How to build a rigid metal frame to resist twist?

[BigBlue1]

Well i can answer the question you posed but it may not be the right question to ask for what you want to do...

If you want a table to resist torsional forces, you need something aptly called a torsion box. The easiest way to visualize this is to think of a frame made of 2x4's, with 2x4 cross pieces on the shorter dimension spaced as appropriate. Then you skin both sides of this box with plywood and glue and screw the snot out of it to the 2x4 frame. This is how you get the stiffest and lightest torsion-resistant "table". The glue is far more important than the screws.

Is that what you need? Dunno, but that is the answer to the direct question you posed.
-Dave

Dave,

The torsion box idea worked well for me. Built it out of 3/4" MDF within the existing perimeter frame under the table top. It is solid enough that the beams don't pull up the legs at all now. Thanks again for enlightening me on this idea. I owe you a cold beverage someday!

Rob

 

[dstig1]

Happy to be able to help! Cold beer? You aren't too far away...I'll be right over!

 

[BigBlue1]

Figured I should follow this up now that the project is completed. Here's the torsion box I built inside the table top frame (minus the final piece of MDF on top to sandwich things). And the finished table. The combination of relief cuts in the maple slabs (about 2.25" deep into the 3" slab, every 3" or so) and the torsion box managed to control the twist in the slabs just fine. No more lift on opposite table legs. Thanks again for the ideas, especially dstig about the torsion box.

Rob

 

[dstig1]

Awesome! Cool table too!