Originally Posted by High Seas  Just another thought on comparing MDF and plywood (Baltic Birch -- very nice, but any marine ply would suffice -- no voids, good glues) for the torsion box:
Sheer failure in the webs.
MDF will sheer when loaded due to its lack of "grain" |
If your talking about the edge of the MDF, I'll disagree. Bond the skins with epoxy, which will soak deep into the edge of the grain, and it'll be very difficult for the edges to shear off. If you're talking about the skins, then I'll agree a little. But the quantity of interior members greatly affects the load required for this shear to occur. If you want a stronger box, increase the density of the core.
Also, at what force do you think this shear will occur? A cheap hollow core door, with 1/8" masonite skins and a
CARDBOARD core, will support a few hundred pounds pretty easily.