Will a Torsion Box Flex?

I think the answer depends on how strong you make the torsion box and how heavily loaded it is. All structures have a max usable rating.

If the load is high enough, it will bend until it sits flat with your bench, but you can easily shim it to your bench while unloaded.

Alternatively you can make a three legged base for it, It’ll always stay flat then 8^)

As dschlic1 said, if you build it strong enough it won’t flex. However, how to determine what is needed to make it strong enough is the question. What is beautiful about a torsion box is that the distance between the skins largely determines how stiff and strong it is. The internal members are really just spacers to hold the skins apart. They can be relatively light. Because of this, the torsion box can be large and light, but still be stiff and strong. However, if you want to be precise and maximize the strength and minimize the weight, you will need to either do some experimentation or find someone who knows how to do some calculations.

For example, look at a typical hollow core door. They are usually very light yet quiet stiff and strong. Tear one apart and you will find very thin skins (maybe 1/8” or less) and the interior grid is very thin and light pieces that may not even be well attached to one another. I have seen some that are nothing but corrugated cardboard in a snake pattern edge glued to the skins. Still pretty strong.

Actually, your entire bench or table can be built like a torsion box and you won’t need a separate one for the base. Build it with a typical top, a continuous shelf (full length and width) underneath, four sturdy legs, panels on the sides or suitable cross bracing, and you have a torsion box. You can make it as stiff as you like.

Hmm, Now you are asking if perfectly flat torsion box table will stay flat as you move it around?

Better Question:
‘How does a perfectly flat work table sit on the uneven floor?’

Even a relatively flat garage floor needs work table legs to have adjust-ability, for those times when one leg is not touching the ground. When permanently located, a wood shim is the simple solution. When need a mobile solution, use ‘leveling feet’ or ‘leveling castors’ to keep the table from rocking on an uneven floor.

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, Doom, despair, agony on me… - Albert King - Born Under a Bad Sign released 1967

Better Question: How does a perfectly flat work table sit on the uneven floor?

- CaptainKlutz

I agree this is a better question for this example. If the floor dips, and the top tries to stay flat it may not flex, but a corner will certainly dip. That in turn will create a flex of sorts.

-- Think safe, be safe

I have used corrugated cardboard, made for torsion boxes, several times with great success. You get a absolutely consistent size of the cross-members and a ton of glue lines.

Weight is your friend. A heavy bench won’t move around when you are planning a piece of wood. Remember torsion box construction is designed for light weight besides stability. The top can be quite thin and susceptible to puncture, so heavy hammering on a torsion box surface can wreck it. Torsion box construction is usually used in the assembly stage of products to ensure everything goes together plumb and square. In metal working circles it’s known as a surface plate.

The mdf torsion tables I’ve made were very heavy. They definitely will sag if not supported.
One odd thing that happens the bottom face always come out flatter then the top side.
I stopped use a torsion table because of space. I will make a grid style assembly area if I’m building a door or something with miters and frame.
Good Luck

-- Aj

Everything flexes more or less.
the rigidity depends especially of the height(thickness) of the box.
One can not ensure it will not flex while rolling. It will also depend of the masses you would put on it and their distribution.
Use leveling feet when stationary.

As one knows, a torsion box must have two skins to resist to torsion as this shoe box experiment demonstrates:

-- Sylvain, Brussels, Belgium, Europe - The more I learn, the more there is to learn (and that is nice)

It will not flex unloaded. The wood structure can flex or fail loaded on an uneven surface, but you will likely always have three wheels on the ground. I would not over think it. Build it, use it. If you move it to a new location and plan to put a lot of weight on it, shim the low wheel.

I make torsion box bases out of 3/4” MDF for all my mobile bases. The largest was 22” x 66” and they are plenty stiff. I don’t notch the ribs, I make the center ribs in the longest dimension full-length, and cut the rest to fit. I dado/rabbet all the ribs 1/4” into the skins. Glue and brad nails to fasten. On my shop floor I typically have one caster off the ground; I shim it as necessary.

Ian Kirby designed a bench with a torsion box top to double as a veneer press. It apparently stayed flat enough for pressing.

Everything flexes more or less.
the rigidity depends especially of the height(thickness) of the box.
One can not ensure it will not flex while rolling. It will also depend of the masses you would put on it and their distribution.
Use leveling feet when stationary.

As one knows, a torsion box must have two skins to resist to torsion as this shoe box experiment demonstrates:

- Sylvain

-- Steven.......Random Orbital Nailer

I would use retractable rollers and then add levelers for the legs to deal with uneven floor and wide aprons to help with sagging and that will help prevent flexing or sagging even with heavy loads. Put a heavy weight on each leg and use some winding sticks to help adjust the corners to get any flex out of it.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.