cdsl-cad/backend/agent/skills/cad-engine/references/part-skills/source/functional/flange-bolt-circle.functional.md

Flange Bolt Circle Functional Skill

When to use

• A flange, circular cover, annular ring, coupling, or flanged sleeve needs fastener holes evenly spaced around a central bore.
• The request mentions bolt circle, pitch circle, PCD, evenly spaced flange holes, or circular pattern of screws.

Do not use when

• Holes are in a rectangular grid, linear row, or mirrored pair on a plate or bracket.
• The part has no central axis or central bore.
• The holes are decorative circular cutouts rather than fastening holes.

Recognition features

• Central bore or hub defines the rotation axis.
• Bolt holes lie on a pitch circle concentric with the bore.
• Angular spacing is equal: 360 / bolt_count.
• Optional counterbores or countersinks remain concentric with each bolt hole.

Core invariants

• Bolt-circle center, central bore, hub, and outer diameter share the same axis.
• Create one correct seed hole with the correct diameter and seat type.
• Circular-pattern the hole feature, not just sketch circles.
• Keep bolt count, pitch-circle diameter, and start angle explicit.
• Add counterbore/countersink to the seed hole before patterning when all holes share the same fastener type.

Parameter roles

• bolt_count controls number of fastener holes.
• bolt_circle_diameter or pitch_circle_diameter controls radial placement.
• bolt_hole_diameter defines clearance or pilot size.
• start_angle controls angular orientation relative to a datum.
• counterbore_diameter, counterbore_depth, and countersink_angle define fastener seating.

Construction sequence

1. Define the central axis from the flange bore or construction geometry.
2. Place one seed hole center at radius bolt_circle_diameter / 2.
3. Create the seed hole as a cut, HoleWzd hole, counterbore, or countersink according to the fastener.
4. Use circular pattern around the central axis for bolt_count instances over 360 degrees.
5. Verify that every patterned hole cuts through the flange and remains inside the outer diameter.
6. Add final chamfers and fillets after the bolt pattern is complete.

Common failures

• Manually placing each hole and producing uneven angular spacing.
• Patterning a sketch without cutting material.
• Using a linear array on a circular flange.
• Choosing pitch circle too close to the bore or outer edge.
• Forgetting counterbore/countersink depth for flush fasteners.

Evidence summary

• Current library evidence: 45 reviewed SCAD58 flange-like models.
• Latest run evidence: accepted atomic and functional insights for circular pattern bolt holes, central bore alignment, and axisymmetric flange bodies.
• Frequent operations in the latest run: CircularPattern, HoleWzd, Cut, Revolution, Chamfer.
• Source: CAD-SkillX offline review of SCAD58 descriptions, STEP summaries, and SolidWorks feature evidence.

Retrieval metadata

Triggers:

• flange bolt circle
• bolt circle
• pitch circle
• PCD
• circular bolt pattern

Secondary triggers:

• flange holes
• evenly spaced holes
• central bore
• counterbored flange holes

Operation triggers:

• circular pattern
• hole wizard
• pattern cut feature
• cut bolt holes

Exclusions:

• linear hole grid
• mounting plate row
• random holes
• side tab holes