What Material Should I Use?

HI

I am designing a chair. As I have gotten into it I am learning about materials and processes.
Attached is a picture. This is not my chair but the idea is the same as far as the way the stand works.
I was wondering if someone could give suggestions on what materials would be best for a chair like this?
My chair currently shakes and is not as strong enough.

Would 316 stainless steel rods - 12mm work?

Thanks

Would 316 stainless steel rods - 12mm work?

Hmm, 12mm Stainless sounds a bit over kill, heavy and quite expensive…you might be able to get away with something thinner. Pop to your local furniture store and take your callipers measure the dia and speak to a wire former to get some more specific advice. You might need a cross brace to stop the side to side wobble instead like these ones:

hi
i have tried the cross bar. it is better but it still shakes.

my chair is much bigger than those you posted.

those chairs you posted are 11-12mm dia.

i think it has to deal with the material make up of the rods.

i wonder why it works for the example i posted?

There’s a bit more to it than material thickness. You need some triangulation somewhere if you want to get rid of the side to side shake. Why not post a sketch of what you’re actually doing, that would help us help you a bit more.

As NURB points out, triangles are a must-have.

It’s an easy experiment to do to learn the concept. Take three sticks and strew them together to make a triangle (A). Take four sticks and screw them together at the ends to make a square (B). Now clamp down the four sided piece and apply a side-load (C); it will easily rack out of “square”. Do the same with the three-sided piece; you will notice that it does not deform. It can’t, because to do so would require that one of the three legs change length. The square (D) could be made strong enough to not deform, but it would require either additional material in the form of gussets, much heavier tube/rod to take the strain (torque), or a “cross brace” (D). The joint can be mechanically fastened, welded, glued, etc., but the result will be the same.

I am betting that the example that you posted would be VERY shaky also, and the span (the distance between) the front and back vertical support (legs?) leads me to believe that it would sag in the middle.

Only one of the red diagonal braces would be required on the ends, but two looks better.

You might want to consider building some scale models of your design to test their strength; tooth picks and 1/8" x 1/8" balsa wood are great tools testing structure.

Funny! I was going to suggest the toothpick bridge game, too!

Funny! I was going to suggest the toothpick bridge game, too!

Toooooo much fun, huh? As a kid I spent hours, and a couple of metric tons of tooth picks, building bridges, towers, buildings and the like, and actually self-taught myself a lot about “structure” with out even knowing it. Too bad “super-glue” was not around back then (196something), it took hours for that old Elmer’s Glue to harden; I consequently learned the concept of “jigs and fixtures” at around eight years old (wax paper, pins, and celotex insulation board).

For toothpick lovers, check out this guy:

http://www.toothpickcity.com/

There’s a saying where I come from, “If in doubt, truss it out”.