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I'm wondering if it's possible to create a high one legged 1.5 meter wide bench using 3/4 or 1 inch iron pipes (and fittings) with 3 or 4 mm thick walls. Basically, I want to have one continuous pipe unconnected at both ends. One end is behind the backboard and the other is underneath the footrest.

As you can see in the attached picture, I created a model out of wire and paper to help me better visualize it. It has a back, a seat, and a footrest.

It should support the weight of 3 adults. I'm afraid that the leg will have too much weight and one of the corners will fail. Would different diameter/thickness help achieve this simple design?

Feedback is much needed

Cheers

Edit 1: Added a side view picture of the model. As shown, the one leg is also tilted forward. This only makes thing worse. I'm starting to doubt the viability of this idea as is.

enter image description here

enter image description here

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  • So you expect a 1" pipe 90 degree elbow to support 250kg? No chance. I have taken a pipe elbow with 18" legs and bent it just with my hands...
    – Solar Mike
    Commented Sep 24, 2022 at 11:17
  • Think most decent size pipe will bend with weight without supports(more legs). Maybe solid 2 inch might hold the weight.
    – crip659
    Commented Sep 24, 2022 at 11:19
  • You need to deal with levers. One thin person at 150 lbs at a distance of 5 feet will give 750 ft/lbs downward force.
    – crip659
    Commented Sep 24, 2022 at 11:42
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    @crip659 Solid adds very little .vs. tubing, but larger tubing adds a great deal .vs. smaller tubing.
    – Ecnerwal
    Commented Sep 24, 2022 at 13:28
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    There is no need for titanium here. Plain old steel or chromoly will do fine, in the right dimensions. Find some mechanical engineering class in need of a homework assignment...
    – Ecnerwal
    Commented Sep 24, 2022 at 22:45

2 Answers 2

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With appropriate tubing (not pipe, there's a difference) this could be done. What material, size and wall thickness the tubing is would be up to you (or your mechanical engineer) to figure out. I'd guess 2.5-3" might be needed, rather than 1" Heat treatment may also be a factor.

There are early 20th century classic steel tubing chair designs done pretty much this way. Doing a bench will definitely need beefier tubing, due to the longer levers and higher overall forces.

Cesca chair image from Knoll no endorsement implied

If trying to use threaded pipe and fittings, 4" would be a guess at a possible starting point (formed bent tube is much stronger than pipe fittings.)

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  • So that chair, one person ie 120kg max... so bench for 3 at 120 each is 360kg...
    – Solar Mike
    Commented Sep 24, 2022 at 13:50
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    Which (along with longer lever arm and not using paired supports) is why much larger tubing is going to be required. And 120kg max is probably not a safe bet as a chair manufacturer.
    – Ecnerwal
    Commented Sep 24, 2022 at 13:53
  • Ahh, 120kg may be an average in some countries...
    – Solar Mike
    Commented Sep 24, 2022 at 13:54
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    Can't safely design for average. Gotta go for 95th percentile at least, and then you can get into the warning labels they don't look at before they sit down.
    – Ecnerwal
    Commented Sep 24, 2022 at 13:58
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One inch carbon steel bar will probably work for this, but may still be a little flexible. Take a detailed drawing of the shape ypu want to a place that bends reinforcing steel (which is carbon steel). unless you have a press than can bend it yourself.

The drawing will also help you determine what length you need, feels like about 10m = 30 feet which is available, but not at big-box hardware, and kind of hard to transport (unbent) with a light vehicle.

Pipe will almost certainly be too flexable in 1". but 2" could work. although those bends may be too sharp for 2" tube.

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