Geometry & modeling
Face blend
Definition
A face blend is a CAD transition built between two selected sets of faces rather than from one existing edge. It can bridge connected or disconnected faces and may use rolling-ball or swept-profile construction with explicit continuity, hold-line, trim, and limit controls.
Also known as: face-to-face blend
Updated
How it differs from an edge fillet#
An edge fillet follows an existing edge or chain. A face blend uses two face sets as its primary inputs. That makes it useful when the intended transition belongs between surfaces and the current edge is fragmented, unstable, or does not exist.
Onshape's Face Blend documentation allows the selected faces to be connected or disconnected. The blend can remain attached to the part or be created as detached surface geometry, which then needs its own trimming and joining workflow.
Cross-section and boundary control#
Onshape documents two broad cross-section methods. Rolling Ball creates a curved blend between the face sets. Swept Profile carries the blend cross section orthogonally along a selected spine. The tool also offers circular, conic, chamfer, and curvature controls plus asymmetric sizing.
Hold lines can constrain where the transition runs. Cliff edges, caps, and plane or face limits control how the blend terminates when its natural extent crosses surrounding boundaries. These controls make a face blend more deliberate than asking an edge fillet to infer every boundary from one edge chain.
Continuity and limits#
Side continuity defines how the blend meets its source faces. Tangent or curvature-continuous joins can improve reflection flow, but the result still needs surface-continuity inspection. A smooth stripe pattern at the join does not prove suitable wall thickness, draft, stress behaviour, or manufacturing access.
A face blend can also change topology and downstream references. Validate the joined solid, critical dimensions, drawings, and exported body after the blend is added or revised.
Sources
Related terms
Fillet
In CAD, a fillet is a transition surface that replaces a sharp edge between adjacent faces. It is commonly controlled by a radius or width and may use constant, variable, asymmetric, conic, or curvature-continuous geometry depending on the CAD system and design requirement.
Surface modeling
Surface modeling creates and edits zero-thickness faces that define the outer boundary of a shape without enclosing material or volume. It is used for complex curvature, product styling, face repair, and hybrid workflows where surfaces are later stitched, knit, or thickened into a solid.
Surface continuity
Surface continuity describes how smoothly adjacent curves or surface patches meet. G0 continuity joins them at the same position, G1 also aligns their tangent direction, and G2 additionally matches curvature so the rate of bending flows across the boundary.
NURBS
NURBS are mathematical curves and surfaces that can represent both simple shapes, such as lines, arcs, and circles, and complex freeform surfaces exactly. CAD kernels use them for the faces and edges of B-Rep solids that are not simple planes or cylinders.