Parametric Design

Parametric design is a CAD methodology where geometry is driven by parameters—dimensions, constraints, equations, and relationships—that define and control the model. When parameter values change, the model automatically regenerates to reflect the new values while maintaining design intent. This enables rapid design iterations, design tables for multiple configurations, and easy adaptation to new requirements. Parameters fall into several categories: (1) Dimensional parameters control sizes (lengths, angles, radii). (2) Geometric constraints control relationships (parallel, perpendicular, tangent, concentric, equal, symmetric). (3) User parameters are custom variables (material properties, design factors, counts) that can be used in equations. (4) Reference or driven dimensions display calculated values but cannot be directly modified. A parametric model is built on a feature tree or dependency graph. Each feature references previous features, creating parent-child relationships: the parent is created first, and the child depends on it. Modifying a parent feature automatically updates all dependent children during regeneration. Understanding this dependency structure is essential for robust modeling. Design intent is captured through careful use of constraints and equations. For example, instead of dimensioning each hole individually, you might dimension one hole and use an equal constraint for the others, or use a pattern with a count parameter. Equations allow relationships like: width = 2 × height, or hole_spacing = length / (count − 1). When the length changes, the spacing updates automatically. Parametric models can fail if constraints are overdefined (conflicting constraints) or underdefined (insufficient constraints). A well-constrained sketch is fully defined with no degrees of freedom remaining. Adaptive modeling allows underconstrained components in assemblies to automatically adjust size or position to satisfy assembly constraints when other components change.