After completion of the torsion box, which weighs nearly 400lb, it was time to build some very sturdy legs.  Here are some of the points that I considered when designing and building it:

• It needs to support the weight of the table (400lb), the weight of the gantry (80lb), a couple sheets of MDF (up to 200lb), etc.  That means that there should be absolutely no joints that only count on mechanical fasteners (screws) in shear.  Pushing down on any point of the leg structure should result in pushing straight through wood, all the way to the floor.
• I own a pallet jack, and wanted to be able to pick up and move around the table with it.  That means that it needed crossbars that were 4" off the ground, that the pallet jack could get under, and lift up.  That also means that pushing up from those crossbars, at any point, must result in pushing only through wood (no screws in shear) all the way to the top.
• I wanted to be able to store extra sheets of wood under the table, inside the wood structure.  Keep in mind that MDF comes in 49" wide sheets, not 48" like plywood.  The gap between the inside of the legs is 52".
• The width of the structure overall is about 59-1/4" (52" + the long side of two 2x4s).  This has the added benefit of being wider than the torsion box, so if you run into it you hit the table first, not the gantry or table.
• I measured the dining room table's height, and it was 30" high.  The torsion box is 5-1/4" tall, which means that the whole table leg structure is 25-3/4" tall.  (That's not how tall the legs are though, since they have a 2x4 on top of them.)
• Each of the legs is an "L" formed by two 2x4s, put together on the long sides.
• Where the lower crossbars contact the legs, add a vertical support below and above to make sure there are no screws in shear.
• Use glue on every joint.  (What a pain.)  This greatly adds to the strength.
• After it's all done, lay some loose 2x4s across the lower cross members to support extra sheet material.  I left them loose in case I ever want to use the space underneath for something else.
• The torsion box is not actually attached to the leg structure.  (But the torsion box + gantry + spoilboard + cutting material weighs about 600-700lb, so it's not going anywhere.)

My construction took four 12' 2x4s, and about 20 regular 8' 2x4s.  It probably cost about $100, and weighs 150+lb.

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