[family] duct_takeoff_starting_collar: round-duct start collar

[BenchCAD]

Family

• Family: duct_takeoff_starting_collar — cat:hvac-ductwork
• Closes [family] duct_takeoff_starting_collar #28

Reference (issue #28 — GreenSeam / ECCO / M&M start collar)

Datasheet drawing	Part photo

Generated — benchmark views (what the model sees)

Extremes — smallest & largest sampled instances

How it's parameterized

A rolled sheet-metal barrel with a stiffening top bead, a ring of trapezoidal base
tabs that bend flat onto the duct, and an optional integral butterfly damper (blade

• diametral shaft). 8 params, one feature (damper). Only diameter varies per
  catalog row; tab count/width are proportion (not dimensioned).

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

difficulty	collar_d	collar_h	wall	bead_proj	tab_h	tab_w	solids	valid	bbox (mm)
easy s0	245.54	90.79	0.51	2.03	26.51	17.48	1	yes	298×298×91
medium s0	291.09	84.28	0.51	2.05	28.83	20.95	1	yes	348×348×84
hard s0	354.78	83.33	0.42	1.57	30.71	24.43	1	yes	414×416×83
hard s1	304.73	154.8	0.47	5.77	19.17	15.62	1	yes	342×337×155
hard s2	204.64	86.34	0.81	1.91	25.8	21.11	1	yes	255×255×86

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

Checklist

• bench2 validate passes locally (CI re-runs it)
• renders committed; matches the GreenSeam start-collar drawing across the 4-20 in ladder + extremes
• one family, only designs/duct_takeoff_starting_collar/ (package files only — refs stay in the issue)
• body has Closes #28; DCO-signed; sources cited, nothing fabricated

Sources used

• GreenSeam tabbed / spin-in start-collar spec sheets (Ø 4-20 in, ~6 in body, 1-5/8 in bead, ~1 in tabs, damper axis 2 in below bead).
• ECCO + M&M submittals (cross-check diameter/height/gauge banding); galvanized steel ASTM A653, 26 ga std / 24 ga option, SMACNA.

Note: ~16 trapezoidal base tabs modelled as a parametric count; the crimp/bead
is a stiffening rib; the damper is the closed butterfly blade + shaft.

[github-actions]

bench2 validate

duct_takeoff_starting_collar

  ✓ 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/duct_takeoff_starting_collar

Previews: the previews artifact on this run.