Imported from Sheldon-92/TAD (.agents/skills/hw-enclosure/SKILL.md). Install upstream with npx skills add Sheldon-92/TAD --skill hw-enclosure. Copyright stays with the author.

Hardware Enclosure Design Capability Pack

From PCB dimensions to print-ready enclosure — real tool outputs (STL, PDF, diagrams), not sketches. Scope: IoT / embedded device enclosures. FDM/SLA 3D printing primary, injection molding secondary. Core deliverable: parametric .scad model + STL export + assembly diagrams + dimension drawings. All tolerances, wall thicknesses, and snap-fit parameters derive from manufacturing constraints — never from gut feeling.

Step 0: Pack Prerequisites

• OpenSCAD (parametric CAD + STL export) — macOS: brew install --cask openscad
• D2 (assembly/dimension diagrams), Typst (PDF documentation)
• Optional: ADMesh (STL manifold check), FreeCAD/CadQuery (STEP conversion)

Step 1: Context Detection

Multi-signal: load all matched references. Before declaring ANY deliverable complete, also read its Pass/Fail Criteria section in the matched reference — those are the acceptance rules.

Step 2: Decision Entry Point

Q1 — What stage is the request?

• Full enclosure from scratch → enclosure-design.md first (constraints → type selection → .scad), then pcb-fitting.md
• Existing shell, fit a board into it → pcb-fitting.md
• Deciding what to print it in / production cost → material-selection.md
• How the parts join / open / seal → assembly-design.md
• Handheld or user-facing device shape → ALSO ergonomics.md
• Ready to ship files to printer/fab → manufacturing-export.md then documentation.md

Q2 — Manufacturing method? (drives every tolerance and wall number)

• FDM → tolerance 0.2mm, wall ≥1.5mm (absolute min 0.8mm = 2 perimeters), draft 0°
• SLA → tolerance 0.1mm, wall ≥1.0mm, drain holes ≥2mm in closed cavities
• Injection molding → tolerance 0.05mm, wall ≥1.2mm, draft angle ≥1.5°, uniform wall thickness
• CNC → dogbone relief in inner corners (slot = tool diameter + 0.2mm); export STEP not STL

Q3 — Outdoor / sealed?

• Outdoor → material must survive UV + temperature (NOT PLA >50°C, NOT ABS long-term UV) → material-selection.md
• IP65+ → sealed type: wall ≥2.5mm + O-ring groove → enclosure-design.md + assembly-design.md

Core Judgment Rules (always apply)

1. No invented numbers. Every dimension comes from a datasheet, EDA file, or physical measurement (priority in that order). 编造尺寸/材料参数/人体数据 = FAIL. If the user gives no PCB dimensions, search the board's official drawing.
2. Enclosure type is a reasoned selection, not a default: clamshell (general, serviceable) / slide-in (thin, flat PCB, wall ≥1.2mm) / snap-fit (no-screw consumer look, wall ≥2.0mm, ≥2.5mm at snaps) / sealed (IP65+ outdoor, wall ≥2.5mm + O-ring). State why.
3. Everything parametric. All dimensions as top-of-file variables overridable via openscad -D; bottom shell and lid as separate modules, separately exportable. Magic numbers are forbidden.
4. Mating surfaces get tolerance (lid_inner = shell_outer + 2*tol; FDM 0.2 / SLA 0.1 / molding 0.05mm). Connector cutouts get manufacturing allowance: width +1.0mm FDM / +0.5mm SLA, height +0.8mm. Cutout position error >±0.5mm = connector won't insert.
5. Screw boss OD = screw OD × 2.5; corners get radius ≥2mm (stress concentration); count fastener volume BEFORE finalizing the shell — corner screw clearance is the most common assembly failure.
6. Render-inspect-iterate is mandatory. Never deliver without rendering previews (4 camera angles) and a transparent PCB placeholder block to verify clearances (PCB edges ≥1mm, tallest component to lid ≥1.5mm).
7. Manifold validation is a HARD GATE before STL delivery: openscad --render with zero geometry errors/warnings (plus admesh --check if available). Always export with --render — F5-preview exports can be non-manifold. Failing this gate forbids delivering the STL.
8. FDM printability: overhangs ≤45° or supports; unsupported bridges ≤5mm; horizontal holes as teardrops; first-layer contact ≥20% of footprint.
9. Material-environment compatibility is a required check: PLA not outdoors / not >50°C; ABS not in long-term UV (use ASA); PC when transparency/impact needed; rigid seals don't compress. Recommendations need ≥3 candidates scored in a weighted decision matrix with sourced values ([DATA NEEDED] when missing, [ESTIMATED] for guesses).
10. Antenna clearance: metal enclosures need an antenna window (blocking costs 20dB+); the enclosure is NOT the primary EMI shield — solve EMI at PCB level.
11. Cost honesty: quote mold cost ($2K-15K threshold) whenever recommending injection molding; include post-processing and labor, not just material; if budget can't support molding, say so and state 3D-printing volume limits.
12. Format follows process: STL/3MF for FDM/SLA/SLS, STEP for CNC/molding. OpenSCAD cannot export STEP — convert via FreeCAD or use CadQuery.
13. Docs must match CAD 100%. Every dimension in drawings/assembly guide is cross-checked against .scad parameter values before delivery.
14. Human-domain judgment stays human: appearance style keywords, color scheme, and grip feel are choices to present as options with reasons — engineering numbers (tolerances, wall, clearances) are the agent's to compute.

