My old assembly has served me faithfully for over 15 years. It was a torsion box, and dead flat. With the oil/beeswax finish it had glue popped right off. But it's really (really) showing it's age with gouges in the surface and some general wear and tear. Plus, I had made it roughly 50" square when I built it to fit the space available in the shop I was in at the time. It's moved twice since then, and my current shop can use a different size. So with all that stuff in mind I set out to replace it. The new one is exactly the same construction: 1/2" ply web, 3/4" MDF top skin, and 1/2" MDF bottom skin. Those choices were to keep the weight down as much as possible since I have to handle this thing by myself. There's 100 ways to build a torsion box and they are all correct...but here's how I did mine: First I need a flat base to put the top skin on, the web would then be glued down to it. So I jointed and planed some 2x stock to get them straight and shimmed them up on my sawhorses to be a flat plane. I used winding sticks to insure we had what we need, this wasn't level...but it was flat. First, this was what I had: (that screw rack is a freestanding thing).

Here's the base for construction of the new one: The members were glued down to keep them from shifting.

 

I'm building this upside down, so the top goes on the 2x stock. I cut it to size and squared, then cut the web pieces and the MDF side pieces. The web itself will be 3 1/4" deep.

 

I haven't seen other's do their web this way, but to me it makes assembly a lot easier. My web is all cross lapped (1/2 lapped?) and then laid on the skin for gluing....none of that toe nailing the multiple pieces in as is the more common approach. I gang cut the joints to ensure they all line up. This was a little harder on the long pieces, but not that big a deal. I spaced my cross members about 6" apart....I wish I had went with maybe 8". Anyway, the gang cut on the short members:

The lapped members go together easily:

and I wound up with this:

To get the web perfectly centered on the skin I glued the side pieces on and then the web. I was able to clamp it tightly around the edges, but for the center I placed a piece of sheet stock on it and about 200# of concrete blocks....not enough I was thinking but the best I could do. It seemed to work OK. After that glue was set I rechecked to ensure everything was still flat and then glued the bottom skin on (remember this thing is flipped upside down right now). For the bottom skin, I clamped around the edges, but I used 1/4" crown staples on the center ribs to tighter it down. I didn't do that for the top because I didn't want the holes to patch. The bottom skin was also not cut to correct size...I elected to have it slightly large and then flush trim it to size. Good thing the weather broke enough for me to do it outside. After that I simply put the side trim on (1" thick beech) and finished the trim with ARS, and my beeswax/oil mixture for the MDF. So now we have this roughly 3' x 6' table:

 

But now I'm stopped. I need to build the base and won';t be able to go get some things I need until this covid thing breaks. My old table simply sit on some plywood uprights, but I'll have a couple of cabinets with drawers for this one (maybe). My new top is still a lot heavier than I expected, at least 200# +, I can lift it with a hydraulic table and then stand it on end until I get the new base built.

That's a nice build. Last a lifetime!!!

Nicely done and plenty big too.  I like it!

Very nicely done.  I also have a torsion box assembly table.  Like yours, when it is flat you can reference off of it.  If I were to build another one, I would some how, have cut-outs to allow for clamps to clamp down in the middle of the table.  Be safe.  Danl

That is one substantial build. I don't do that much flat work so if I had a table like that it would have to break down.

Man, I Love It!

 

Wish I had some room for something like that. Right now my assembly table is a lazy susan affair that sets on 2 saw horses. I've been thinking about replacing the single 3/4" piece, plywood top with an interior type house door. No way could I handle a 200# unit. I have to move it to storage when not actually using it.