Glossary

Boolean (operation) — combining solids: union (add), difference (subtract), intersection (keep the overlap). OpenSCAD's difference() is how most holes get made.

Bridge — a horizontal span printed between two supports, with nothing underneath. Short bridges (up to ~10–25 mm) print fine; long ones sag.

CAD — Computer-Aided Design: describing shapes with numbers so machines can make them.

Captive nut — a standard nut trapped in a printed hexagonal pocket, giving you real metal threads where you need them.

Chamfer — a flat 45° (usually) cut replacing a sharp edge. Prints cleanly; the FDM-friendly alternative to a fillet.

Clearance fit — a joint with deliberate slack: the hole is bigger than the shaft so parts assemble and move freely.

Constraint — a rule attached to a sketch ("this is 40 mm", "these are parallel"). Constraints are what make a model parametric.

Elephant's foot — the squished-wider first layer of a print. Chamfer bottom edges or compensate in the slicer when it matters.

Extrude — pull a 2D sketch into a 3D solid (FreeCAD calls it Pad). The most-used CAD operation.

FDM — Fused Deposition Modeling: 3D printing by extruding molten plastic layer by layer. The process this guide designs for.

Fillet — a rounded edge. Removes stress risers; one click in parametric tools, awkward in OpenSCAD.

Fully defined — a sketch where constraints nail down every point; nothing can wiggle. The goal before you build on a sketch.

Gusset — a triangular rib reinforcing a corner joint, like the one in the bracket project.

Heat-set insert — a brass threaded insert melted into a printed hole with a soldering iron. The strong way to put real threads in plastic.

hull() — an OpenSCAD function returning the convex hull of its children: shrink-wrap for geometry.

Infill — the internal structure of a print (honeycomb, grid, etc.). Perimeters carry most of the strength; infill mostly keeps the top layers up.

Line width — the width of one extruded plastic strand, usually 0.4–0.45 mm from a 0.4 mm nozzle. Design wall thicknesses as multiples of it.

Manifold / watertight — a mesh with no holes, cracks, or loose edges: a proper solid. Slicers want manifold meshes.

Mesh — a shape described as triangles (STL, 3MF). What the slicer eats; hard to edit.

Module — OpenSCAD's named, reusable feature. A block of geometry with a name and optional parameters.

Origin — the (0, 0, 0) corner of your model's universe. Put it somewhere sensible (a corner or center of the bottom face).

Overhang — geometry sticking out past the layer below. Steeper than 45° from vertical prints without supports; shallower needs them.

Parametric — a model that remembers how it was built, so changing a dimension updates everything downstream. Both sketch-based and code-driven CAD are parametric.

Perimeter — one loop of the outer wall of a print. "3 perimeters" ≈ 1.2 mm wall with a 0.4 mm nozzle.

Press / interference fit — a joint with zero or negative slack: the parts hold by friction.

Revolve — spin a 2D profile around an axis to make a round part (knobs, pulleys, vases).

Shrinkage — plastic contracting as it cools; parts come out slightly smaller than modeled. PLA barely shrinks; ABS/ASA more.

Sketch — a 2D drawing on a plane, the starting point of most parametric features. Rough is fine; constraints make it exact.

STEP — a file format carrying real solid geometry between CAD programs. The polite way to share an editable design.

STL — the standard mesh format for 3D printing: triangles, no units, no metadata. Export it last.

Support — sacrificial printed scaffolding for overhangs. Avoidable with 45° chamfers and smart orientation.

Tolerance — the acceptable error on a dimension, and by extension the deliberate slack you design into mating parts.

$fn — OpenSCAD's "how many segments" control for curves. Higher = rounder = slower.

3MF — a modern mesh format: triangles plus units, colors, and print settings. STL's smarter successor.