Ki is a stool that can be assembled and disassembled without tools. For street food vendors who pack up their chairs and tables every night.
Material ConneXion is a library of material samples. I visited the one in Bangkok to discover new materials. It is an incredible source of inspiration, definitely worth a visit. No photos are aloud in the library. I spent several hours in there with a notebook. One sample there is Wood-skin. A nylon fabric laminated to thin plywood with channels routed into it to make living hinges. the Material Connexion codes are MC 7155-01 and MC 7155-02. This looked like a great material to use for Ki.
before chosing the middle one. Hand sketching with felt tip pen and copic marker.
refined it, sweat the details. Hand sketching with felt tip pen and copic marker.
Sketches alone don't explain concepts to other people. A quick scale model is much more effective. I could show (not tell) people exactly how the legs pierce the wood. A scalpel, some balsa wood, blue card and some plastic extrusion from Eckersleys, was all I needed to demonstrate my concept.
What glue with which fabric? The glue used on the swatch I saw at Material Connexion is a trade secret. I could have spent along time researching it online. But in this case it was quicker and more accurate to try it myself. So I tested four glues on three different fabrics. The glues were: PVA, polyethylene, spray contact and brush contact. PVA on denim won outright.
I used an electric router (not cnc) to test if routing could be done after laminating the fabric to the timber. It worked, even with a V-grove bit that was too small. It was quicker to test this with a non-CNC router than program a CNC router. There was also a risk that the glue might destroy the bit - thankfully it didn't.
I tried cotton, denim and 5mm wool felt. Felt would make the stool very comfortable, but it was too thick. The thickness caused the sides to not lay flat when folded over. This was critical to flat packing. Denim had the best all round property of strength, aesthetics and minimal thickness.
I spend half a day in Solidworks figuring out how to make the perfect bayonet mount for the legs. after hours of modeling, the bayonet was almost done, well usable. I looked over at power outlet next to my computer. It hit me. I should use a friction fit to hold the legs in. A plastic socket attached to the stool would meant that I didn't have to make a mating part to attach to the leg. The steel legs could be just a 90 degree cut.
I needed to test the friction fit leg sockets. So I FDM 3d printed some to join steel tubes to the plywood seat. The first one was made for some 50mm aluminum tube that was laying around. It joins the tube at 90 deg. The tolerances where acceptable on this first one, proving that a friction fit socket would be strong enough to hold the legs to the stool. The legs enter the stool at a 10 degree angle, so when you sit on the chair your weight forces the timber to tighten around the steel legs.
I redesigned the legs socket as a friction fit. It took a fraction of the time to design it in Solidworks because I had already tested the design. Lessons learned - don't design as you go in Solidworks. It is time consuming.
Ki was drawn up in 3d CAD. This time I used solidworks. Then I made 2d drawings and printed them as a reference when making Ki. I also used them to talk to the CNC programmer and other technicians in the university workshop.
I made a working prototype out of ply wood and denim. The steel legs were powder coated. It supports the weight of two people.