"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.
--
Murray Peterson