The hub normal is coincident with the ‘Hub Axis’ which runs through the center of the hub. The term ‘Hub Axis Shift’ refers to moving a hub up or down its axis. The diagram below shows two struts meeting at the hub vertex. Postive values shift up the axis, negative value shift down the axis.
Set the hub axis shift value on the ‘Hubs’ tab of the ‘Struts and Hubs’ window. The animation below shows a hub axis shift of
-0.6 which moves the hubs toward the center of the sphere, and better aligns them with the strut intersections:
Setting a negative hub axis shift is more critical with low frequency spheres. As the frequency increases, the angular defect decreases, so a negative shift value should increase toward zero.
You can also shift the
DEST ends of the struts up and down the hub axis. This is done on the ‘Struts’ or ‘Spaceframe Struts’ tabs of the ‘Struts and Hubs’ window, and is documented in Strut and Hub Intersections Part 3 - Star & Ring flange Hubs.