The blueish green lines of the riser is just to give you a visual of what is going on.
The rectangle is a drill jig with drill bushings, drill 4 holes in you riser blocks.
The bottom 2 are sanding pattern, put 1 block on A with dowel pins and the other block on B, mark the the curved lines and cut on the bandsaw and pattern sand each, glue them back together and do it again.
Using 2 different kinds of wood make 2 at a time.
I did NOT use a drill jig for this one.First round
Second round