Assembly Constraints

Reference docs for the seventeen assembly mate constraints — what pins one placed component to another in an Assembly document. One page per constraint.

Constraints are not features: they are not in the Add-feature palette, and the workbench feature filter does not apply to them.

Where constraints are offered

Select the geometry, and a constraint is offered in three places: the selection context bar, the Constraints group on the workbench actions toolbar, and the Constraints panel's + dropdown. All three pre-seed the constraint's elements from the selection. A constraint is offered only when the selection could carry it: for the eleven pairing constraints that means two elements on two distinct components, because a pair on one rigid body cannot move anything. Center and Symmetric have their own rules, on their pages.

There is no Fixed constraint. A part is fixed (grounded, never moved by the solve) by its own setting: Fix / Unfix on its row in the components list, the BOM row menu or the selection context bar, the Fixed checkbox in its component dialog, or component_set_fixed. Each is the same one change — the component's isFixed — and one undo step, and a fixed part shows the glyph wherever it is listed. A document saved with a Fixed constraint opens with that part's Fixed setting on instead, in the same place, and says so once.

The Constraints panel has no Cancel and no buffer: a value commits as soon as its field does, and the assembly re-solves.

Automation reaches the same constraints through assembly_constraint_catalogue and assembly_add_constraint.

Walkthroughs

Every page but Symmetric, Gear, Rack and Pinion, Screw, Path, Slot and Cam (new, not yet recorded) has a walkthrough: a captioned recording of that constraint applied to the same two-component assembly — a grounded plate with a bore, and a loose pin — with the control each step presses ringed. Each is generated from a script, not recorded by hand, so it cannot quietly fall behind the product; regenerate them all with ./build.sh docs-videos.

The sixteen constraints

In the order the panel's + dropdown offers them:

• Coincident — COIN. Two elements share a point; anything paired with a planar face has its point put on that plane
• Touch Align — TALN. Seats one element against another — brought together AND made to face each other
• Parallel — PARA. Two direction-bearing elements point the same way. Orientation only: it turns a part, never moves it
• Distance — DIST. Holds a signed gap. Carries a number, and its viewport arrow is draggable
• Angle — ANGL. Holds a turn in degrees. Carries a number, and its viewport arc is draggable
• Concentric — CONC. Two axes on one line — a shaft in a bore, a bolt through a stack. Radii need not match
• Perpendicular — PERP. Two direction-bearing elements at a right angle. Orientation only, and no parameters at all
• Tangent — TANG. Rests a curved face on another so they touch along one line. Faces only
• Center — CNTR. Holds a part midway between two parallel faces of another. Three or four elements
• Symmetric — SYMM. Two like elements mirrored about a planar face, usually of a third component. Three elements
• Gear — GEAR. Turning one gear turns the other by a ratio, the opposite way unless reversed
• Rack and Pinion — RACK. A pinion's turn moves a rack along its travel, and back
• Screw — SCRW. A nut advances along a screw by the pitch per turn
• Path — PATH. A point of one part rides an edge of another — straight, circular or freeform — free along it or held at a set place
• Slot — SLOT. A pin rides the centreline between a slot's two round ends, stopping at either end
• Cam — CAM. A roller, ball or point rides a cam's curved profile, outside it or (flipped) inside

See the Assembly workbench for what all seventeen share: the Constraints panel, the solver and its degrees-of-freedom readout, the viewport graphics, and Auto constraints, which reads an imported assembly's placement back as Concentric, Touch Align and Coincident mates.