I have remade the centering arm. The goal was to make the design simpler so that somebody would need less tools time and money to build their own.
I have also address the dipping problem that is present with the arm. I open a small hole with my hands and place the oner in afterwards to bring the bottom to size. with some practice, this will only add a second or to to the time that it takes to make a piece. I have also thought about the philosophy behind the arm a little and will add those thoughts to the centering arm section. I hope to get some plans of the arm up on the site in a month or two.