Components and joints

A design is a tree of components. New Component (component.create) adds one, and Create Components from Bodies (component.from_bodies) turns bodies into components. Each component has its own origin, bodies, sketches and timeline entries. The active component (the radio button in the browser) receives new sketches and features; the others are drawn faded.

A component is placed by its occurrences. Paste creates another instance of the same component, and Paste New creates an independent copy. Move an occurrence with the move triad, then Capture Position to keep it or Revert to put it back. Polykrom asks before the next command if a move wasn’t captured. Ground fixes an occurrence in place.

Paste New copies nested component definitions, sketches, feature histories and generated dimension parameters. Repeated child instances remain shared within the new copy. Materials, appearances and wholly internal joints/motion records receive copied references. Design-wide user parameters remain shared; retained external links and omitted cross-boundary motion records are reported. Unsupported destructive links refuse the entire copy. See individual-instance and copy details.

Joints (joint.create, J) connect two components by joint origins that snap to faces, edges, circles and vertices: rigid, revolute, slider, cylindrical, pin-slot, planar and ball, with offsets, flip and limits. As-built Joint keeps the current position, Rigid Group locks components together, Drive Joints moves a joint through its values, and Motion Link couples two joints. Links can be chained (one joint drives a second, which drives a third), and a value is carried through a chain of up to 64 links in whatever order they were made. Contact sets stop motion where bodies would pass through each other, Motion Study keys joint values along a timeline, and Interference shows overlapping volumes in red, lists the pairs closer than its Clearance and each body’s nearest neighbour.

A joint origin on a face or a hole keeps the turn it had when it was picked: when the face tilts (a bend angle or a rotation changing with a parameter) the part on it tilts with the face but doesn’t spin about it.

A joint origin can also sit on an edge of a flat face ("edge": [x, y, z]): at the edge’s middle, pointing out of the face with its y into it, or with "corner": [x, y, z] at the corner near that point, its x and y running along the two edges into the face. The edge, the face and the corner are found again by name, so a bracket set 40 mm in from a panel’s corner (a planar joint with values [40, 40, 0]) stays 40 mm in from that corner when the panel changes size.

A joint’s offset, angle and values can be typed as expressions over the design’s parameters ("offset": "gap + 2", "values": ["travel"]). The joint keeps them and works them out again whenever the design changes, so a part seated gap above a panel moves with gap. Renaming a parameter carries into the joints that use it, and deleting one they use is refused. If an expression stops working out (say a parameter becomes an angle), the joint is left out of the solve and joint.solve gives the reason, instead of placing the part from old numbers. Typing a plain number, or driving the value, drops that expression.

Relations are joints that tie only part of a placement, so a part is placed the way a designer describes it, one relation at a time: parallel (z along z, free to move and turn about it), perpendicular and angle (z square to z, or at the joint’s angle from mated), point_on_plane (a point on a face’s plane, offset off it), point_on_line (a point on an axis) and line_on_plane (an axis on a face’s plane: a cylinder’s radius as offset lays it tangent). A relation is made where the parts are: B moves no further than the relation needs. Several relations between the same two parts add up; the solver meets them together, each one’s degrees of freedom come off what is left, and one that can’t be met is reported, not forced:

{"command": "joint.create", "params": {"type": "parallel", "a": "Panel top", "b": "Bracket bottom"}}
{"command": "joint.create", "params": {"type": "point_on_plane", "a": "Panel top", "b": "Bracket corner"}}
{"command": "joint.create", "params": {"type": "parallel", "a": "Panel front", "b": "Bracket face", "flip": true}}
{"command": "joint.create", "params": {"type": "point_on_plane", "a": "Panel front", "b": "Bracket corner", "offset": -40}}
{"command": "joint.create", "params": {"type": "point_on_plane", "a": "Panel end", "b": "Bracket corner", "offset": -40}}

leaves the bracket flat on the panel, square to its front, its corner 40 mm in from the front and the end, wherever the panel’s size takes them. Coincident faces are a planar joint, a distance between faces is planar with an offset, concentric is cylindrical and two points that meet are ball.

