Building a large shelf

I'm a total novice when it comes to wood working. I'm looking to build a large shelf inside an 'entertainment center' that was built into my house. The dimensions I'm with here are 60" wide by 28" deep. The front, obviously is open. If I use planks for the top, what I can I do to prevent it from sagging?
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Some ideas (you can combine some of them)
1) Use really thick planks 2) Run a cleat along the back that it can rest on 3) Build a "torsion box" - that is use fairly thin plywood for the top and bottom surfaces and inside use some wood (say 1x2) on edge inside. This gives a very stiff and light shelf. Depth is the key in resisting bending/sagging 4) Put a support in the middle - effectively cutting the span in half. 5) Use very stiff materials - like steel. 6) Fill whatever is resting on the shelf with helium.
-Jack
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    Jack's suggestions are good ones. If you are going to put anything even remotely heavy on the shelf, #3 would be the one to try. If you're going to put something really heavy on the shelf, #3 is still best but use larger lumber inside--or maybe steel.
    Good luck.
            Peter
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On 25 Sep 2003 15:13:10 -0700, snipped-for-privacy@yahoo.com (Dan Wheeler) wrote:

Sixty inches is a large span. A 3" lip on the front and another on the back should provide some stiffness to the large shelf. But in theory, there will be some sag directly related to the load.
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Thanks, guys! I really appreciate the quick responses! I'll give it a try and see what happens!
(Dan Wheeler)

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You need to make the shelf as light as possible but as deep as possible with as stiff a material as possible. Make a fairly thin shelf, say about 1" thick and screw steel strips say 2" x 1/4" onto the front and back edges. Then cover this with wood, possibly the same as the top. The key is in the depth. Without going into detail, double the depth = 8 times the bending strength. Steel is best here as wood can creep over time. You may want to consider a strip of steel in the centre of the shelf as well.
John
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