Sweep (Constant Width) creates a surface by projecting a two dimensional curve along a path. The path is not necessarily a straight line. A sweep moves one curve along another and is useful for making many shapes. By creating complex curves for both the axis and the cross-section, complex fillets and blends can be directly achieved in a single surface.
You need to be sure and line up your cross section and your path curve. One way to do this is to create a UCS aligned with the start of the path curve and draw or transform your cross section curve into place.
Swept surfaces are exact.