The check behind it, inspect.clearance, does all of that in one call for any number of bodies, which suits scripts and agents checking a whole assembly:

{"command": "inspect.clearance", "params": {"clearance": 1, "nearest": 2, "skip_within": "component"}}

It returns overlaps (pairs sharing at least min_volume, 0.01 mm³ by default, with the shared volume, area, box and centre), near (pairs closer than clearance, with the distance and the two nearest points; a contact sharing less than min_volume is listed here at 0 with its overlap_mm3), nearest (each body’s nearest closest bodies) and unchecked (pairs whose overlap could not be worked out, with the reason). against limits the check to pairs with one body in bodies and the other in against, and skip_within leaves out pairs inside one occurrence ("occurrence") or one placed component, its subcomponents included ("component"): the parts of a bought component that touch by design. Distances are measured on the exact faces and edges; the meshes only rule out pairs that are too far apart, and the pairs left are checked in parallel. inspect.interference remains for the overlaps alone: it clears pairs whose meshes stay apart without intersecting them, intersects the rest in parallel, and returns after budget_s seconds (default 240) at most, listing the pairs it had no time for as not checked.

Mesh bodies (STL, 3MF and OBJ imports) are not checked by either command: each is listed in unchecked as {a: name, b: null, reason: "mesh body: not checked"}, so count: 0 or an empty overlaps is not mistaken for “no overlap” when a mesh body was in the design.

Gear, Rack and Pinion and Screw (on the ASSEMBLE panel) are motion links whose ratio comes from the parts rather than a typed number:

• Gear (joint.gear {a, b, ra, rb}) couples two joints that turn. Joint 2 turns ra/rb as far as joint 1, the other way round; Internal gear (one of them is a ring gear) turns both the same way. Pick the round face of each gear, such as its pitch cylinder, or type the radii. Tooth counts work as well as radii, since only their proportion counts. Picking a gear’s face also chooses the joint that gear turns on.
• Rack and Pinion (joint.rack_pinion {a, b, radius}) couples a joint that turns with one that slides: the rack travels the pinion’s pitch radius times its turn in radians (r·θ). Either joint may drive the other. In joint.list the ratio is given per degree, as for any link between an angle and a distance.
• Screw (joint.screw {joint, pitch}, or {a, b, pitch} for a revolute joint and a slider) advances pitch per turn. A cylindrical joint is a screw on its own: its turn drives its travel. The thread is right-handed; Reverse makes it left-handed.

A radius or pitch may be an expression of the design’s parameters, and a picked face is found again whenever the design changes. Change the parameter or the gear’s diameter, and the ratio follows. The new link leaves the driven joint where it is, so teeth modelled in mesh stay in mesh. Reverse turns the driven joint the other way, for joints whose axes point opposite ways. Redefining a link (link: i, such as turning it the other way with Reverse) also leaves the driven joint where it is, so the gears stay in mesh at the pose they are in. These couplings are motion links, so they work in closed loops, with contact sets and in motion studies: a rack can push the piston of a slider-crank, or a pinion can steer through a rack and its tie rods. Drive the joint that drives the coupling (joint 1, the pinion, or the screw’s turn), not the driven one. A joint follows one link at most, and a coupling that would drive its own driver is refused. joint.list lists each coupling’s definition under links with an error when it can’t be worked out (the picked face is gone); the link then keeps its last ratio.

Cam (joint.cam {a, b, profile}, on the ASSEMBLE panel) makes a follower ride a cam. The cam turns on a revolute joint (a); the follower is a slider (b, a translating follower such as a valve tappet) or a revolute joint (b, an oscillating follower such as a rocker arm). The profile is the cam’s outline in a plane square to its axis: a closed profile of a sketch in the cam’s component, or the cam’s edges picked on its body (one click on an edge takes the closed loop it is on in that plane). The follower is:

• a Knife edge: a point on the cam;
• a Roller of a radius, typed or taken from the roller’s round face (picking that face also says where the roller is);
• a Flat face square to a slider’s line, such as a bucket tappet.

A translating follower’s line runs along its slider’s axis, through its Tip when one is picked (its knife’s point or its roller’s centre), so a follower offset from the cam’s axis rides the right flank. An oscillating follower needs its tip, or its roller’s face, to know its arm. The follower rides the cam from the side it is on (Other side takes the other one). The follower’s travel over a turn of the cam is worked out from the profile and kept with the link, one value a degree with a smooth curve between them that never overshoots its samples. It is worked out again whenever the design changes: change the cam’s sketch, a parameter or the roller, and the follower follows. Like the gears, the new link leaves the follower where it is (model it touching the cam), and the cam is a motion link: it drives in Drive Joints, plays in motion studies, works in closed loops (a tappet can be the piston of a slider-crank) and stops at contact sets. The profile may also be on the grounded part, with the follower’s guide on a turret that the cam joint turns. joint.list gives a cam’s link lift (the follower’s lowest and highest values and its rise) instead of a ratio. A profile that is not closed, a line or an arm that misses the cam somewhere, a follower that would jump, and axes that are not square or parallel are refused.

