cad-design-tolerances-and-materialslisted

# CAD and 3D Printing: Design for Additive Manufacturing, Tolerances and Fits, and Materials > **Part 3 of 5** of the *CAD and 3D Printing* reference (plugin `cad-3d-printing`), covering §7–§9. Sibling skills: `cad-geometry-kernels-formats-and-code-cad` (§0–§4), `cad-slicing-pipeline-and-processes` (§5–§6), `cad-generative-automation-and-scanning` (§10–§12), `cad-reference` (§13–§18). Section numbers are shared across the set; a reference written as §N → `skill` points into that sibling skill. > > **Currency:** The geometry mathematics and process physics are stable; the code-CAD tooling and slicer landscape moved. See §16 → `cad-reference` for both, dated. > **Scope.** Written for people who write code. **§2–§4 → `cad-geometry-kernels-formats-and-code-cad` are the software engineering > (kernels, scripting, formats); §6–§9 → `cad-slicing-pipeline-and-processes` are the manufacturing physics you need for the > software to produce parts that work.** > > **⚠️ GOTCHA** boxes mark what silently produces a bad model or an unprintable part. > > **The three ideas that organize everything:** > 1. **⚠️ Choose your representation before your tool.** B-rep, mesh, and implicit fields > are not interchangeable — each makes some operations trivial and others impossible, > and **most CAD frustration is a representation mismatch** (§1 → `cad-geometry-kernels-formats-and-code-cad`). > 2. **⚠️ Every export loses something.** STL loses units, topology, colour, and all > parametric in