David -

I'm not the machining expert here, but I think Rail Revolve is going to give you the simplest geometry.

1) Draw profile curve. 2) Rail Revolve. 3) Boolean diff with straight line. 4) Fillet to create rounded bottom edges.

The trick to prevent the pinching shown in your example is to insure the end points of the profile curve are tangent. If you want to be sure, Show Points, select a pair of points, and use the Horizontal Alignment tool to line them up as shown in red. File is attached.

Ed Ferguson