I’ve nearly completed my torsion box for my super-duper flat and stable table.
It’s made of 1/2" MDF with 2" tall core supports, spaced at about 2" apart. I have the top and bottom glued and Brad nailed, I’m going to caulk it with acrylic caulk tonight and then give it a few coats of heavy duty polyurethane to make it waterproof and scratch resistant.
My question is: where do I go from here? I need to make a table (carcase) to go under the box to hold it up and make room for the shop vac. I could nail or glue it to a base table, but I don’t want the inevitable bending that take will experience to exert torsional forces on my box. I could set it on or strap it to the top of a table base, but I’m concerned about vibrations.
What’s the best course of action now?
Perhaps use an attachment method that allows vertical movement, but not horizontal? First thing off of my mind would be a loose-fitting dowel arrangement, with the dowels fixed into the carcase, and the torsion top set over them with loose-running holes. That would prevent movement of the table from twisting your top, but still keep it from sliding around on the legs.
Almost like a system of stilts? An issue I see with that is the holes drilled through the torsion box bottom. While it likely wouldn’t be an issue for years, that would be an opening through which moist or dry air could penetrate the box. Maybe it wouldn’t cause warping? But if possible, I’d rather leave the box caulked and sealed. Maybe I could make a sandbox type table and fill the bottom and side gaps between the table and the torsion box with sand?
Well, if you’re concerned about that, why not just add “hardpoints” to the bottom of the torsion box, then? Add MDF “pads” to the bottom of the torsion box, that have small counterbores drilled in them for the dowels to key into, without breaking into the torsion box itself? Just have the dowels stick up ~.250 from the carcase, and pockets .375ish deep into the pads? That way, no breaks in the box, no way for it to slide horizontally, and no possible force transfer from the table to the top?
I agree with @DanBrown: take a very simple route and treat it like you would a table top by giving room for seasonal movement. You can do it with dowels like Dan suggests (easier if the torsion box is already sealed up) or you can do it with simple brackets between the table frame and top, using screws and slots instead of dowels.
It isn’t sealed yet, and I do have quite a few scraps left over from the build. I think I’ll go with the pads and dowels. Thanks Dan