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I've not been able to find an electric sit/stand desk that is a size I want so I've designed my own. I'm confident in the electronics side of things but I'm not certain of the strength of the materials. The actuators I'm using have a stroke of 450mm and can push/pull 1500N so they're definitely strong enough but the desktop is 3.2m long with a simple rectangle steel frame made of 35mm square tube with a 2mm thickness. I will have a lot of gear on the desk so I want to be able to puch up to 100kg excluding the desk itself so I have to consider the weight of the materials used. Will this frame be strong enough to handle 50kg-ish in the very center without flexing?

Images of my design can be found here: https://i.stack.imgur.com/Rxx1Q.jpg

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  • It depends on the thickness of the steel tubbing.
    – Lee Sam
    May 28, 2018 at 19:56
  • It is 2mm thick. I did mention it in the post.
    – dotDone
    May 28, 2018 at 20:02
  • How solid is the top? If it is a bunch of planks fastened together that can flex at the joins, the horizontal tubes will be doing some work, and their strength might be relevant. If the top is rigid, it will really be supported by the uprights, which shouldn't be an issue. You can minimize the need to be concerned about the strength by ensuring that the top is rigid.
    – fixer1234
    May 28, 2018 at 21:18
  • That Redwood is going to flex. For that length and those forces, I'd want at least a couple more sets of legs in there, and some cross bracing. 35mmX2mm is none too big over that length, especially if you manage to get torquey with it. You might be alright as designed, but if I can't calculate, I always find it wiser to massively overdesign. Hit a hollow 2mm X 35mm rod with a hammer wrong, and you're liable to dent it. That could quickly lead to trouble.
    – Wayfaring Stranger
    Aug 4, 2018 at 19:39

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My structural tables don’t go “down” that low, but assuming A36 grade steel, (which is the most common in the U.S.), a 2 1/2” tube with a 1/4” wall thickness will support about 1,000 lbs. on a 10 foot span. Therefore, I’d assume two 35 mm tubes with 2 mm thick walls will “support” 100 kg without failing. However, I see several issues, 1) it will have significant deflection (flex, as you call it), 2) the legs are too small to keep the top from rotating, 3) 50 kg in the center of the top will depend more on the top than the frame, and 4) the joints act as “pin” connections without diagonal braces, so they’ll easily rotate.

BTW, are you sure the floor can support that much weight?

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  • Yes, floor is a big issue here. Is it actually flat, or will all be supported at just 3 or 4 points? Those spots will dent on you.
    – Wayfaring Stranger
    Aug 4, 2018 at 19:40

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