Tugendhat  

I have seen leaf springs... I have seen leaf springs being annealed they use oil to cool the leaves then they are shot peened to relieve any stress

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I don't think the steel is sprung, that would preclude welding wouldn't it? I'm not an expert but I'll ask someone who is.
I did find out the dimensions and grade of steel used, but I forget now. Diligent googling with show it up, I think for stainless it is just plain old 312 or 316

The reason I ask is...
I've ...
The reason I ask is...
I've managed to piece together enough information to draw up full scale plans to make one. Only problem is making the frame may be a little beyond my ability. I can weld the pieces together easily enough, but bending the steel might require equipment far beyond my pocket.

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not necessarily if you can find a small metal workshop, my father rolls steel bar and its actually really fast. Just pass one length of bar through the rollers until you get the desired curve and then repeat. Bending those sharp corners though I know little about.
If I were you I would not show the manufacturer the pictures or plans, just take in full scale drawings of individual parts,maybe getting enough made for 3 or 4 chairs might bring the cost down a little overall.
Good luck with it, I would LOVE to see pictures.
ps there is allways a small (6" or so) flat area at the end of each arc that might have to get partially or fully cut off, but you probabaly knew that, not really a problem with this chair though. But the big arc on the seat might be done in a hydraulic press...
I don't think its sprung at all, though I could be wrong, Koen will know.