How do I make a shelf strong without making it too thick?
I’m in the process of building a big cherry TV cabinet that includes a shelf about 20 in. deep and just over 6 ft. long. I want the long shelf to be strong enough to support books and possibly audio and video equipment. I’d also like to keep the shelf’s height adjustable, which means I can’t attach it to the cabinet back. I’m trying to figure out how to build the shelf so that it still remains in the scale of the entire piece but doesn’t flex or bow. Any suggestions?
Justin Fink, Plainville, CT
Finding maximum stiffness for a shelf is similar to designing any beam: You need to consider its length and load, plus its stiffness and shape. There’s an online calculator for estimating the deflection of a particular shelf at woodbin.com/calcs/sagulator.htm.
According to the calculator, a shelf of 1-1/2-in. solid cherry could support a load of 30 lb. per ft. and only deflect 0.10 in. over the entire length of the shelf. Solid wood is stiffer than plywood, and hard maple is 20% stiffer than cherry, so I would consider using maple for the core and then gluing 1/4-in. or 1/2-in. solid cherry edgeband to each face. A simpler solution would be to face-laminate two pieces of 3/4-in. solid cherry with a 1/4-in.-thick solid-cherry edgeband to match the rest of the cabinet.
One more note: Because the shelf is long and could carry a lot of weight, I would rethink the supports. I’ve had shelves fail when I used small shelf supports under heavy loads. I suggest using either L-style supports or bushings sold for the purpose of strengthening the connection between the cabinet sides and the supports.