The hub plane is specified by the hub vertex and the hub normal, ie the hub plane is at right angles to the hub normal and coincident with the hub vertex:
By default, the hub plane bisects the hub along its width so that half the hub depth is above the plane and half the hub depth below it.
Unfolding Struts onto Hub Plane
Unfolding struts onto the hub plane. Method: for each strut at the hub, get a vector perpendicular to the hub normal and strut. Rotate the strut around the perpendicular vector by angle delta so that it is coincident with the hub plane. (delta = angle between hub normal and strut - 90°). The “unfolded” angle beta2 is greater than beta.
A Hub cut from sheet metal. This simple method is sometimes used to join wooden struts. To construct a hub of this type, the struts must be “unfolded” onto the hub plane. Imagine the struts “folding outward” to meet this plane. This will give the required cutting angles. Once the hub is cut, the arms are folded back to coincide with the struts.