CAD File Formats — Reading List07.11.26

# 3D / CAD File Formats — Reading List

A short guide to understanding the formats that show up around JewelCAD:
IGES, STEP, STL, SLC, OBJ — what they are, why they lose data, and which
books explain them clearly.

---

## 1. The mental model (read this first)

The confusion comes from mixing three different layers. They are not
interchangeable, and most "conversion problems" are really "wrong layer"
problems.

| Layer | What it stores | Formats |
|---|---|---|
| **Exact geometry** (math surfaces) | NURBS curves and surfaces, trimmed faces, sometimes solids with topology | IGES, STEP, native CAD (`.3dm`, `.sldprt`, `.jcd`) |
| **Mesh** (triangles) | Vertices, triangles, normals — no design intent | STL, OBJ, PLY, 3MF, GLB |
| **Slices / 2.5D** | Closed contours per Z-height | SLC, CLI |
| **View-only** | Frozen snapshot, not editable | JCV, PDF3D, glTF viewers |

### The jewelry-specific trap

JewelCAD is a **surface modeler**: it builds B-spline surfaces, not solids.
Its exports are therefore *open* surfaces. STEP expects closed shells or
solids, so a converter must either sew them (and silently drop whatever
fails) or refuse the file. That is the entire "IGES → STEP drops parts"
story in one sentence.

---

## 2. Glossary

Terms that make the books readable.

| Term | Meaning |
|---|---|
| **NURBS** | Non-Uniform Rational B-Spline — the standard math for free-form curves and surfaces |
| **B-rep** | Boundary representation — a solid described by its faces, edges and vertices plus how they connect |
| **CSG** | Constructive Solid Geometry — a solid described as a tree of boolean operations on primitives |
| **Topology** | How faces/edges/vertices are connected (as opposed to their shape) |
| **Tessellation** | Approximating a surface with triangles (controlled by a tolerance/chord deviation) |
| **Watertight / manifold** | A mesh with no holes and no edge shared by more than two triangles — required for printing |
| **Tolerance / deviation** | How far the approximation may deviate from the true surface; smaller = finer mesh, bigger file |
| **Units** | STL and OBJ carry no units; IGES has a unit flag; STEP carries units explicitly — the source of ×25.4 accidents |
| **Application protocol** | In STEP, the flavour/schema of the file (AP203, AP214, AP242) — decides what data can be stored |

---

## 3. Books — start with these two

### 3.1 *An Introduction to Solid Modeling* — Martti Mäntylä
Computer Science Press, 1988.

The clearest explanation of B-rep vs CSG, why solids need topology, and why
surface models break downstream. Old, but nothing explains these concepts
better.

### 3.2 *Geometric Modeling* — Michael E. Mortenson
3rd edition, Industrial Press, 2006.

Curve and surface mathematics (Bézier, B-spline, NURBS) and how meshes
relate to surfaces. Read the NURBS and surface-representation chapters
only — it is a reference as much as a book.

---

## 4. Books — data exchange and standards

### 4.1 *STEP: The Grand Experience* — ed. Michael J. Kemmerer
NIST Special Publication 939, 1999. **Free PDF from NIST.**

Why IGES exists, why STEP replaced it, what "application protocol" means,
and where translators lose data. The single best text for IGES/STEP
confusion, and it costs nothing.

### 4.2 *Principles of CAD/CAM/CAE Systems* — Kunwoo Lee
Addison-Wesley, 1999 — chapter on data exchange.

Textbook-level comparison of IGES, STEP and DXF, including the honest
limitations of translation.

### 4.3 *CAD/CAM: Computer-Aided Design and Manufacturing* — Mikell P. Groover,
Emory W. Zimmers Jr.
Prentice Hall, 1984.

Dated, but its data-exchange chapter gives the historical context in plain
language.

---

## 5. Books — STL, SLC and 3D printing formats

### 5.1 *Additive Manufacturing Technologies* — Ian Gibson, David Rosen,
Brent Stucker, Mahyar Khorasani
Springer, 3rd edition, 2021 — chapter on data formats.

Explains STL's weaknesses, STL repair, AMF and 3MF (the modern replacement
for STL). Directly relevant to why a JewelCAD STL looks "sliced".

### 5.2 *Rapid Prototyping: Principles and Applications* — Chua Chee Kai,
Leong Kah Fai, Lim Chu Sing
3rd edition, World Scientific, 2010.

Covers STL, SLC, CLI, tessellation and tolerance directly — the vocabulary
of your JewelCAD export dialogs.

---

## 6. Books — NURBS / surface reference

### 6.1 *The NURBS Book* — Les Piegl, Wayne Tiller
2nd edition, Springer, 1997.

The reference. Not a read-through; use it to look things up.

### 6.2 *Curves and Surfaces for CAGD* — Gerald Farin
5th edition, Morgan Kaufmann, 2002.

Friendlier than Piegl/Tiller, same territory.

---

## 7. Free, authoritative, faster than books

- **NIST SP 939** — free PDF; best value per page for IGES/STEP.
- **Library of Congress, "Sustainability of Digital Formats"** — one page per
  format (STL, OBJ, IGES, STEP, 3MF): contents, owner, risks. Good for a quick
  honest comparison.
- **3MF Consortium specification** — free; shows what a modern mesh format
  carries that STL cannot (units, materials, multiple objects).
- **ISO 10303** (STEP) and **ISO/ASTM 52915** (AMF) — the standards
  themselves; for lookup, not for reading.
- **JewelCAD 5.1 specifications page** — read the Import/Export list after the
  books. The phrase "Export (without Boolean Data)" will suddenly make sense.

---

## 8. Suggested reading order

1. Mäntylä — concepts: surfaces vs solids vs topology.
2. NIST SP 939 — data exchange, IGES and STEP.
3. Gibson et al., data-formats chapter — STL, SLC, 3MF.
4. Mortenson or Farin — NURBS depth.

Roughly three weeks of evenings. After that the format names stop being
noise.

---

## 9. The practical takeaway

- **Exact geometry** (IGES, STEP) for editing and design intent.
- **Mesh** (OBJ, STL, 3MF) for printing and machining.
- **Slices** (SLC) when the CAM/printing process wants contours.
- Convert between the two families **at most once**, and do the repair step
  (sew, join, fill holes) on the receiving side, where you can see the result.

Anonymous

CAD File Formats — Reading List07.11.26

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