"Murray Peterson" wrote in message
...
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 a 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

For the sheet goods, on average, plywood would be the best, then particle
board, then MDF for initial sag.

I'm a bit unclear on how you're going to build the shelf as a hollow box.
If you're going to go to that much trouble, and then include a steel angle,
I'd suggest just doubling up on the wood for the shelf. Two of the 3/4"
glued-up pine boards would deflect only about 3/32 at the middle under a
distributed 70 pound load (assuming a shelf depth of 12").

You can get an estimate of sag using the Sagulator at
http://www.woodworkersweb.com/sagulator.htm.

todd