If you want a bow with a round cross section, you have to start out with a very small-diameter stave,(like an inch or so, maybe less) so the back will have a high crown (naturally rounded) and work the belly into a round cross- section from there. Robin Hood's bow, as well as any other English bow, was an English Longbow design, did not have a round cross section, but a D cross section, with the flat of the D being the back and the rounded side being the belly. It might seem from the movies that these bows had a completely round cross-section, but they did not.