About the Boundary Blend Feature
With the Boundary Blend tool, you can create a boundary blended feature between reference entities that defines the surface in one or two directions. The first and last entities selected in each direction define the surface boundary. Adding more reference entities, such as control points and boundary conditions, allows you to more fully define the surface shape.
The rules for selecting reference entities are as follows:
Curves, part edges, datum points, and ends of curves or edges can be used as reference entities.
In each direction, reference entities must be selected in consecutive order. However, reference entities can be reordered.
For blended surfaces defined in two directions, the outer boundaries must form a closed loop. This means that the outer boundaries must intersect. If the boundaries do not terminate at the intersection points, the system automatically trims them and uses the relevant portion.
Curves selected for blending need not contain the same number of entities.