This page shows one way to attach the two major components of the cheiroballistra arms together. This method is probably not the same as what the cheiroballistra text intended, but it is very functional. Another useful method is to simply bend the bar around the hoop. For a more theoretical discussion have a look at the Cheiroballistra arms article.
Process step-by-step Edit
Attach the bar to a wise and file it's end flat, so that it can be bent easily around the end of the cone:
Now push the bar into the groove in the cone and attach both into a vise:
Bend the bar against the base of the cone:
Finally cut the bar at the center of the base of the cone. This keep the bar in place, yet reduces some mass from the arm.