Bookshelf question

In your experience, what material is better resistant to sagging from the weight of heavy books, 3/4" plywood or 3/4" solid lumber? In the case of solid lumber I suppose it could depend on a number of factors, not the least of which is the species of wood, but let's just assume a variety of the most popular species (oak, walnut, mahogany, maple, cherry, etc.) and good straight kiln-dried lumber that is showing no outward signs of stress or a tendency to warp. Would that resist sagging better than a good quality plywood faced with the same species of wood?
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anything will sag over time. When I build bookcases, I always put in dividers. This not only allows you to catagorize and separate books, but it makes the unit much stonger. No sag.
If you are making movable bookshelves, you may need to reinforce the board to eliminate sag. A simple 1 X 2 fastened to one or more edges will usually do the trick.
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I can't belive no one answered this yet... use the sagulator http://www.woodbin.com/calcs/sagulator.htm
Look at the end of the list of materials to find plywood.
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SonomaProducts.com wrote:

Heh, the "sagulator". That's quite the spiffy little resource; thanks. :-)
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Steve Turner wrote:

http://www.woodbin.com/calcs/sagulator.htm
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Steve Turner wrote:

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Steve Turner wrote:

Oak. Last set I did...
http://www.mikedrums.com/bookcases.jpg
...with four foot shelves, I had to put two: front and back.
While I was building them, I did different weight tests on different configurations (loaded with books and left for a few days) and that was the only one that resulted in no (negligible) sag.
I've been back, a couple years later, and still no sag under load.
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-MIKE- wrote:

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On Sun, 27 Sep 2009 17:41:43 -0500, Steve Turner

Ply or solid wood is about equally sag resistant. The book shelves I built have a 1.5" wide pine lip on the front and the back of the 3/4" ply shelf. The lip hides the plies and adds a lot of strength. Even with that, try to avoid a span of more then 30". Books are heavy.
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wrote:

Ignore 'sagulator'; it omits age and moisture, both of which can dominate the bookshelf situation. Flakeboard, plywood, and oak are the worst. That's because the glue (or in the case of oak, the sap) is important in these materials, and it will absorb moisture and stretch, or expel moisture and shrink, in ways that strength-of-materials calculators ignore (because the load tests are too quick to see the effect).
Pine, with paint, is a very good shelf material: lightweight, stiff, cheap. If you want a fast-drying finish, some woods without lots of sappy knots will only need a wipe-on shellac. My last project used knotty pine, and came out well, BUT the plan was dark-stain and polyurethane varnish: the finishing steps took a week (sand, wood-conditioner, dry time, stain, dry time, touchup stain irregularities, dry time, shellac, clear polyurethane, dry time). Next time, a different plan.
Most of the shelf surface is invisible in use: a decorative strip on front, or (better for stiffness) a front skirt board that adds some depth, is an appealing design choice.
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I used red oak, with a 1"x2" front lip at 90 degrees (like angle iron) and after 11 years of holding hundreds of computer books, there ~might~ be a 1/16th inch of sag in the middle. Lip was attached using biscuits and glue, shelf was attached into dado on upright with glue and screw, and some plugs to hide the screw heads along the side. I made 2 cases, 36" wide 8" deep, 8ft tall. ymmv. Royce
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Just to amplify on this, that front lip 2x1 inch on a 1x7 inch flat shelf is about half the stiffness of the whole assembly.
If pine is half the cost and half the stiffness of oak, we can calculate the cost and stiffness of a shelf design.
Oak 2" lip / oak 7" shelf: cost 9, stiffness 15 Oak 2" lip / pine7" shelf: cost 5.5, stiffness 11.5 Oak 2.25" lip/pine 7" shelf: cost 5.75, stiffness 15
Oak makes a pretty face, pine holds its share of the load; I'll take that third design and call it good.
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Plywood shelves sag more than solid hardwood of the same dimensions. Even without a preciase numerical answer, a few moments of reflection will make it clear that this is inevitable, given the softwood cores and internal voids and patches of typical plywood. With that said, I'm reasonably satisfied with 3/4" plywood shelves for spans shorter than 30", given normal sized books packed end to end on the shelf. Substantially heavier loads, such as a set of encyclopedias, beg for a different solution.
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Steve Turner wrote:

The primary issue is what are you trying to do? Looks, ease of build, cost of materials, and so on are the key factors. Oak is certainly stronger than plywood, and looks a lot better. Look for quarter sawn more than flat sawn lumber. Also, when you buy 3/4" Hardwood at a mill or lumber yard, you generally get more than 3/4, often 7/8". Fixed shelves are stronger than floating, Face frames are really strong if shelves are attached on all four sides and sag is then almost a non-issue.
Right now I'm looking at some cheap ass book shelves my wife bought about 15 years ago. They are cheap veneered particle board. The shelves are floating 3' long that I attached to the back, no face frame and loaded with computer books. The sag is about 1/16". If they had a facing, they wouldn't have sagged at all. If they were oak, I don't think they would have sagged either. Personally, I like bookshelves with attached sides and a face frame. Floating shelves are about never adjusted. Once you decide where to place the shelves, they pretty much never move again, so might as well make them permanent and design something strong and nice looking.
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wrote:
Fix your clock dweeb.
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snipped-for-privacy@no.com wrote:

My clock doesn't need fixed, twit!
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But your syntax do.
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