If you go to 1 thick material instead of 34, that gets you another 10 or so of width.How do we make sure those shelves dont sag, or the floating countertop is solid In this first post Ill share pointers to several useful calculators, and touch on good guidelines and a few techniques to avoid finding yourself with a beautifully crafted piece of furniture that, under duress, starts looking like this.And over many years, the sag of a shelf tends to increase by as much as 50 as it is stressed repeatedly in the same direction.
So a good target for initial allowable sag is 0.02 per foot or less. Dont Worry About Small Shelves Many cabinet designs call for the flexibility of adjustable shelves. Unfortunately, however, adjustable shelves are more prone to sagging than fixed shelves, as anyone who has loaded a cheap Ikea bookshelf with all of their college textbooks can attest. This is a consequence of many factors in that 50 hand-me-down bookcase. But with a bit more planning and design consideration (and better materials), sagging can be wholly avoided. However, for small shelves, sag is not really a problem and one can just ignore considerations of sag for typical loads. Whats small The most frequently used quality materials for custom-built wood shelves are 34 thick plywood, poplar, or pine; definitely avoid the melamine-laminated composite shelving and MDF. And a typical shelf load to plan for is 20-40 per foot - libraries often plan for 35. A 30 wide adjustable shelf that is 10 deep, made of any of these three (plywood, poplar, pine) materials, will have an acceptable sag for a load of up to 35 per foot, or about 90 for the entire shelf. Deeper or shorter shelves Or anticipating less weight Sag definitely wont be a problem for those small adjustable shelves. But fortunately, as you get narrower, its less likely that youll get to 35 per foot. A 6 deep adjustable shelf will probably not get loaded more than about 20 per foot - made of any of those materials, a 30 span would still be fine. Of course, if youre loading your shelves like that coffee table above, all bets are off The Sagulator. But dont worry - these are online calculations that hide the messy math, at least to start out with Ive come across a few calculators online, but the Sagulator seems to be the best one so far for ease of use, flexibility, and options that allow for common solutions that woodworkers use to counteract sagging shelves. Select the material, enter a few numbers, and voila, it estimates the total and per foot sag, and even makes a judgement call, summarizing the results as one of Excessive, Borderline, or Acceptable. Counteracting Sag If your design sags too much, there are a few simple solutions, and a few more involved design changes. Lets assume, however, that changing the size of the shelf, and how much load or weight you need it to support, is not an option. For the examples below to give a sense of how much each design change can help, lets focus on a 10 deep shelf, made of 34 thick plywood shelf. Then we can find the maximum width shelf that will give an initial sag of 0.02 per foot. Of the three most common for basic shelving - poplar is the stiffest, with pine and plywood just slightly less stiff (or, in engineering-speak, having a lower modulus of elasticity). However, switching to even less elastic (and more expensive) oak could push your design into safe territory; if the shelves will be painted, the material choice is almost irrelevant except for cost (and availability). Pine (spruce): 28 Plywood (fir): 28 Poplar: 28 Oak: 32 If budget is no barrier, a beautiful hardwood like purpleheart is even stiffer, and could get you a 35 wide shelf, but that would be a very unconventional (and wasteful) use of that expensive wood Thicker Materials Though Lowes or Home Depot only carries boards in 34 thickness, and plywood thicker than 34 is not very common, you can usually find thicker materials at a specialty lumber store.
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