Main shaft held in bearing as in helicopter. Head measured with dial gauge. Dial gauge shows extreme wobble in head, but shaft is straight. Hole through head is not parallel with axis of head. Eccentricity is more than 1MM at head. More at ends of blade-grips. Even more end of rotor blade, eccentricity is very large! Helicopter shakes badly when blades are spinning. Got on the myford ML7, and using vertical slide, and dividing head, made a new one from a cylindrical aluminium billet!