I did this piece to show how the different router bit profiles affect the shapes of the added contrasting wood once you start turning into that shape. If you take the rectangular piece as 12 oclock, it was done with a straight router bit. A flat piece of wood was glued into this groove. 1 and 2 oclock were done with a 90 degree V bit or in this case a straight cutter mounted at 45 degrees so the 90 degree corner did the cutting. A Square "dowel" was glued in this groove. The 3 oclock position was a ball end cutter with a dowel glued in the curve. You can see how the shapes of the router bit affects the design of the contrasting piece as you cut through it or as viewed from the end. This also shows some of the problems and design opportunities. If you look closely at the 12 oclock piece you will see that there is a slightly larger glue line on one side. It's very difficult to get a router bit to track perfectly straight when presented to the wood in a groove cutting orientation. Normally on flat work I will make 2 cuts so the cutter is cutting in a clockwise direction and gives a straight line. In this case it was one cut and the cutter wants to follow the grain if it can. The other thing to notice is they appear to be stacked on top of one another. You can eliminate this to some degree by cutting 90 degree mitered points on the ends so they run together. That is quite challenging to do especially with the round dowel. It also leaves a gap in the dead center that must be addressed or covered up. Just something to think about when you do these things.