Perhaps it is a minor obsession of mine, but I love triangles – at least in structural elements. Take the cross section of a square, a circle and a triangle and guess what: the triangle is leaner.
Back in the day when I was task to design a carbon fiber equipment rack for a spy plane that was just too damn heavy, I took out the boring square aluminum tubing and replaced it with a tabbed triangular tubing, and then replaced the aluminum with carbon fiber and guess what: I took 60% of the weight out of those racks. My customer was pleased!
The RC-7 Crazy Hawk is still flying today at the DMZ in South Korea, and god only knows where else. Drones will not replace a team of highly specialized people risking their lives daily for a time!
So the DIY (do it yourself) X-Carve 3 axis “carver” is designed for folks that mostly want to carve out custom wood signs without having all the skills to do it the old fashioned way. It is great for that, and all kinds of DIY projects.
But we wanted more from the machine. We wanted to CNC machine our own MIC-6 aluminum molds! First we had to stiffen up the rails to take the “flex” out of the system. Our simple fix: bond in a unidirectional carbon fiber laminate to make the rails as stiff as a 12 year old boy’s – um, ah, never mind – very stiff anyway!
I created the mold models in Autodesk Inventor. Then we use Fusion 360 to generate the tool paths, and are experimenting with a number of post processors compatible with the Java based Chili Peppr, that communicates with the X-Carve.
Pictured is the dry run in wood of the matched matched-die mold we will attempt next in MIC-6 aluminum. The Series1 chair leg will be about four plies of a braided carbon fiber sleeve – similar to the braiding used for the fuselage frames in the Boeing 787 Dreamliner.
We will slide the dry fabric braiding onto a rubber tube, insert the tube assembly into the matched die mold and apply about 40 psi pressure to the tube. Then pull vacuum on the mold cavity and infuse a UV resistant epoxy resin via VARTM. If it works, we will have a sexy, lean and strong leg for our Series 1 Chair prototype. Wish us luck!
