Murray Peterson wrote:

"todd" wrote in
:

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.

Are the sagulator numbers good for long-term loading, or just
initial deflection? My experience with purchased bookshelves has
been poor -- shelves that progressively sag more as the years go
by.

BTW, the loading is not distributed -- almost all of the weight is
pretty close to centered.


I'm no engineer... more of a shoot from the hip from experience type.
I think a torsion box with 1/4" glued on ply top and bottom with a
total thickness of 1-3/4" should be strong enough for even the
heaviest stereo equipment.

I think the "sagulator" is just a guide and it has no use in
calculating the strength of engineered assemblies... which is what a
torsion box would be.

Joe Barta