Here I have laid together the two identical/opposite pieces to see how they look. I toyed with the idea of swapping the two sets for more contrast but decided that would be confusing to a viewer.
The next step is to edge sand the exact curves on the edges. You must do this before cutting your shiplap joints. If you cut the joints first and then sand the edges they will not fit properly. Be certain you have the sander base square to the sanding disk or you will have fit problems also. Be sure you use both hands. I had the sander off and the camera in my free hand for the photo, but not a good idea to actually sand it this way!
I did the first part of the sanding as shown above but then followed it up with a sanding disk in my drill press so I was not sanding cross grain.
In the next installment I will describe how to layout and cut the curved edge shiplap joints with only a few handtools and a lot of patience!
-- Kevin, Blue Springs, MO