Virtual-link attachments

Definition#

A Virtual-link attachment is a printable attachment instance hosted by a Virtual link. Use one when a part needs a stable frame-relative position and orientation but does not belong to a real tube, rod, or profile.

Typical examples include feet placed from floor datums, free-standing brackets, instrument mounts, reference-driven fittings, and other local geometry whose parent should be an axis rather than stock material.

Like a Physical-link attachment, it instantiates a reusable type from the frame's Attachments catalogue. The difference is the parent context and the implicit inputs available to that type.

Parent link and anchor node#

Every Virtual-link attachment belongs to one Virtual link and is anchored from a node on that link. Its offset moves the attachment centre along its current direction from that anchor.

The placement relationship is:

``text parent Virtual link + anchor node + direction + offset = attachment placement ``

A dedicated helper link is often the cleanest parent when it encodes real design intent—for example, a short floor-to-corner link that defines both contact direction and attachment orientation.

Direction, rotation, and offset#

The parent Virtual link supplies an initial direction and normal. The attachment then owns its instance orientation:

• Flip direction reverses its axial direction.
• Rotate attachment changes its roll around that direction when its mode permits local edits.
• Offset moves its centre along the direction from the anchor node.

The Flip direction icon is highlighted when the attachment faces opposite its parent link. Its tooltip reports the current direction.

The frame default can orient a newly created attachment toward the nearest terminal or preserve the link's authored direction. New attachments use Independent roll: rotating the guide leaves their absolute normal unchanged. Choose Follow parent to preserve the relative angle while allowing edits, or Locked to parent to preserve it and prevent local edits. Mode changes preserve the current pose.

Offset (°) sets roll about the parent's start-to-end axis, including when the attachment faces the opposite direction. It is separate from the axial Offset (mm) distance. Use the Parent bubble to select the guide. See rotation modes and roll offset for the shared controls.

Dimensions and implicit inputs#

A Virtual-link attachment has Length and Offset expressions. Length can be absolute millimetres or relative to the parent Virtual link's length; offset is always absolute millimetres. Both can reference Frame reactive properties.

Unlike a Physical-link attachment, it has no parent-link radius or wall thickness and no relative-to-radius dimension mode. Its reusable type receives:

• attachment length;
• available Virtual-link distance in each axial direction;
• its own explicit implementation parameters.

Other dimensions—foot radius, bracket width, fastener size, and similar type-specific values—belong to the selected attachment definition's parameters.

Choose a Physical-link attachment instead when geometry must adapt automatically to a real member's section.

End pinning#

Virtual-link attachments use the same Pinned to end position guard as Physical-link attachments.

• With pinning off, offset remains the authored expression.
• With pinning on, the editor derives the offset that keeps the attachment flush with the nearest terminal end.

Creation defaults enable pinning only from a terminal anchor; moving retains the instance's chosen guard. The offset control is disabled while the derived guard owns it, and a length change updates the derived offset.

For a 10 mm-long foot placed on a 20 mm floor-to-centreline guide, terminal pinning derives a 5 mm centre offset. The foot then spans from the floor to 10 mm above it without storing 5 mm as unexplained manual positioning.

Implementation type and parameters#

The Type field chooses a compatible Virtual attachment definition imported into the frame. The definition owns its CSG recipe, parameter schema, body parts, connection ports, and clearances.

The Frame Editor instance stores the selected type and explicit parameter values. It also stores materials and placement. Author or modify the reusable geometry in the Attachment Editor; use the Frame Editor to configure it in the context of a structure.

A Physical-context type cannot be substituted directly because it expects different implicit parent inputs.

Body parts, materials, and connections#

A Virtual-link attachment can resolve to one or several named body parts. Each body part can carry material and manufactured geometry. Separate connection ports identify the selectable regions used by connections and link each region to its owning body part.

Default-based placement uses a body's authored material preference before the Frame fallback. Existing instance assignments do not change when preferences or defaults change. See authored material preferences.

Virtual attachment ports can participate in the same Attachment Connection as Physical attachment ports. This is how a floor foot, for example, can become part of the same printable corner joint as two tube sleeves.

Clearances authored by the Virtual attachment type propagate through its connected printable component just like clearances from a Physical attachment.

Propagation#

A Virtual-link attachment follows:

• movement of its anchor node and parent Virtual link;
• changes to its own length and offset expressions;
• end pinning;
• direction and rotation edits;
• implementation type and parameters;
• body-part materials;
• connected Attachment Connections and shared clearances.

Changing a Physical link's radius or wall thickness does not provide new implicit inputs to a Virtual-link attachment, even when the two happen to occupy nearby space.

Creating and editing Virtual-link attachments#

Import the required Virtual attachment type into the frame's Attachments catalogue. Open + Add, choose the type under Attachments, then select any highlighted compatible node in the 3D view. The editor evaluates every Virtual link in the frame and assigns the attachment to the compatible parent link represented by the chosen node.

The link-local route remains available when the parent matters more than the type: select a Virtual link, choose Add attachment, then select an eligible anchor node on that link. That route uses the frame's default Virtual attachment type.

The main editing actions are:

• rename the attachment;
• move it to another eligible host or anchor node;
• follow its node or parent-link references;
• edit length and offset expressions;
• toggle Pinned to end;
• choose its implementation type and parameters;
• assign whole-attachment or body-part materials;
• flip direction or rotate it;
• start an Attachment Connection from a connection port;
• hide, show, or delete it.

Virtual-attachment defaults seed new instances. They do not modify existing attachments.

Moving an existing attachment#

Select the attachment and choose Move. Green target rings mark eligible nodes on compatible Virtual links. Hover a link near a ring to preview the configured attachment, then click to move it. The move finishes immediately and keeps the attachment selected. Cancel Move or Exit leaves it at its original location.

Moving keeps its definition, parameter expressions, sizing modes, end pinning, materials, visibility, and valid connections and mounted parts. Relative sizes resolve against the destination host; direction and roll transfer with its orientation. A non-circular Physical host keeps its existing roll lock. Destinations that are occupied or would invalidate the configured attachment or its retained relationships are omitted. Physical attachments remain Physical, and Virtual attachments remain Virtual.

Common mistakes#

• Using a Virtual attachment when the part should adapt to tube radius or wall thickness. Use a Physical attachment for member-aware geometry.
• Creating a helper link without design meaning. Its endpoints and orientation should encode the relationship the attachment actually needs.
• Treating offset as relative to link length or radius. Virtual attachment offset is an absolute millimetre expression; relative length uses the parent Virtual link's length.
• Leaving nearest-terminal direction enabled when the authored link direction matters. Choose one direction policy deliberately, then inspect the result.
• Hard-coding a terminal half-length offset. Use Pinned to end when flush placement should survive length changes.
• Assuming Virtual means non-printable. The parent link is non-material; the attachment itself produces printable geometry.

Related learning#

Read the concept series chapter for the illustrated explanation in context.

See Virtual-link attachments in Getting Started for a compact placement example and video before returning here for the complete rules.

Read Virtual links for parent orientation, Physical-link attachments for member-aware geometry, or Attachment Connections for combining connection ports and their owning bodies into printable joints.