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Blend Curve

In one sentence: Creates a B-spline that smoothly connects two edge endpoints with a specified geometric continuity (G1, G2, or G3) at each end.

Third-party addon — installation required

The Curves workbench is not included in FreeCAD. Install it via Tools → Addon Manager → search "Curves" → Install and restart FreeCAD.

Overview

Workbench: Curves
Menu: Curves → Blend Curve
Command: ParametricBlendCurve

The blend curve fills the gap between two edges, matching the continuity of each source edge at their shared endpoints.

Continuity options per end

Continuity Condition imposed
G1 Tangent direction matches the source edge
G2 Curvature (magnitude + direction) matches the source edge
G3 Rate of curvature change matches the source edge

The Size parameter controls how strongly the blend curve "pulls" toward each source edge's tangent direction.

Double-click the resulting object to enter freehand mouse-editing mode, where you can drag the size handles interactively.

Common mistakes and pitfalls

Gaps at endpoints

If gaps are visible at the endpoints, the continuity order requested exceeds what the source curve can supply (e.g. requesting G2 from a G1 source). Reduce the continuity order, or ensure the source edges have sufficient continuity at their endpoint.

See also