crobar wrote:See attached, the seep results in a shape unsuitable for a stair handrail because of profile rotation
I did and see that it is different because in the attached file there are line segments tangent to the ellipses. Now I see that the desired trajectory is several inclined Arcs of Ellipses separated and connected by tangent line segments.
So... Frenet is used when the Sweep profile is moving along a Path which continuously changes in the X, Y, Z axes (as with an inclined Arc Of Ellipse) but Frenet does nothing when the Sweep is created along a selected Path that only change in two directions. In your example each Sweep along a curved portion should have Frenet ticked (or changed after) to True. Each Sweep should be a separate thing, and the factor that determines where each Sweep thing starts and ends is whether or not it lies on an inclined Arc Of Ellipse or on an inclined line segment. Examine the file posted by @NormandC.
After you create those Sweeps that define the handrail, use Part WB > Boolean Union to create a Fusion of them f you want one continuous handrail.