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Will a Torsion Box Flex?

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Forum topic by wilschroter posted 01-17-2022 05:21 PM 674 views 0 times favorited 14 replies Add to Favorites Watch
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wilschroter

209 posts in 1984 days


01-17-2022 05:21 PM

In a previous post, I asked about creating a dead flat surface for my new workbench and I was thankfully turned on to the Torsion Box concept.

Would a Torsion Box concept work somewhat effectively for the base of my ROLLING workbench as well, helping prevent some of the flex that would naturally occur as the wheels are on slightly different heights in the shop? I’m a little concerned about the flex transferring to the rest of the workbench, including the work surface. I like the idea of the Torsion Box because it seems to offer a lot of rigidity without a ton of weight.

To be clear, I may end up with one on the top and one of the bottom, but right now I’m just asking about the bottom.


14 replies so far

View dschlic1's profile

dschlic1

517 posts in 3429 days


#1 posted 01-17-2022 06:37 PM

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.

View splintergroup's profile

splintergroup

6950 posts in 2682 days


#2 posted 01-17-2022 08:50 PM

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^)

View bilyo's profile

bilyo

1550 posts in 2562 days


#3 posted 01-17-2022 09:10 PM

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.

View CaptainKlutz's profile

CaptainKlutz

5613 posts in 2954 days


#4 posted 01-17-2022 10:37 PM

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

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therealSteveN

9992 posts in 2033 days


#5 posted 01-17-2022 10:48 PM


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

View HowardAppel's profile

HowardAppel

160 posts in 4493 days


#6 posted 01-17-2022 10:57 PM

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.

View MrRon's profile

MrRon

6321 posts in 4703 days


#7 posted 01-18-2022 12:08 AM

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.

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Aj2

4455 posts in 3257 days


#8 posted 01-18-2022 01:26 AM

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

View Sylvain's profile

Sylvain

1675 posts in 3959 days


#9 posted 01-18-2022 08:59 AM

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)

View BlueRidgeDog's profile

BlueRidgeDog

918 posts in 1239 days


#10 posted 01-18-2022 02:28 PM

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.

View yamato72's profile

yamato72

53 posts in 415 days


#11 posted 01-18-2022 06:19 PM

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.

View Loren's profile (online now)

Loren

11506 posts in 5107 days


#12 posted 01-18-2022 07:12 PM

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

View Dark_Lightning's profile

Dark_Lightning

5097 posts in 4568 days


#13 posted 01-19-2022 01:52 AM



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


Yup. EVERYTHING flexes, it’s just a matter of how much.

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

View Lazyman's profile

Lazyman

9602 posts in 2847 days


#14 posted 01-19-2022 02:03 AM

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.

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