Assembly Interference Hidden by a Component Pattern
An engineer is assembling a four-bar linkage in Fusion. The base plate is grounded. Two link components are joined with revolute joints, and a coupler is joined to both links. A circular pattern of six bolt components was created inside one link component rather than at the assembly level. During a motion study, the coupler visually passes through the base plate near one extreme of travel. The engineer runs Interference Check on the top-level assembly and gets a clean result. The joints all report as solved, and the timeline shows no errors. The engineer needs to ship a corrected model and a report.
1. Explain why Interference Check returned no collisions even though the coupler visually intersects the base plate, and how the engineer should set up a check that would catch it.
Read the worked answer
Interference Check by default evaluates the components selected at the level where it is run. If the check was run only against a subset, or if the interfering bodies live inside a component whose internal pattern was created at the component level, the check may not have included the relevant body pairs. Visual intersection during a motion study also depends on the position at which the check is run - interference is evaluated at the current joint positions, not across the full range of motion.
Correct setup:
- Select all components in the Interference Check dialog, or explicitly include the base plate and the coupler.
- Enable Include Coincident Faces off/on deliberately and decide whether touching faces count.
- Move the assembly to the extreme of travel where the visual clash occurs, then run the check there.
- Run the check at several positions across the motion range, since a single static check cannot prove clearance through the whole cycle.
- If the pattern is internal to a component, confirm the patterned bodies are included in the selection set.
The judgement: a clean interference result is only meaningful for the selected components at the current pose. It is not a global guarantee.
2. What does creating the bolt pattern inside the link component rather than at the assembly level imply for the engineer's workflow, and what should change?
Read the worked answer
A component-level pattern means the bolts are part of the link component's definition, not independent assembly instances. Consequences:
- The bolts cannot be individually positioned or constrained at the assembly level.
- Interference and BOM behavior treat them as internal features, which can hide them from assembly-level checks and from the parts list.
- Any change to the link component propagates to every instance, which may be desirable for identical links but wrong if the pattern should differ per assembly instance.
Recommended change:
- If the bolts are real purchased parts, insert them as separate components and pattern them at the assembly level so each instance is tracked.
- If they are modeled detail on the link, keep them internal but document that they are not separately checked.
- Re-run interference with the corrected structure.
- Update the BOM so bolt quantities are correct.
The judgement is about modeling intent: pattern location determines whether items are assembly instances or component detail, and that choice drives checking, BOM, and documentation.