Shelf strength - span length. - Woodworking Talk - Woodworkers Forum
 
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post #1 of 5 Old 06-26-2020, 10:48 PM Thread Starter
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Shelf strength - span length.

My son is building a project and is using oak ply for the carcass. It is intended to be a bookcase/shelf as far as I know. He is making it per the wishes of someone and I am a little concerned that the design, while cool looking, may not stand the test of time. The dimensions are approximately: 70" long, 28" high, 14" deep. There is one shelf lengthwise at about the mid point and one vertical piece joined to the underside of the top and the top of the horizontal shelf. There will be a back, so that will add strength.

I am concerned that the shelf, and perhaps even the top, will sag over time. He has proactively mechanically affixed a couple of slim profile metal plates to the bottom of the horizontal shelf to add stiffness/strength.

Are there any guidelines, etc, that can be referenced as to what span would be acceptable prior to sagging, etc? TIA.
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post #2 of 5 Old 06-26-2020, 11:36 PM
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Try this:
https://www.woodbin.com/calcs/sagulator/

Wise men speak because they have something to say; fools because they have to say something -Plato

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post #3 of 5 Old 06-27-2020, 09:44 AM
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How about adding a front, and maybe even a 2nd rear, vertical 1.5" or so lip of hardwood/plywood to reinforce the shelf?

Craftsman 113.29992 Table saw, Craftsman 10" band saw, H. F. 10" drill press, MicroLux 7"x16" lathe, Dewalt 734 planer & Craftsman 6 1/8" jointer
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post #4 of 5 Old 06-27-2020, 12:56 PM
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Quote:
Originally Posted by OldDon View Post
How about adding a front, and maybe even a 2nd rear, vertical 1.5" or so lip of hardwood/plywood to reinforce the shelf?
Maybe like the rear board on this 1970s-style shelf? I made it to match a larger, wider shelf that is actually from the 1970s.
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post #5 of 5 Old 06-29-2020, 10:21 AM Thread Starter
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FYI, he ended up doubling the thickness of the middle, unsupported from below, shelf. So it is not 1-1/2" thick and he added reinforcing steel below, with additional screws on the underside, where they will not be seen. We'll see how it goes.

Thanks for the input, I appreciate it. FWIW, I ran his approach through the "sagulator", with the 1-1/2" thickness, and it judged it as "acceptable" and that was without taking into consideration the additional steel supports underneath and the screws in the field...so I think he should be good.
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