lives inside a component, in the Joint Origins folder in the Browser. It moves with the component.
Where to find it#
- Design workspace > Solid tab > Assemble panel > Joint Origin. Use Command Search (S) and type "joint origin" if you cannot find it.
- The Joint command creates joint origins in the context of a specific joint as you pick snap points; the separate Joint Origin command creates independent ones for more complex locations.
- Edit an existing one by right-clicking it in the Browser under Joint Origins > Edit Joint Origin.
Tip: The Joint command itself is J, and As-built Joint is Shift+J. Autodesk's shortcut list gives no default shortcut for Joint Origin.
Step by step#
Creating a Simple joint origin#
- Activate the component that will own the joint origin (see Components vs Bodies). The origin belongs to the active component.
- Choose Assemble > Joint Origin.
- In the dialog, set Mode to Simple.
- Hover the geometry. Blue snap points appear at vertices, circle/arc centers, edge midpoints, and face centers. Click the point you want.
- Adjust Offset X/Y/Z, Angle, Flip, and Reorient if needed, then click OK.
Creating a Between Two Faces origin#
- Choose Joint Origin and set Mode to Between Two Faces.
- Select Plane 1 and Plane 2. Fusion centers the origin between them.
- Select a Snap point to locate the origin, and use Flip if the axes point the wrong way.
- Click OK.
This is ideal for placing a hinge pin origin in the middle of a slot, or the center of a rail between two walls.
Creating a Two Edge Intersection origin#
- Choose Joint Origin and set Mode to Two Edge Intersection.
- Select Edge 1 and a non-parallel Edge 2. The origin is placed at their extended intersection.
- Adjust the alignment, then click OK.
Use this for corners that are not modeled as vertices, such as the imaginary intersection of two chamfered edges.
Using joint origins in a joint#
- Choose Assemble > Joint.
- For Component 1, click the joint origin icon in the canvas.
- For Component 2, click its joint origin.
- Choose the motion Type and click OK. The components snap together at their origins.
Options reference#
| Option | What it does | Notes/default |
|---|---|---|
| Mode: Simple | Places the origin on a face, edge or point at the Snap you click. | |
| Mode: Between Two Faces | Centers the origin between Plane 1 and Plane 2, then you pick a Snap. | Best with parallel faces. |
| Mode: Two Edge Intersection | Places the origin at the extended intersection of Edge 1 and a non-parallel Edge 2. | |
| Snap | Snap point where the origin is placed. | Hold Ctrl (Command on Mac) over a face to snap to points on it, or over a hole to reach points on its obscured center axis. |
| Offset X/Y/Z | Offsets the joint origin along X, Y or Z. | Use for clearance or mid-height of a hole. |
| Angle | Rotates the reference coordinate system of the origin. | |
| Flip | Flips the origin to align components. | |
| Reorient (Z Axis / X Axis) | Select a face or edge to reorient the Z axis and the X axis of the origin. | |
| Name | Name shown in Browser. | Rename to something meaningful, like "JO_pin_center" (general advice). |
How joint origins relate to joints#
A joint is essentially "origin on component 1 meets origin on component 2, with a specified freedom of motion". Each origin icon is a coordinate system: its planar face is the XY plane, the red axis is +X, the green axis is +Y, the white side of the icon is +Z and the orange side is -Z. Understanding the frame matters:
- Z axis is the principal direction: the rotation axis of a revolute joint, the slide direction of a slider, the normal of a planar joint.
- X and Y axes define the zero position for angle and the reference direction for offsets.
Note: not confirmed in Autodesk's documentation: which origin axis defines the zero reference for slider travel and revolute angle; check the Motion tab preview.
If a joint behaves strangely, show the origins with Display Settings > Object Visibility > Joint Origins (or Joint Origin Axes for just the axes) in the Navigation bar and check the axes.
Joint origins versus snapping on the fly#
| Aspect | Pre-made joint origin | On-the-fly snap |
|---|---|---|
| Setup time | Extra step | None |
| Reuse | Yes, any number of joints | One joint |
| Robustness to edits | High if the origin references stable geometry | Depends on the snapped geometry |
| Placement not on geometry | Yes (Between Two Faces, offsets) | Only via offset in the joint dialog |
| Visible in Browser | Yes | Hidden inside the joint |
Tips and pitfalls#
Tip: Create joint origins in the part's own coordinates. For a standalone part file, make the joint origins in the part and they come along when the part is inserted into any assembly.
Tip: Name your origins by function: "JO_hinge", "JO_mount_hole_A". When you have a dozen, the default "Joint Origin1..12" is useless.
Warning: A joint origin references geometry. If you delete or fundamentally change that geometry (for example, delete the hole it snapped to), the origin can become unresolved and the joint using it fails. Fix by editing the origin to snap to something stable.