A joint moves one component against another, so its two picks must be on different components. A STEP file with several parts often comes in as bodies of one component, and picks on two of those bodies make no joint. The Joint and As-built Joint dialogs say so under the picks and offer Create Components from Bodies: each picked body gets a component of its own and stays where it is, the picks are kept, and the joint previews. joint.create refuses such origins with the same advice.

Joints may close a loop, as in a four-bar linkage or a slider-crank. When one joint of the loop is driven, the other joints in the loop follow so that every joint still meets, and the mechanism stays in the assembly mode it started in (an open four-bar does not flip to the crossed one). If the motion would take a loop past the point where it can still close, for example driving a rocker beyond its swing, the motion stops at the last position where the loop closes, and the drive reports stopped_by_loop. A loop that cannot close at all is listed under conflicts and nothing in it moves. joint.list reports how many degrees of freedom each part still has with its loops closed: the moving parts of a four-bar have one between them, and a loop locked by a rigid joint has none. A joint a motion link drives adds no freedom of its own: two meshed gears on a fixed housing have one between them, each turning with the driving gear. The Drive Joints dialog says when a drive stops short and why. While it previews, a row under the values gives the value the joint reached and the reason (the loop that can’t close further, or the two parts a contact set keeps apart), and after OK the status line repeats it. The value box keeps what you typed. The dialog opens on the joint picked in the browser, or on the first joint that moves when none is picked.

Drag a part that joints place and it moves as far as its joints allow: the point you grabbed follows the pointer in the plane through it that faces the view, the joints on the part’s chain take the values that bring it nearest, within their limits, through motion links, and with closed loops kept closed, and a four-bar’s rocker stops at the end of its swing. The whole drag is one undo step. A grounded part, or one no joint places, is not moved; a drag on it draws a selection box as before. Each frame runs joint.reach, which scripts and agents use directly to put a part’s point somewhere: joint.reach {occurrence, point} moves the joints on its chain from where they are to the nearest pose (the arm keeps its elbow up or down, and a linkage stays on its branch). at picks the part’s point (the centre of its bodies by default), z with axis also turns one of its axes, and joints names the only joints to move (the other joints of a closed loop they are in follow). The answer says whether it reached the point and how close it got (error_mm, error_deg), and when it falls short, the limits it rests on (stopped_by_limit) or the loop that stopped it (stopped_by_loop). Contact sets are not checked by a reach; drive the joints for that.

The solver places what it reaches from the root and from grounded components. A chain of joints that is joined to nothing grounded is never placed, so driving one of its joints moves nothing. The drive says so: joint.drive answers moved: false with a reason and the unconnected part (“Pedestal:1 is not connected to anything grounded”), the Drive Joints dialog shows the same row, motion.play lists such joints under unmoved, and joint.list names every such chain under floating. Ground a part of the chain, or join it to a grounded part (a rigid as-built joint keeps it where it is), and it moves.

joint.drive answers the joint’s values as joint.list gives them, in degrees and millimetres with their units and limits, and moved says whether any part moved. A joint’s origins are mated by default: B’s z axis is turned against A’s, as two faces meet. flip: true lines them up instead, so two origins given at one point with the same z stay as they are. Without an angle, a new joint (other than a relation, which starts where its parts are) takes no turn or a half turn about its axis, whichever turns B less: two faces that already meet, a plate under a panel, stay as they are instead of B spinning about their shared normal. For scripts that drive many steps, quiet: true leaves the per-part degrees of freedom out of joint answers, and motion.play with quiet: true gives the poses of only the parts that moved.

Motion Trace (motion.trace, on the ASSEMBLE panel) draws the path a point of a part takes while a joint is driven or a motion study plays, such as the coupler curve of a four-bar. Pick the point on the part (a face centre, a circle centre, an edge midpoint or a vertex), then either a joint with the values to drive it from and to (a turn of the joint from where it is, at first) or a motion study. The path previews in the viewport as the mechanism would move: closed loops follow, and the path ends where a loop can no longer close or a contact set stops the motion, which the dialog says under the values. OK keeps the path as a 3D sketch spline in a new sketch of the root component (Motion Trace1, …), where no joint moves it, and it can serve as a sweep or pipe path. It is a fixed curve: it does not follow later changes to the mechanism. A path that comes back to where it started is kept as a closed, smooth spline. motion.trace {occurrence, point, joint, from, to, index?, samples?} (or {occurrence, point, study, samples?}) answers the world points without changing the design, and motion.trace.keep with the same parameters (and name?) keeps them. A trace takes 2 to 500 samples: 100 by default for a joint, one per step for a study.

