When modeling a part in SolidWorks, there are specific situations where a curvature continuous (C2) fillet is desired, but a double hold-line fillet or the “atomic bomb” fillet (split line, delete face, and fill surface) is unable to be created. The delima is how to create these fillets using as few features in the model tree as possible.

Zebra Stripes C1

From the previous posting, we created a model shaped somewhat like an iPhone (see here) and now I have added a protruding feature using the indent technique (see here) which somewhat resembles a nose. After adding the protrusion, a fillet was created at the intersection of the surfaces to remove the sharp edges. Unfortunately, there was no direct way to create a spline section curvature continuous fillet.  The face fillet (w/ double hold line option) was not available as it requires two split lines (one per face).

The best option seemed to create a standard fillet, and then replace the face with a C2 fillet. From the zebra stripes, it is clear there is a tangent transition between the two joining surfaces, and the fillet is composed of two faces. We want to remove these faces using the “delete face” tool, and replace them using the “boundary surface” tool. When using the “boundary surface” tool, use the selection manager (RMB) and choose the loop option when selecting the edges. In this case, the open looped seemed to work better than the closed loop option. These edges will show in the direction 1 curves, and select the curvature to face option.

C2 fillet / Boundary Surface

The next task is to knit the faces together (w/ make solid option), and then view the curvature using zebra stripes. Notice how the transition along the fillet is less sharp indicating C2 curvature, and the fillet is now one face instead of two faces. This only required three extra steps and less features than I have seen using the “atomic bomb” fillet (originally considered massive overkill) which is a technique where you trim or otherwise cut out an area that is causing conventional fillets to fail. After the area has been cut-out, conventional fillets work, and you can fill the cut area with the Fill surface.

Lastly, if you are use to using Pro/Engineer, you have noticed that the Pro-E curvature plots are different from the SolidWorks curvature plots. I have verified this by exporting SolidWorks files as STEP files and importing these files into Pro/Engineer.  Here is an explanation I received from another Pro-E user on this topic:

“Solidworks only does max curvature analysis as far as I know. It doesn’t have Gaussian curvature tool, and that’s why the plots are different.”

Zebra Stripes C2

Gaussian Curvature Plot (Pro-E)