If you follow the line of the frame you will notice that the seat and back are able to move independently of one another. The radius at the feet is acting as the joint. The tension from that tight of a radius acts as a spring. This is in part to do with the material i used. The sides are made out of .25 x 2 inch 6061 aluminum. This alloy has a very good memory if it is bent cold. The sides are bent from one continuous stick of aluminum. The two ends join end to end with one weld right in the middle of where the seat is bolted on. After a little grinding and powdercoat there is no way to tell where it starts and where it ends. The sides were bent on a diacro , it was a feat to say the least. trying to get the piece back in to the bender after some of the last bends was virtually imposable. I can proudly say I got it right the first time not once but twice. The easiest thing in the world is to create something once, the hardest thing in the world is to match it identically.
The seat and back are made of .125 mild steel. They were hand bent with a jig I devised. I didn't have the money to have them rolled. The jig I created was two pieces of round bar(1.5" in dia.) welded about 2 inches apart. I then just slowly and tediously bent a little lengthwise and moved it through the two bars about an inch at a time. I had to be careful not to create facets. It had to be smooth. It worked very well.
Sorry I didn't document it well I didn't really have a good camera when i was making it. The good photos I have up here payed for so the chair could be in a catalog for The Furniture Society of America's conference. The catalog was about furniture prototyping. They wanted pieces that "could" be mas produced, they weren't making any promises though(bummer!).
Thanks for looking and enjoy.
A few people have inquired about a video showing how the chair rocks. Well here ya go.