Quick Rule Index

Enclosure Design (references/enclosure-design.md)

• Constraint gathering checklist (PCB/connectors/battery/environment/method) → §Step 1
• Type selection table + key parameter derivation → §Step 2
• .scad structuring rules (minkowski fillets, boss via difference, $fn discipline) → §Step 3
• 4-angle preview commands, dimension verification, printability optimization (FDM/SLA/CNC) → §Steps 4-6
• Manifold HARD GATE procedure + per-part export commands → §Step 7

PCB Fitting (references/pcb-fitting.md)

• ±0.1mm measurement protocol + connector table format → §Step 1
• Standoff/alignment-pin/edge-slot sizing formulas (M2/M3 numbers) → §Step 2
• Cutout formulas: USB-C 9.5×3.5mm, LED light pipes, button holes, display window steps → §Step 3
• Transparent-placeholder verification checklist + cable routing (bend radius ≥3× diameter) → §Steps 4-5

Material Selection (references/material-selection.md)

• Candidate search queries + supplier list (FDM: Hatchbox/eSUN/Polymaker; fab: JLCPCB/PCBWay) → §Step 1
• Weighted decision matrix template + sourcing rules → §Step 2
• Process match table (FDM/SLA/SLS/molding cost, MOQ, lead time) + stage advice → §Step 3

Assembly Design (references/assembly-design.md)

• Fastening options research (screws+inserts / snap-fit / ultrasonic / adhesive) → §Step 1
• Serviceability tradeoffs (seal vs teardown; consumer ≥20 / industrial ≥100 cycles) → §Step 2
• One-action-per-step sequence rules (pinch force ≤30N, ≤3min hand assembly) → §Step 3
• D2 exploded diagram + fastening detail templates → §Steps 4-5

Ergonomics (references/ergonomics.md)

• ISO 7250 anthropometric anchors (palm width, grip force, thumb reach ≤70mm) → §Step 1
• Form factor rules (edge radius ≥3mm, palm curve R=80-120mm, center of gravity) → §Step 2
• Design language derivation (keywords, colors with rationale, parting line hiding, logo method) → §Step 3

Manufacturing Export (references/manufacturing-export.md)

• Format-by-process table + STEP conversion path → §Step 1
• Per-part export with --render + part-selector .scad pattern → §Step 2
• STL bounding-box verification script (stdlib Python) → §Step 3
• Print profile table (every parameter justified) + release/ package layout → §Steps 4-5

Documentation (references/documentation.md)

• Three-view + cross-section drawing requirements (tolerance and scale callouts) → §Steps 1-2
• Typst assembly guide structure (A4 landscape, BOM, per-step figures) → §Step 3
• Compile + .scad-vs-docs consistency verification loop → §Steps 4-5

Review Checklists (references/review-checklist.md)

