I have two different profiles being swept on an inwards spiraling helix. I've gone through every method I can think of but cannot get a smooth transition between the two features. Currently, I am sweeping both profiles for the entire length of the helix, splitting the bodies at the joining point, then using a subtractive combine to get the cut I want in the primary geometry. This still creates a joint that SolidWorks doesn't really like - fillets hit a hard stop at the point, small faces are sometimes created, etc.