[family] drum_tension_lug: drum-shell tension lug

[BenchCAD]

Family

• Family: drum_tension_lug — cat:music-hardware
• Closes [family] drum_tension_lug #10

Reference (issue #10 — SD Sparedrum L20BD)

Datasheet drawing	Part photo

Generated — benchmark views (what the model sees)

Three-view + iso — hard example

Extremes — smallest & largest sampled instances

How it's parameterized

A drum-shell tension lug — a radiused cast body bolted to the shell by two centreline screws, with a rod-thread insert bore at the head end. 8 params, one feature (double_ended = tube lug, rod bore at both ends). Body / hole spacing / bores from the SD Sparedrum L-series; rod threads from Pearl.

Verification (every sampled instance — one non-degenerate solid)

difficulty	body_len	body_h	body_w	hole_spacing	mount_hole_d	rod_bore	solids	valid	bbox (mm)
easy s0	49.55	24.62	22.12	24.1	6.31	5.91	1	yes	22×50×25
medium s0	71.85	23.78	20.37	24.43	7.44	6.33	1	yes	20×72×24
hard s0	109.34	23.94	18.61	24.76	8.25	6.78	1	yes	19×109×24
hard s1	95.32	38.91	20.16	67.64	6.25	5.56	1	yes	20×95×39
hard s2	67.3	24.57	30.21	28.23	7.4	6.32	1	yes	30×67×25

bench2 validate drum_tension_lug --seeds 5 → PASS (8 params complete, difficulties distinct, 15/15 unique shapes).

Checklist

• bench2 validate passes locally (CI re-runs it)
• all three renders committed and match the reference across easy/medium/hard + extremes
• one family, only designs/drum_tension_lug/, body has Closes #10
• DCO-signed; every source/check() cites a real rule or honest proportion — nothing fabricated

Sources used

• SD Sparedrum L-series lug catalogue (body ≈ 42×27×23 mm, hole spacing 25–70 mm, mount Ø6/8, rod [family] round_duct_butterfly_damper: round HVAC balancing damper #12-24).
• Pearl spare-parts catalogue (rod threads [family] round_duct_butterfly_damper: round HVAC balancing damper #12-24 / M5 / M6); width cross-checked vs US8759653B2.
• fillet_r — cast corner radius (proportion). Body modelled as a radiused block; functional features exact.

[github-actions]

bench2 validate

drum_tension_lug

  ✓ family.json: keys + base_plane valid
  ✓ pieces: build(8 params) + PARAM_SPEC + check present
  ✓ PARAM_SPEC: 8 params, all entries complete
  ✓ easy: 4/4 seeds sample+check+build+execute clean
  ✓ medium: 4/4 seeds sample+check+build+execute clean
  ✓ hard: 4/4 seeds sample+check+build+execute clean
  ✓ difficulty separation: difficulties produce distinct programs
  ✓ geometry novelty: 12/12 unique shapes (0% duplicate)
  ✓ solids: every instance non-degenerate, 1 solid(s) each
PASS — designs/drum_tension_lug

Previews: see the previews artifact on this run.

[HaozheZhang6]

Validated in a clone (bench2 validate passes, 15/15 unique) and checked the constraints against the SD Sparedrum L20BD drawing/photo in #10 — the functional dims and the single/double-ended toggle read fine. Two fidelity gaps against the reference, though:

• No rod-thread boss. The real lug threads the rod into a cylindrical boss that stands proud of the head end; here rod_bore is drilled straight into the flat block face, so that protruding feature is gone. It's a discrete geometric feature (not just cast surfacing) and worth adding.
• Domed silhouette dropped. The body notes this, but between the two the part renders as a generic radiused block — nothing in the four views says "drum lug" rather than "small bracket." A modest crown/taper on the top face would recover the read.

The mount-hole and rod-bore logic itself looks right (blind screws up from the shell face, bore on the body axis). Reconsidering the boss is the main ask.

[BenchCAD]

Closing with its issue: #10 is superseded by #78 (stop_bar_tailpiece) per maintainer review — the drum-lug example was too obscure and its reference was arrows-on-a-render rather than a true 2D drawing (standard now codified in #76). The validated implementation here remains referenceable in the branch history if the family ever returns with proper sourcing.