Warning: A joint origin created while the wrong component is active belongs to that wrong component. Joints that use it will connect the wrong part. Always check the active component.
Tip: For hardware like screws, put the joint origin at the center of the head underside, aligned with the screw axis. Then one joint origin on the screw plus one at each hole gives repeatable placement.
Tip: A joint origin on a pinned component is stationary; the other component moves to meet it.
Warning: Large offset values in Z can place the joint origin outside the part. Fusion allows this, but it is easy to lose track of and confusing to debug.
Worked example: a joint origin for a mounting bolt pattern#
A bracket has four 6.5 mm holes in a 40 x 30 mm rectangle. You want to mount it on a plate by the center of the pattern, not by one hole.
- Activate the bracket component (not the assembly).
- Start Joint Origin and choose Between Two Faces or, if the pattern has no faces to bracket it, use Simple on a sketch point you placed at the rectangle center (20 mm, 15 mm from the corner hole).
- Set the origin Z so it points out of the bracket's mounting face; if the preview points inward, use the flip.
- Name it "MOUNT_CENTER".
- Repeat on the plate for the matching center. Now a single Rigid joint between MOUNT_CENTER on the bracket and the plate origin aligns both patterns, and you can change the hole spacing from 40 to 50 mm without redoing the joint, as long as the sketch point stays at the center.
If you had snapped to one hole edge instead, changing the spacing would move the joint with the hole and misalign the pattern.
Choosing an origin for the right motion#
| Mechanism | Where the origin goes | Axis |
|---|---|---|
| Hinge with a pin | Center of the pin or bore edge on each part | Z along the pin |
| Sliding drawer | Centerline between the two guide faces | Z or X along travel, depending on the joint type |
| Screw in a threaded hole | Hole center at the surface | Z along the screw |
| Wheel on an axle | Bore center at mid-width | Z along the axle |
For the wheel, use Between Two Faces on the hub faces so the origin sits at mid-width. A snap to just one face puts the origin 6 mm off center on a 12 mm wide hub, and a rigid joint to the axle then shifts the wheel sideways by that amount.
Failure modes and fixes#
| Symptom | Cause | Fix |
|---|---|---|
| Part flips 180 degrees on joining | The two origin Z directions point the same way | Use Flip in the joint, or flip the origin. |
| Part lands offset by half its thickness | Origin placed on one face rather than the midplane | Recreate with Between Two Faces. |
| The origin vanishes after a model edit | The referenced geometry was deleted or re-created | Define the origin from sketch points or construction geometry that is stable. |
| Joint origin not selectable in the Joint command | Its component is hidden, or origin visibility is off | Turn on Object Visibility > Joint Origins and make sure the component is visible. |
| Two edge intersection fails | Edges do not intersect in 3D, even if they appear to in the view | Extend one edge with a construction line or use Simple. |
Naming and organizing#
Treat joint origins as the interface of the part. Give them names that describe the function ("HINGE_A", "MOUNT_TOP", "BEARING_SEAT") and keep them in the part file, not only in the assembly. When a part is reused, anyone can attach it with a single joint. A part with eight origins, each named, is far easier to maintain than one that needs a snap hunt every time.
Stable references#
Joint origins that follow a face break when that face is re-created (for example when you reorder timeline features). The most stable references, in order, are:
- Sketch points and construction geometry tied to origin planes.
- Origin planes and axes.
- Edges and faces created early in the timeline.
- Edges and faces created late, especially fillet or chamfer edges.
Prefer the first two for anything that other parts depend on.
Practice exercise#
- Model a plate with a 10 mm slot and a pin (separate components, "Plate" and "Pin").
- In Plate, create a Between Two Faces joint origin using the two long side faces of the slot as Plane 1 and Plane 2, with the Snap at slot mid-length. Name it "JO_slot".
- In Pin, create a Simple joint origin at the center of the pin's bottom face and name it "JO_pin_base".
- Pin the Plate. Use the Joint command, click JO_pin_base for Component 1 and JO_slot for Component 2. Choose a Slider joint along the slot.
- Drag the pin and confirm it travels along the slot.
Expected result: the pin sits centered in the slot and slides along its axis only.
Stretch challenge#
Build a knob and a panel. Create three named joint origins on the knob: BORE_TOP, BORE_MID, BORE_BOTTOM at 0, 6 and 12 mm along a 12 mm bore. Join the knob to a 6 mm shaft using each in turn and note how the knob sits relative to the panel (0, 6 or 12 mm of insertion). Expected result: the knob moves 6 mm each time you swap origins, with no manual offset. Then change the bore depth to 16 mm; confirm that BORE_BOTTOM, if tied to the bore floor, follows to 16 mm while the others remain.
Related#
- Joints
- As-Built Joints
- Joint Limits and Motion Links
- Components vs Bodies