The design for this bookshelf is beautiful, but the execution is not perfect.  The top joint of the semi-circle (where the second horizontal shelf intersects the arc) does not fully close, which leaves a gap between the pieces and means they cannot be screwed closed.  Structurally the bookshelf is still sound, and I think I'll solve the visual issue by wrapping a red cord or ribbon around all of the reachable parts of the semi-circle.  We'll see how it ends up looking, but I'll go ahead and keep the bookshelf.  It's otherwise beautiful and suits my decor well.  Putting it together takes a good amount of time, so set aside plenty to work on it.  Good luck!