I recently made a new bookshelf for my room and wanted to share the design.
I came up with the design myself. It is built around a single vertical post (a cedar 4x4, 4 feet long) instead of the more common structure where side walls bear the load. Here is what it looks like:
The shelves are pine 1x8s with holes cut in the middle for the post. They have smaller pieces of pine glued underneath in a T or double-T shape for strength. They are supported by a ledge nailed around the post at the level of each shelf, and by pocket holes drilled into the central post. The following photo shows the underside of a shelf with the structural and connection details:
Because the shelves have no side pieces, bookends are required to keep the books upright. I found a really cool design on Thingiverse that has a figure of a man who appears to be straining to hold up the weight of the books. I printed it on my 3D printer.
This bookend is the largest item I've printed to date. I'm fairly happy with how it turned out (after trimming off some stray filaments). I've yet to trim out the auto-generated scaffolding, and may leave it there to hide a printing artifact (I think the slicing process somehow duplicated the shoulders of the man, but at ground level).