Arc Skills / Interfaces
Review a mechanical interface specification
Nominal dimensions can look close while their tolerance bands do not overlap. Arc Skills takes both controlled drawings and returns a feature-by-feature fit review with unresolved datum and clearance questions.
Use this skill
Use Arc Skills to review my two mating mechanical Interface definitions.
Inputs:
- Controlled drawings or CAD revisions, units, datums and orientations
- Hole patterns, nominal dimensions, tolerances and fastener clearances
- Loads, thermal conditions, installation sequence and tool access evidence
Return a feature-by-feature table with calculated tolerance ranges, common-frame assumptions, fit findings and owner questions. Do not infer physical interference from nominal dimensions alone.What you provide and what you get
| What you have | How it is used | What you get |
|---|---|---|
| Controlled drawings | Provides nominal geometry and tolerances | Feature comparison by revision |
| Datums and orientation | Makes dimensions refer to the same frame | Comparable ranges or an open transform |
| Fastener and access data | Determines whether pitch mismatch affects assembly | Conditional fit conclusion |
Pitch bands miss by 0.1 mm
Illustrative engineering example.
The fictional plate has two fixed holes at 50.0 ±0.2 mm pitch; the mating bracket specifies 50.4 ±0.1 mm. Both drawings use millimetres, but the example has not yet reconciled drawing datums or hole-to-fastener clearance.
Plate pitch = 50.0 ±0.2 mm → 49.8–50.2 mm
Bracket pitch = 50.4 ±0.1 mm → 50.3–50.5 mm
Minimum pitch-interval separation = 50.3 − 50.2 = 0.1 mm| Feature | Plate drawing | Bracket drawing | Finding |
|---|---|---|---|
| Hole pitch | 49.8–50.2 mm | 50.3–50.5 mm | 0.1 mm minimum gap between specified intervals |
| Datum and orientation | Datum A in source | Datum B in source | Transform/definition unresolved |
| Hole and fastener clearance | Hole diameter TBD | Fastener size TBD | No assembly-fit verdict yet |
| Installation access | Tool approach not supplied | Bracket access not supplied | Assembly sequence open |
The 0.1 mm gap is the minimum separation between the two specified pitch ranges, not a proof that no physical assembly can be made. Clearance holes, slotted features, elastic deformation or different datum definitions might permit mating, but none is documented in the example. A design change should follow a common-frame drawing review and tolerance stack.
Loads and thermal expansion are also absent, so the review cannot close structural or environmental fit. It does, however, isolate the exact geometry question: do the two drawings define the same center-to-center pitch from compatible datums, and what clearance remains at the worst combination?
Compare actual mating features
- Reconcile drawing revisions, units, datums, coordinate frames and mating orientation.
- Calculate each nominal-plus-tolerance interval and the worst relevant combination.
- Check hole/fastener clearance, load path, tool access and assembly sequence.
- State the supported geometry finding separately from the final physical-fit decision.
Questions about this task
Is a nominal 0.4 mm mismatch automatically a failure?
No. Tolerance bands, clearances and datum definitions decide whether the assembled interface can mate.
Can a CAD overlay close the issue?
It can help locate the feature, but controlled dimensions and tolerances are needed for a defensible fit conclusion.
Sources and further reading
- NASA Systems Engineering Handbook: product realization: Interface definition, integration sequence and verification context.
- NASA Systems Engineering Handbook: system design processes: Stakeholder expectations, logical decomposition, functional allocation and design decisions.