Fit Spline and Curvature Continuity in SOLIDWORKS

By John Lewis on

Curvature continuity in SOLIDWORKS refers to the smoothness between two adjacent curves or faces at the point where they meet. This blog discusses three types of continuity: C0, C1, and C2. Curvature combs are a good way to visually understand curvature continuity so they are turned on in the following images.

C0 continuity is where two entities touch each other, but that’s all.

curvature in solidworks

C1 continuity is where two entities are tangent. It creates a smooth transition from one entity to another and is sufficient for many applications. However, even though it’s smooth, the radius could be completely different at that point which may affect the esthetics. Esthetics can be important in applications such as automotive parts or consumer products where how it looks and how it feels is critical.

curvature line

C2 continuity is where the curvature is the same where the two entities meet. In applications like the ones mentioned above, this is the desired type of contact.

The fit spline command is an excellent way to generate C2 continuity because it replaces entities that just touch (C0 continuity) or are tangent (C1 continuity) with a single spline which will have continuous curvature (C2 continuity).

smaller line showing curvature

The fit spline command generates a single spline that lays over the top of selected entities. The underlying entities remain and are converted to construction geometry. A tolerance can be assigned which determines how closely the spline adheres to the underlying geometry.

showing curve

Here’s an example of C1 continuity, where the arc is tangent to the two adjacent lines and the resulting revolved feature.

curvature continuity in solidworks

cad drawing

Here’s an example of C2 continuity, where the fit spline command was used to replace the arc and two lines with a single spline and the resulting revolved feature.

curve lines SOLIDWORKS

curvature continuity in solidworks

When esthetics are important and continuous curvature is desired, a fit spline can be an excellent way to accomplish that.

If you enjoyed learning about fit spline and curvature continuity in SOLIDWORKS, be sure to check out TriMech’s Tech Tips for more step-by-step tutorials.