Best material for long shelves

I am building a 6 foot long shelf that is going to be supported at the ends (no option of support in the middle). The shelf needs to support about 50- 70 pounds of weight (stereo equipment), so the "sag" (or deflection) in the center is going to be a problem. I plan on building the shelf as a hollow box, and using steel angle iron on the inside as a stiffener.
Just out of curiosity -- what commonly available wood product is best for resisting deflection under a continuous load (i.e. shelving)? The easily available ones at my local lumber store are: laminated pine, mdf, playwood and particle board, I am assuming that the laminated pine would be best, since all the grain is running longitudinally. Is my assumption correct?
--
Murray Peterson


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Murray Peterson wrote:

Google torsion box shelving. You might be approaching this the wrong way.
R
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Thanks -- tosion boxes look like the right way to go.
--
Murray Peterson


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Take a look at the aluminum pieces used to hold drop ceilings. On edge they seem very strong. They are a T so you have some options on how to mount them to the shelf. ...thehick
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ends
50-
the
IMHO, you need to revisit your design- there is always a way to add support in the middle, even if it is only matte-black metal rods seated in shallow holes so they don't float around. If the planned load for the shelf needs to be centered, use 2 vertical rows of rods at the 1/3 and 2/3 points. Sounds like you are basically building a bookcase. Can you put a back panel on it? That will stiffen it up considerably. I'd use 3/4 pine plywood, or even 2x lumber, for that long a span. A glued and nailed hardwood front strip stiffens plywood, and dresses it up a bunch.
We could make a lot better suggestions if you could describe the proposed shelf better, or even post a diagram of the design, or a picture of the hole where it will go, somewhere.
aem sends...
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The shelf runs diagonally across a corner of a room, attached at the ends to each side wall. Under the shelf is a 52 inch projection television, which is sitting in that corner of the room.
--
Murray Peterson


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Murray Peterson wrote:

If you like a heavier look, you could use 3/4" material (plywood or solid wood) and simply put a 3-1/2 piece on the front and rear edges (and upside down U and know you don't need to make a complete box). That would hold a huge weight.
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On Mon, 09 Jan 2006 02:37:20 GMT, Murray Peterson

A 6' diagonal? That seems excessive, but if that's what you want..
Look at www.goedjn.com/sketch/shelf.gif
The top image is a top view of the layout of your supports. You could get away with using 1x6s for these, but if you use 2x4s, then you'll be able to sleep on the thing. The ones that run along the walls should be fastened at each stud with two 2.5" deck screws.
The two lower diagrams are details of the joint where the outer crosspiece meets the the side-rails. If the thing is going to fail, that's where it will do it, so use tennons, a glue-block, and more deck-screws.
The inner diagonal is just a stiffener, so you can skip the tennons, as long as you screw the plywood upper deck to both the rails and the diagonals.
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It actually is a bit short of enough -- the front edge of the shelf ends up about 6 inches behind the front of the TV. That's what I get for having a TV that size :-)

Thanks for the effort. I don't have a problem with the supports, since I have a stud on each wall at the right point. I was worried about sagging, but I'll be trying out the torsion box suggestion. Sounds like a good one.
I'll try to remember to post a link to some pictures of the completed job.
--
Murray Peterson

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50-70 lb 6 ft no deflection, a 4x12. stone fireplace lintel, maybe 4x12 isnt enough, have fun. Or put in supports.
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Murray Peterson wrote:

First, 50-70 pounds for a shelf is nothing, but it the length is a problem. It is only a problem if you are thinking about 3/4" material. So, use 2" material, e.g., 2x8, 2x10, 2x12 solid wood (should be available at any lumber store). Any kind of plywood would be ok, but it needs to be at least 1-1/4" thick. Forget mdf and particleboard for what you are talking about. Don't know anything about laminated pine, never seen the product.
A hollow box is ok, but much more work than just using 2" material. If you insist on a box, you certainly don't need any metal stiffener.
BTW, you ought to visit a store, lay a 2x 8 down on the floor supported by a couple of of 2 x4's spaced 6 feet apart and then stand in the middle of the 6 foot space. You will see how much the 2x8 deflects. Caution: don't do this if you weigh more than 400 pounds.
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ends
50-
the
hollow
for
easily
playwood
best,
correct?
He could probably get away with a 3/4" board if he also used a 2x4 as a stiffener throughout the length of the board.
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Murray Peterson wrote:

How much is too much? If I = bd^3/12 = 7.25x1.5^3/12 = 2.04 in^4 for a 2x8 and the load W = 70 lb and Hem-Fir has a modulus E =1.4E6, the deflection d = 5WL^3/(384EI) = 5x70(6x12)^3/(384x1.4E6x2.04) = 0.12 inches.
More porcupines :-)
Nick
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Murray Peterson wrote:

Put a 6 foot 2x8 on the bottom in the middle of the shelf.
--
Joseph Meehan

Dia duit
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Take a look at the wire shelving at LOWES or HD. They're very sturdy, cost a helluva lot less than comparable size wood, need no finishing, can be cut to size, etc, etc,
<rj>
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Build the shelf like a floor structure, using 2x4 "joists" at 16" OC (on edge, NOT flat). Assuming the shelf is less than 16" deep, you should only need a 2x4 along the front and another along the back (I'd add cross blocking every 2' or so to help stiffen things up). As long as you anchor the ends well, this should hold plenty of weight. You could even stand on it if you wish. Then cover this with the decorative covering of your choice (plywood, paneling, sheetrock, or whatever).
If weight is an issue, you could probably build a torsion box out of 3/4 inch plywood. I'd make it 3-4 inches thick if I were doing it.
Good luck!
Anthony
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HerHusband wrote:

Why such heavy skins? Unnecessary weight and expense.
R
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Oops... Typo... :) I meant 1/4 inch plywood for the skins of the torsion box, but I'd probably use 1x material or 3/4" plywood for the internal structures.
Anthony
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