OpenSCAD Organic — Figurines and Miniatures

Builds on openscad-cad (§2 render/export commands still apply) and follows scad-modeler discipline (§0 project facts, calculations before geometry, validation). This skill adds what neither covers: smooth organic surfaces and print-safe fine details in a CSG modeler.

Not sure which skill to load, or where a fact lives? See ../references/retrieval.md — the routing table (skill choice, passport format, abstention).

0. Before anything else

1. Load openscad-cad (render/export) and, for 2+ interacting parts (articulated limbs, head+body+base), scad-modeler (planning, tolerances).
2. Read ../INCIDENTS.md — a logged organic bug never re-read will recur.
3. Require BOSL2 (use <BOSL2/std.scad>): skin(), path_sweep(), bezier() live there. No BOSL2 — single-hull blobs only, say so honestly.
4. RESEARCH-FIRST for replicas (INCIDENTS 2026-09-09): before modeling a real-world object, use agent-reach (Exa/GitHub/web) to fetch REAL dimensions + print practice. Never model from one artwork photo alone. v1 without research = blockout, not a model.

1. Core techniques (use in this order)

1.1 Piecewise hull, never single hull (jack rule)

One hull() over all spheres = plastic-wrap box, not organic shape. Connect CENTER sphere to EACH satellite separately (makerblock jack trick):

for (i = [0 : len(pts)-1])
  hull() { sphere_at(center); sphere_at(pts[i]); }

Each satellite = one limb joint, muscle bulge, cheek. Concavity survives because hulls never span the gaps between satellites.

1.2 skin() for bodies (profiles, not primitives)

Body = list of 2D cross-sections at heights, connected by BOSL2 skin():

use <BOSL2/std.scad>
profiles = [circle profile at z=0, ellipse at z=10, smaller at z=20];
skin(profiles, slices=8, refine=12, method="distance", caps=true);

Rules: same winding direction every profile; method="distance" when point counts differ; slices for smoothness; NEVER self-intersecting (cryptic CGAL). Head/hands = high-res profiles; torso = fewer.

1.3 path_sweep() for limbs, tails, horns

Fixed 2D profile (circle/oval) along a 3D path, ideally a bezier():

path = bezier([p0, p1, p2, p3], N=32);
path_sweep(circle(d=4), path);

Twist/scale along path for claws, ears, decorative ridges. Limbs print best along their own axis — orient the sweep, not the slicer.

1.4 Details ON the surface, never separate bodies

Eyes, wrinkles, scales, rivets: small hull()/sphere() blobs unioned onto the skinned surface (adeptus-dad ork-plating pattern: VNF surface → offset outward → union). Separate floating bodies = slicer artifacts. Detail minimums (0.4 nozzle): wall >= 0.6, feature >= 0.5, gap >= 0.3. Below that: 0.2 nozzle or resin — say so, do not fake it.

2. Print discipline (FDM)

• Supportless first: angles <= 45 deg from vertical; add Cura/Orca "Make Overhangs Printable" only as fallback (visible ramps).
• $fa/$fs globally, never $fn (Wikibooks rendering guide); $preview low, full render high: FN = $preview ? 12 : 72;
• Details in XY plane (resolution lives there); layer 0.1-0.12 for faces.
• minkowski() for fillets LOCKS final size with resize() (infinityplays constrain pattern) — minkowski grows objects, compensate or oversize.
• convexity >= 2 for folded/holed shapes (preview correctness).

3. Validation (before STL)

1. Render + LOOK (openscad-cad §2): front, top, iso — gross errors.
2. Manifold NoError + watertight (scad-modeler scripts where present).
3. Dimension check: bounding box vs brief; detail calipers (>= 0.5).
4. Self-intersection hunt: any skin()/sweep added since last render gets a solo render first — CGAL errors come from the NEW profile, not old code.
5. Proportions as numbers (P6): write the ratios you researched in step 0.4 into the .scad BEFORE modelling, one per line — // PROPORTION: z/x = 2.6 +- 0.05 (bbox) or // PROPORTION: w_x@0.9 / x = 0.55 +- 0.1 (slice width at 90 % height). validate_scad.sh checks them (CHECK_RESULT proportions).
6. Shape vs reference (P6): cut the reference photo out to a silhouette (dark shape on white, or transparent background), save it next to the .scad, and declare // SILHOUETTE: front ref_front.png >= 0.85 (front|side|top). Needs Pillow (bash scripts/setup_env.sh). A raw photo with clutter measures the clutter.

4. Output conventions

• One project folder per figure; .scad source is the deliverable.
• PNG renders (--render, not preview) in the final response.
• README: render/export commands, confirmed vs estimated dims.
• Real bug this session -> ../INCIDENTS.md entry before finishing.

Reference files

• ../references/retrieval.md — routing table: which skill to load, passport format, abstention rule.
• references/organic-patterns.scad — copy-paste: piecewise hull chain, skin() body template, sweep limb, detail-on-surface, snap-fit base.
• references/miniature-tolerances.md — FDM detail minimums per nozzle, supportless angles, VNF/skin pitfalls (self-intersection, winding).
• ../INCIDENTS.md — shared log with scad-modeler. Read before, append after.