CAD Fundamentals

Computer-Aided Design (CAD) is the use of software to create, modify, and analyze digital models of physical objects. In parametric CAD, a model is built as a sequence of features derived from 2D sketches. A sketch is drawn on a plane or planar face and is controlled by geometric constraints (parallel, perpendicular, tangent, coincident, concentric, equal, symmetric) and dimensional constraints (driving dimensions). These constraints capture design intent so that changing a dimension or constraint updates the geometry predictably. A feature is a 3D operation applied to a sketch or existing solid, such as extrude, revolve, sweep, loft, hole, fillet, or chamfer. The model is stored as a feature tree (also called a history tree or model tree), which lists every sketch, feature, and operation in order of creation. This history is parametric: editing an early sketch or dimension propagates changes through later features. Most 3D CAD systems use a right-handed Cartesian coordinate system (X, Y, Z) to locate geometry. Planes (front, top, right, or user-defined) host sketches and define orientation. Reference geometry such as axes, points, and planes supports constraints and feature definitions. Understanding the distinction between sketch entities (2D), constraints (relationships), and features (3D operations) is essential for creating models that are stable, editable, and suitable for downstream applications such as assembly, simulation, and manufacturing.