Export Animation… in the Motion Study dialog saves the study as an animated GIF, drawn from the viewport’s camera as the study plays (the keys in the dialog count, even before OK). motion.export_animation does the same for scripts, the CLI and agents, without a window: give a study, or a joint with from and to (and index?) to animate a drive, and a path. A path ending in .gif gets an animated GIF that loops; any other path is a folder that gets the frames as frame-0001.png, frame-0002.png, and so on (made if missing; frames of a longer earlier export there are removed), for a video tool. The web app writes GIFs only. samples is the number of frames (one per step for a study by default, 100 for a joint), width and height their size in pixels (800 × 500 by default, at most 4096 a side), and fps the GIF’s speed (20 by default); grid: false and axes: false leave out the ground grid and the origin’s axes. camera takes the reply of the control channel’s ui.camera (or any of its fields; the rest come from the view view.apply chose, or the home view framing the model). The frames are drawn by the same renderer as solidcraft-cli snapshot, on a copy of the design, which is not changed. A GIF keeps one palette for all its frames, so colours don’t flicker, and stores only what changed from one frame to the next. Frames are capped: at most 1000, and a GIF holds at most 2^26 pixels of frames (about 160 frames of 800 × 500).

Motion analysis. The Motion Study dialog’s Study box opens a saved study to edit, and by its timeline the dialog charts what the study does. Plot picks a moving joint value (a joint picked in the Browser is picked here too), or Picked point once a point is picked in the dialog’s Point box, and Quantity whether to show its value, velocity or acceleration; the chart runs over the study’s steps with a cursor at the step shown, and a click or a drag on it moves to that step. Values are in degrees and millimetres; rates are per step, or per second once Duration says how many seconds the whole study takes. A picked point charts its distance from where it starts, its speed and the size of its acceleration. Check collisions plays the study and lists the pairs of parts that pass through each other, with the steps where they do (a click on one shows the first of them); those steps are shaded on the chart. It checks the parts picked in Components (against the ones picked in Against, when there are any), else every component, or the pairs of the design’s contact sets (a choice beside the button once it has any).

motion.plot {study, joints?, occurrence?, point?, samples?, duration?} answers the same numbers: for each joint value its value, velocity and acceleration per sample (with their units), and for a point its position, velocity and acceleration vectors, speed and acceleration_norm. The study plays as motion.play places it (closed loops follow, contact sets stop it), each sample from the one before, on a copy: the design is not changed. Velocities and accelerations are finite differences between samples, central inside and one-sided at the ends, so they are as smooth as the samples are dense (up to 1000, one per step by default). Angles are unwrapped, so a joint that turns on past half a turn keeps counting. motion.interference {study, occurrences?, against?, contact_sets?, samples?} answers each colliding pair with its first_step, last_step, the steps ranges where they overlap, how far into each other (depth_mm, the most at deepest_step) and their shared volume_mm3 there (null when it is not cheap to work out). It plays the study as motion.play does, but contact sets don’t stop it, and parts are tested at the samples only: a part that passes right through another between two samples is missed. Parts are told apart by occurrence, as contact sets tell them apart: an occurrence inside a sub-assembly placed twice is one part, so its two copies are not checked against each other. A check takes at most 256 bodies; on a large design, list the occurrences to check (an arm, with against the parts it must miss). When the work runs out it says truncated and the step it checked_to. joint.sweep {joint, from, to, index?, step?, refine?, occurrences?, against?, contact_sets?, report_gaps?, apply?} drives one joint value from from toward to and answers how far it gets before parts touch: stopped_at (the last value clear of contact), stopped_by (the two parts and the point at which they touch, or "loop" where a closed loop can no longer close, or "limit"), and with report_gaps the nearest gap at every sample and the nearest each part came to another (min_gap). The samples are fine enough that no part passes through another between two (or step apart), and the first contact is bisected until no part moves more than refine (0.01 mm by default) across it. Gaps are distances between the parts’ tessellations (gap_method: "mesh"): exact for flat faces, within gap_tolerance_mm for curved ones. Pairs already touching at from, such as parts joined face to face or a door resting on its frame, are listed in touching_at_start and stop the sweep only once they pass into each other, deeper than they start. The sweep runs on a copy (closed loops follow, contact sets don’t stop it) and leaves the design as it was unless apply is true.

