Maximum shelf length without sagging...


I'm in the process of adding 3/4 inch birch plywood shelves to a pantry. To maximize space, I'd like for the shelves to be 68 inches x 11 inches. Will I need to worry about the shelves sagging if they are supported by cleats along each end and the back? Also, I was planning on gluing and nailing wood edging on the exposed edge of the plywood.
Thanks,
Bob
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Check here: http://www.woodbin.com/calcs/sagulator.htm
And depending on how wide the strip along the front is.
Max
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That wouldn't apply if there's a cleat along the back.
With such a long span, if the load is high, over time the shelf could creep into a "half-bowl" shape that's a bit too low in the middle. I've seen that with a 1/2" shelf that was about 48" span, supported three sides in a kitchen. 3/4" would deflect less, but calculating elastic deflections in a plate supported on three sides is complicated. Creep over time is another problem altogether.
If the strip on the front is deeper than the shelf is thick (i.e 1.5" - 2" instead of 3/4") that would make a big difference. Alternatively, add a centre support. I'd be leery of leaving such a long shelf without additional support.
Mike
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TRY A HOLLOW SHELF APPROACH. Use 3/4" hardwood strips to define a rectangle (or two for a wider shelf) and use "door skin" plywood to "cover" tee top and bottom (glue up). I did one about 32" deep this way - tying the interior frame members with lock dados and employing a couple of cross members. The result was a large, light weight shelf / desktop supported by four brackets across about 80 inches. It holds a TV/VCR and lots of stuff (I made it for a relative - not sure what all he asks it to support.)
wrote:

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I need to worry about the shelves sagging if they are supported by cleats along each end and the back?
Ain't no such thing! Any span will sag under load. You just have to decide how much sag is acceptable. For practical applications, 3/4" book shelves do pretty well with support/separators at 18"+/-. . . or. .. you can build a reinforced beam support for the shelf and get by with less support. It's all in the original design concept. A book on strength of materials will tell you a lot about design. Bugs
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