Extrude

Theory

Extrude is the most fundamental 3D modeling operation: a closed 2D sketch profile is extended perpendicular to its plane by a specified distance, generating a solid prism. The operation can add material (boss/pad) or remove material (cut/pocket). Some tools support two-direction extrude (symmetric or asymmetric), taper angle (draft), and thin-wall extrude for shelled geometry. In OpenSCAD this is the `linear_extrude()` function.

Application

Every 3D printed part begins with at least one extrude operation. Flat-bottomed parts extrude a profile to full part height. Multi-body designs stack extrusions with boolean joins. For FDM print orientation, extruded directions correspond to high-strength axes (extrusion direction = grain along layer stacking direction). Design profiles in the XY plane, extrude in Z for best layer strength alignment.

Common mistakes

Extruding an open (non-closed) profile generates a surface, not a solid: always confirm sketch closure before extruding. Very thin extrusions (< 0.8mm for FDM) may not form complete walls. Extruding with a taper introduces draft angles: useful for mold design but can cause unexpected wall thickness variation if not intentional.

Related terms: Revolve, Sweep, Loft, Sketch Constraint