Wood is not as rigid across the grain as along the grain. Plywood is only about half as rigid as the average hardwood because it’s made of alternating layers of thick veneer. Manufactured wood products are not as strong as solid wood. To find out how much shorter or longer a shelf of another wood should be, multiply the suggested length by the percentages above. Standard shelving dimensions are based on using a wood of average strength, such as walnut. Wood species vary dramatically in rigidity. Thus, the shelf has to be shorter or thicker.įig. Is our cherry encyclopedia shelf average? No, cherry is more than 10 percent weaker than an average wood like walnut or soft maple (Fig. The shelving standards are based on averages. If we cut the butternut shelf in half, it will sag the same amount as the hickory shelf. If we make similar shelves out of hickory and butternut, and apply the same load, the butternut shelf will sag twice as much. In terms of deflection under a load, hickory is about twice as strong as butternut. Some species of wood are much more rigid than others. But this doesn’t tell us the whole story, and that’s why we have to look at one more variable before we can build this shelf with confidence. cherry shelf be to hold up these books? The standards tell us that a wide hardwood shelf that carries a heavy load should be no more than 36-in. The maximum length of a shelf increases when you use thicker stock and stronger material. Here are some guidelines for sizing shelves that are supported at the ends by brackets. With such a substantial increase in rigidity, it’s definitely worth the effort.įig B. If you’re careful, you should be able to get 7/8-in. thick is about 36-percent stronger than a 3/4-in. That’s why wooden joists and steel beams stand on edge. However, add 10 percent to the thickness of a shelf and it’s 21-percent stronger! Strength increases at an exponential rate as you add thickness. The effect of the other two dimensions, width and length, is straightforward add 10 percent to the width of a shelf, and it’s 10-percent more rigid add 10 percent to the length, and it’s 10-percent less rigid. The most important dimensional factor is a shelf’s thickness. This characteristic of wood is called “creep.” Arm yourself for the fight against creep with common sense engineering knowledge about how each dimension of a shelf affects its strength, or rigidity (Fig. The shelf keeps on sagging, a little more each year, because wood slowly but surely changes shape under a load. This sag, or deflection, increases as more stuff is loaded on the shelf over the years. There’s a small sag when you first put weight on the shelf. Even a slight sag sends an unappealing visual message.Ī shelf sags in two stages. A span that holds up weight should look strong and sturdy. So much stuff gets piled on them that they end up sagging like a limp noodle. Have you ever heard a shelf groan? Well, maybe not, but some shelves look like they would if they could.
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