• 7 expert personas (mechanical/hardware/materials/production/industrial-design/3D-print/tech-writer), one checklist per capability — run AFTER each capability's deliverable, BEFORE calling it done
• End-to-end acceptance sample (ESP32 + E-ink + 18650 outdoor tracker) for self-testing the whole pipeline

Anti-Patterns

Enclosure Design

• ❌ 硬编码尺寸（magic numbers）→ 必须用变量
• ❌ 忽略公差（配合面无间隙 → 装不进去）
• ❌ 壁厚凭感觉（必须基于制造方式的最小值）
• ❌ 不渲染预览就交付（肉眼检查 = 必须步骤）— 所有成功的 AI-CAD 系统都实现 render-inspect-iterate 循环（来源: MEDA, cad-agent, openscad-agent）
• ❌ 单体建模（底壳+顶盖应该是独立 module，可分别导出 STL）
• ❌ 材料与环境不匹配：PLA 用在室外（UV/热变形）、ABS 长期 UV 暴露（降解）、刚性密封件（压缩不良）— 来源: 多源共识
• ❌ 不计算紧固件占用体积就设计外壳（→ 角落螺丝空间不足是最常见装配失败原因 — 来源: easy-enclosure + NopSCADlib）

PCB Fitting

• ❌ 安装孔位置靠目测（必须用坐标数据）
• ❌ 连接器开口不加公差（插不进去）
• ❌ 忽略 PCB 背面元器件高度（安装柱高度不够 → 短路）
• ❌ 不验证就交付（必须有透明 PCB 占位块渲染）
• ❌ 忘记天线净空（金属外壳挡天线 → 信号衰减 20dB+）
• ❌ 依赖外壳做 EMI 屏蔽而不在 PCB 层面解决（外壳不是 EMI 一线防护 — 来源: Cadence guidelines）

Material Selection

• ❌ 不搜索就推荐 PLA（PLA 不耐温、脆，不是万能材料）
• ❌ 忽略后处理成本（打磨、喷漆、攻丝都是钱）
• ❌ 成本只算材料不算人工和模具分摊
• ❌ 推荐注塑但不说模具成本（$2K-$15K 门槛）
• ❌ 材料参数来源混乱（不同测试标准的数据不能直接比较）
• ❌ 壁厚不均匀（注塑导致缩印/翘曲，FDM 导致强度不一致 — 来源: Cadence anti-patterns）

Assembly Design

• ❌ 只考虑紧固不考虑拆卸（维修时怎么拆？）
• ❌ 卡扣设计没有应力校验（断裂 = 产品报废）
• ❌ 装配顺序不考虑线缆（先盖盖子再接线 = 灾难）
• ❌ 螺丝扭矩不标注（拧过头 = 螺丝柱开裂）
• ❌ 爆炸图没有方向箭头（看图猜装配顺序）

Ergonomics

• ❌ 外形只看内部元器件不考虑握持（方盒子≠好设计）
• ❌ 圆角凭感觉（必须基于使用场景和制造方式）
• ❌ 按钮位置不考虑单手操作（拇指够不到 = 差体验）
• ❌ 颜色选择无理由（'我觉得好看'不是理由）
• ❌ 忽略分型线（在正面留一条丑线 = 廉价感）

Manufacturing Export

• ❌ 导出整体 STL 不分零件（无法分别打印/分色）
• ❌ 不用 --render 导出（F5 预览导出的 STL 可能有错误）
• ❌ $fn 过高导致 STL 巨大（$fn=256 → 文件 50MB+）
• ❌ 打印参数照抄网上不适配当前零件
• ❌ 不验证 STL 尺寸（OpenSCAD 单位是 mm，切片软件可能按 inch 理解）

Documentation

• ❌ 尺寸图不标公差（制造时无法判断精度要求）
• ❌ 装配指南无图（纯文字 = 没人看）
• ❌ 文档尺寸与 .scad 不一致（改了设计忘改文档）
• ❌ BOM 缺少紧固件（螺丝、垫圈、O-ring 容易遗漏）
• ❌ PDF 不含比例尺（无法直接量测）

Anti-Skip Table