At first glance this wide bookcase is pushing, maybe exceeding, the strength limits of most woods, especially pine. However, I assure you that it is not and I thought that I would address the structural choices/solutions that I have employed in this design. I’ll begin at the top and work my way down.
The top shelf is stiffened by an apron running under its rear edge. This apron does double duty as well by adding a small amount of lateral stability to the entire case assembly. To maximize the effect I’ll glue and peg the top shelf to the apron to form a single structural member.
Next down in the assembly is the angled shelf. It’s this shelf that will hold the largest books and therefore carry the most weight. This shelf is made much more rigid by gluing and pegging a wider rear apron board to it. By angling it rearward I moved the center of gravity towards the juncture of the shelf and the rear apron board. This means that the load on the shelf will be more evenly distributed between the two boards. The big bonus is that the angled shelf assembly adds a good bit of lateral rigidity to the entire case.
Below the angled shelf assembly is the drawer bank assembly. At the rear of this section is a housed full-width panel with an apron board above and below. At the front there is an apron board below. The two horizontal boards are connected by dividers. The drawer dividers both stiffen the boards above and blow them as well as transfer the load of the upper shelf of the drawer assembly down to the lower the panel. Which then transfers the weight to the front and rear apron boards and finally into the sides and then to the floor.
Finally, the bottom apron boards, front and rear, are lapped to the sides. While a seemingly simple joint, it creates a very rigid connection that fights to prevent lateral movement. Effectively locking the bottom of bookcase in place. While not strong enough to stop the entire case from racking, when used in combination with all of the above, the joint is one more piece of the puzzle that results in a very strong and stable assembly.
OK, that is probably the most boring post I’ve written to date. But I thought that I should go over the details since the strength of the assembly is dependent on every piece being into place. Like a big game of Jenga, pull out the wrong piece and the whole thing could fall apart.
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Not boring. 🙂 Great illustration and design.
Not boring at all – very interesting. As I was reading it, I was thinking that it blows away all my posts! 😉
Glad you found it interesting. I enjoy your posts very much…so I think you are giving my drivel far too much weight.
Very interesting, especially the explanation about the benefit of the angled shelf.
Thanks Sylvain. You were already onto the importance of the angled shelf. It really is the key to the structural integrity of this design.
Not boring at all. Really enjoyed that breakdown.
Thanks Randall. I’m glad to here you found it interesting.
Looks to me like you’ve got plenty of strength built in. It can be a fine line between getting it right and over-engineering. I think you’ve done a beautiful job here.
Thanks. A full load of books adds a good bit of weight and I wanted to be sure this design would handle that for the long term. Ive seen far too many bookcases with sagging shelves and racked frames. I did not want to add mine to the list. 😉
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