Some early hand-made prototypes using etched brass handles
I then worked through a lot of prototypes using 3/8" brass rod, trying out different lengths. One major hurdle was figuring out how to attach the wires to the handle. I knew the contact O would be held in place by the tension of the two wires, but soldering them to the handle meant the metal would lose it's spring-hard qualities. Crimping or crushing the wires into holes proved to be the best solution. It preserved the temper of the steel wire. But the thinness of the brass handle bothered me. It didn't feel very pencil-like. But if I made it out of 1/4" brass rod it proved to be too heavy. Aluminum ended up being a great solution because it is so light weight, but also a great conductor, and easy to design a crimped connection with the wires. It felt like the same size as a pencil, and only a little bit heavier.
Early handmade prototype O with steel wires
But aluminum's main problem (at least when you hold it in your hand) is that it can discolour, unless it is anodized. Anodizing involves immersing the aluminum in sulphuric acid while a current is put through it. Because the thin anodized layer is brittle, I had to anodize after the wires were held in place, which meant the wires had to be immersed in the acid. Stainless steel actually rusts in this situation, but titanium does not. Titanium can also be hardened, and it doesn't corrode, so that ended up being the perfect choice for the wires.
All that was left to do was find a way to make the contact O without soldering the tube hinges onto the O. At first I tried a lot of flat O's with tabs that could be bent, but the best resolution came through a combination of CAD and machine shop experiments that almost duplicated my early handmade ones.
Present oStylus model, 2011