I have in mind to build one or two 13' long shelves for my bedroom wall. It's suppose to hold up textbooks (the heaviest point-source load) and miscellaneous stuff (distributed load).
I thought to try to make a simple shelf out of 3/4" plywood. I never liked the bulky look of support brackets so I went with an L-bracket design, using a plane-ol' miter joint; the shelf is essentially a giant L-shape bracket hung from one of the sides.
My primary concern was the strength of the miter joint and the positioning of shelving bracket (whether to have the joint sit closer to the floor or closer to the ceiling). In the end, I chose a miter joint over a dado or rabbet joint -- for no particular technical reason other than an intuition that it was somehow stronger after spline reinforcement and that it was simple to cut and put together (although glue up was hard).
After glue up and a 4-hour cure time, I tested the joint by mounting it against my shop's plywood wall (16" spacing of screws) and standing on top of it. I'm a small guy, 115 lb, but as a point-source load, I'd be a *seriously* heavy book. The joint deflected 1/4"-3/8" where I stood, as expected, but surprisingly the joint didn't fail -- and this was without the splines! With a combination of some additional techniques:
- Splines along the length of the miter joint
- 2-3 Metal L-brackets, inset on the inner side of the joint (on the shelf surface; I don't completely trust the joint so this is to hedge against catastrophic failure)
- Biscuits for alignment during glue-up (my miter joint wasn't seamless because it was difficult to manage a 8' long shelf. I ended up relying on pin-nails to hold the piece in place while it dried.)
I think this is a viable shelving alternative that's minimalistic and elegant compared to the bulky, expensive, and destructive hollow floating shelves that's the vogue nowadays.
Shelf dimensions:
Leg 1 (Outer length of miter): 5"
Leg 2 (Inner length of miter/effective shelf depth): 9"
Shelf length: 8'
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