Physical links

Definition#

A Physical link is a manufactured stock member positioned between two nodes. It represents the real tube, rod, or profile that will be cut and assembled, rather than only the logical relationship between its endpoints.

Physical links own material and section properties, appear in stock-member output, and provide parent geometry to Physical-link attachments. Their placement still belongs to the logical frame: each Physical link is associated with a Virtual-link reference axis.

Logical span and manufactured member#

At first, a Physical link normally follows the same terminal nodes and centre-line span as its Virtual reference. Keeping the logical and physical entities separate allows the editor to express two different truths:

the Virtual link records the intended structural relationship;
the Physical link records the stock material that can actually occupy the assembly.

That distinction becomes visible during reconciliation. Logical links can meet exactly at a zero-thickness node, while real members have a cross-section and may intersect. Reconciliation can move a Physical link's effective endpoints along its reference geometry without moving the logical junction itself.

Section, material, and length#

A Physical link owns a profile, its section dimensions, and a stock material. Dimensions accept literal millimetre values or Frame reactive-property expressions.

Solid Circular: outside radius.
Hollow Circular: outside radius and wall thickness. The wall must be positive and smaller than the radius.
Solid Rectangular: Side A, Side B, and Edge radius. Side A follows the section's local X axis and Side B its local Z axis.
Hollow Rectangular: the same outer dimensions plus wall thickness, which must be positive and smaller than half the smaller side.
L angle: two leg lengths, two leg thicknesses, and their radii.
T tee, I section, and U channel: flange width, overall depth, flange and web thicknesses, and flange-edge and web/root radii. These are solid open sections; hollow construction is unavailable.

Square stock uses the rectangular profile with Side A = Side B. The two fields remain independently editable; bind both to the same property when they should stay equal. Rectangular Edge radius may be zero and cannot exceed half the smaller side. Open-section radii may be zero and must fit the section's thicknesses and edges.

Circular profiles are available without an account. Introducing non-circular members, selecting a non-circular active creation default, or duplicating a document that requires those profiles needs Pro access. Existing non-circular members remain editable without Pro, including dimensions, rotation, and solid/hollow changes where supported. Opening, replaying, importing, archiving, and mesh-exporting supported models remain available on both plans. Current Pro access is checked through the online account response.

Material identifies the stock material. Length is the resolved distance between the current Physical-link endpoints.

Length is derived, not entered directly. It changes when terminal nodes move or reconciliation adjusts the manufactured endpoints.

Terminal nodes and orientation#

A Physical link has an ordered start node and end node. Their positions determine the member's axis, direction, and resolved length; the member also retains its section orientation around that axis.

Changing either terminal is a topology edit. The editor finds or creates a suitable Virtual reference, checks that the member lies on it without overlapping another Physical link on the same span, and updates hosted attachments as part of the same transaction.

Use Rotate link on the Physical link to change its section roll. This affects rectangular and open-section geometry and the clearance needed at junctions; reconciliation preserves your chosen roll. Circular stock looks the same after a roll, but orientation still supplies a local frame for attachments. Circular attachments retain independent authored roll. Attachments on non-circular members lock their roll to the member and follow Rotate link; they cannot be rotated independently. The Virtual reference also has a rotation control: it rotates its radial references and carries the roll into its Physical-link segments, preserving their individual offsets. Rotate the Physical link when only that segment should turn.

Reconciliation participation#

Each Physical-link terminal has a Reconciliation participation control. When enabled, that end is eligible for the reconciliation specification owned by its logical node. When disabled, that member end acts as a constraint rather than an endpoint the reconciliation action may adjust.

Reconciliation is not a generic collision solver and it does not create printable joints. It coordinates real member endpoints around a logical junction. Attachments and Attachment Connections handle the manufactured joint geometry afterward.

Reconciliation is performed only when you explicitly choose Reconcile for one eligible junction or Reconcile all links for the frame. “Automatic” describes how the specification is maintained, not when the action runs. Read the Reconciliation reference for eligibility, constrained members, ordinary endpoint edits, automatic and manual specifications, and the atomic transaction boundary.

Physical-link attachments#

A Physical-link attachment belongs to one Physical link and is anchored from a node on that member's reference span.

The attachment receives resolved parent inputs including:

section dimensions supported by the attachment type, such as circular radius or rectangular sides and edge radius;
wall thickness when the type supports hollow hosts only;
available link length in each direction from the attachment;
the member's local direction and orientation.

Each attachment type declares its supported profiles and constructions. A circular sleeve does not become rectangular merely because its parent changes shape. Within a compatible host contract, changing section dimensions regenerates the attachment automatically. The attachment is a dependent parametric entity, not a detached mesh.

Creating and editing Physical links#

Create a Physical link from the frame-level Add menu or from a selected node, then choose the opposite terminal. New members use the active Physical-link profile and its saved dimension defaults, plus the default material. Each supported profile/construction keeps its own defaults. The frame's reconciliation preference determines whether their terminal participation starts enabled.

The main editing actions are:

rename the member;
change its start or end node;
edit the profile dimension expressions and supported construction;
rotate the section around the member axis;
choose its material;
enable or disable reconciliation at either end;
add a Physical-link attachment;
hide, show, or delete it.

Creation defaults seed new members. Changing a default does not restyle Physical links that already exist.

Properties and relationships#

The main user-facing Physical-link properties are:

Name: its human-readable identity.
Start node and end node: the current manufactured terminals.
Reference Virtual link: the logical axis that contains the member.
Length: the resolved stock-member length.
Profile and construction: circular, rectangular, or an open section; solid or hollow where supported.
Section dimensions: profile-specific expressions and resolved values.
Rotation: the section orientation around the member axis.
Material: the stock material.
Terminal reconciliation flags: whether each end may participate.
Hosted attachments: Physical-link attachments on this member.
Visibility: whether the member is rendered in the scene.

A Physical link cannot use the same node at both ends, extend outside its Virtual reference, or overlap another Physical link along the same reference range.

Manufacturing and export#

STEP export is available to Pro accounts. It preserves Physical links as positioned CAD solids built from their section and resolved length. Joints and purchased parts remain separate faceted components in the assembly. STL/3MF export and stock BOM output remain available without Pro. See Export and build.

Physical links are the source of stock-member information. Before manufacturing, inspect:

resolved length after reconciliation;
section dimensions, rotation, and material;
which attachments occupy or clear each end;
whether cutting, drilling, threading, or bonding assumptions match the chosen attachment system.

Hiding a Physical link affects the scene, not its identity. Delete it only when the member should no longer be part of the frame.

Common mistakes#

Treating the Virtual reference as redundant. It preserves the logical axis and supports other dependencies even when the stock member is visible.
Entering a desired stock length directly. Length follows terminal placement and reconciliation; edit the owning geometry instead.
Using wall thickness greater than or equal to radius. That cannot describe a hollow circular section.
Assuming every attachment fits every profile. Host compatibility is explicit; select or author a type that supports the chosen stock.
Expecting square dimensions to stay equal automatically. Use a shared property expression for both sides.
Changing section properties without inspecting attachments. Link-aware attachments regenerate from the new parent values and may need another visual review.
Disabling reconciliation merely to silence an unexpected result. That changes the member's constraint role; choose it only when the design requires that end to remain fixed.

Watch the Triangle Frame narrated build turn a logical triangle into Aluminium tubes, then compare their manufactured endpoints with the logical junctions after reconciliation.

Read Virtual links for the reference geometry, Reconciliation for explicit endpoint adjustment, Physical-link attachments for member-aware printable parts, or Nodes for terminal placement.