Turning operations could do with being enhanced to be able to machine the following model. Ideally, you'd use a grooving tool to make a straight sided groove and then use right and left hand tools to profile the faces that form the sides of the groove. Currently the 'rest machining' options don't allow tools to reach into the groove unless they could have machined the groove themselves in the first place. Here's an isometric view.

and here's what the cross section looks like