Insert Design (component.insert_design {path, translate?}, on the ASSEMBLE panel and in the File menu) adds a component linked to another saved design, so each part can live in its own document. A STEP or mesh file picked there is inserted as Insert STEP or Insert Mesh would. The part’s solid bodies come in as they sit in that design, and they are kept in the assembly, so it opens even without the part file. The link is stored relative to the assembly’s folder once the assembly is saved. After the part file changes, Update Links (component.update_links) reads it again. Break Link (component.break_link) keeps the bodies and forgets the file, and component.links lists the links and whether their files are found. A linked component holds the part’s bodies only: its timeline, parameters and sheet-metal data (flat pattern, bend table) stay in the part’s own design.

If a source file moves or is renamed, right-click its linked component or occurrence in the Browser and choose Relink Source (All Instances)…. Choose the saved .solidcraft design to use. Relinking updates that component’s stored path and solid bodies for all its instances, keeping their identities and placements. Cancelling or choosing a missing, invalid, empty or self-referencing design leaves the assembly unchanged. The operation is one undo step and the new path is saved relative to the assembly when possible.

Scripts use component.relink {component, path}. The reply includes previous_path, path, warnings, joint_errors and joint_conflicts. Changed geometry can invalidate a joint’s face reference: relinking reports those joints in the reply and UI status/message history; repair the joint or undo the relink. Relink does not repair or verify the intended meaning of existing joints. When linked geometry changes and the component has joints, a reminder to check those joints is also shown even if the solver reports no error: a successful solve does not prove that a joint still describes the intended connection.

STEP export writes the component tree as an assembly.

Right-click a component in the Browser and choose Properties to inspect material-aware mass, volume, surface area, centre of mass and world bounds. Descendants and repeated instances contribute to assembly totals; pending moves are included. A component uses its first placement; occurrence.properties selects a specific instance. Root Properties measures the complete assembly. Volumes are summed, including overlapping bodies, rather than measuring their union. The same workflow is available through component.properties and occurrence.properties; see placement and measurement details.

Part properties and the bill of materials

A component definition carries its own part properties: a part number, a description and a revision, other tools’ data under a reverse-DNS key (the same rules as the design’s own properties), and free text properties such as a material grade or a finish. Every occurrence of the component shares them, Paste New copies them, and they are saved with the component. component.metadata {component} reads them and component.metadata.set {component, part_number?, description?, revision?, values?, properties?} changes them in one undo step (an empty value removes a field). The root component is the design itself: its properties are document.metadata’s. Standard parts (parts.insert) get a part number from their standard and size (ISO 4762 M6x20, or a bearing’s designation) and a description; Change Part Size renumbers them, keeping a field you changed yourself.

Bill of Materials (assembly.bom, on the INSPECT panel) counts the placed components:

• levels: "flat" (the default) lists the parts at any depth, each counted through its subassemblies: a part placed once in a subassembly that is placed twice counts 2. A subassembly is listed through its parts, unless it has bodies of its own.
• levels: "top" lists the direct children, a subassembly as one row.
• group_by: ["part_number"] (the default) puts definitions with the same part number in one row; a definition without a part number gets a row of its own. ["definition"] gives every definition its own row.
• group_children: true keeps what is placed inside a part with a part number in that part’s row: a bolt with a washer and a nut placed inside it is one row, the washer and the nut listed under it as children (items 1.1, 1.2…, with each per bolt and count in all) instead of rows of their own. Bolts with different contents (one with a nut, one without) are different rows. total_occurrences counts the children too, so it is the same either way.
• component lists one subassembly’s parts instead of the design’s.

Rows are sorted by part number (rows without one come last) and hold item, part_number, description, revision, count, definition (the component names), components (their ids) and properties, with total_occurrences beside them. path writes them to a .csv file (the columns item, part_number, description, revision, count and definition, every field quoted; children follow their row) or a .json file. The window lists the same rows, switches between the levels and groupings and shows children under their part, edits a picked row’s part number, description and revision, and exports them. Changing part properties changes no geometry, so it doesn’t evaluate the model or re-seat joints again.