Last year, I designed and built a series of six chairs from road signs, all nearly identical. The chair shells were folded aluminum signs and the bases were made from good 'ol Alabama pecan wood, milled, sanded, and lacquered within an inch of their life. They turned out pretty well. I wrote an article about them, got paid, and enjoyed them for about a week. Then, one day after work, I sat down in one of them, and the two joints in the back legs blew out. The chair collapsed. I smacked my elbow and my head pretty hard on the way to the floor.
Time passed. The rest of the chairs seemed fine, more or less; the broken one had a flawed joint in the back, which gave way once my weight was leaned back into the seat. However, I was nervous every time I sat in one from there on out, and especially nervous that someone else, perhaps bigger than me, might sit in one and break it. I'm fine with breaking my own creations, but the paranoia and anxiety and embarrassment around the idea of someone else possibly injuring themselves and thinking I was a moron was almost too much to handle.
I had broken a cardinal rule of design -- putting form above function. In my desire to have a sleek, light form, I had ignored some structural considerations. The back legs were extremely slanted -- over 20 degrees. That joint, where the cross-piece intersected, bit too deeply into those back legs, weakening the wood there. The legs splayed in only one axis -- front-to-back -- which made the chair unstable side-to-side. The stock for the legs, at 1" square, was not strong enough to resist the twist and tension in the folded aluminum signs, which meant the legs didn't all hit the ground evenly once the base was bolted to the sign. The 3/4" dowels I used as cross pieces were also not strong enough to resist side-to-side motion. The base was essentially a series of parallelograms, with no triangulation, which led to a lack of stiffness.
Time passed. The rest of the chairs seemed fine, more or less; the broken one had a flawed joint in the back, which gave way once my weight was leaned back into the seat. However, I was nervous every time I sat in one from there on out, and especially nervous that someone else, perhaps bigger than me, might sit in one and break it. I'm fine with breaking my own creations, but the paranoia and anxiety and embarrassment around the idea of someone else possibly injuring themselves and thinking I was a moron was almost too much to handle.
I had broken a cardinal rule of design -- putting form above function. In my desire to have a sleek, light form, I had ignored some structural considerations. The back legs were extremely slanted -- over 20 degrees. That joint, where the cross-piece intersected, bit too deeply into those back legs, weakening the wood there. The legs splayed in only one axis -- front-to-back -- which made the chair unstable side-to-side. The stock for the legs, at 1" square, was not strong enough to resist the twist and tension in the folded aluminum signs, which meant the legs didn't all hit the ground evenly once the base was bolted to the sign. The 3/4" dowels I used as cross pieces were also not strong enough to resist side-to-side motion. The base was essentially a series of parallelograms, with no triangulation, which led to a lack of stiffness.
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| The original chairs, pretty as you please. |
