Couldn't sleep (too much chili earlier) thought I share these thoughts.
Yoda is correct in saying the hossel and shaft rotate about the cg of the club head (not sweet spot). The discussion re. robots 10 pages ago had me thinking what was in question was the source... the cause, the raison d'être of the rotation (club face opening and closing). Do we all agree the hands (gears in the case of the robots) cause it? I hope so anyway...
Centripetal loading acting on the club head CG causes toe-down and forward deflection of the shaft as shown in the figure:
That centripetal loading (caused by centripetal acceleration not centrifugal) is reacted by the golfer's hands (primarily by the fatty palm area of the left hand in my opinion) at the butt of the grip. If we drew a line from the butt end of the grip to the CG of the club head, that is the axis of rotation that the torque (supplied by the golfer's hands) causes rotation about.
What I'm saying is the golfer CAUSES the rotation (about the "z" axis shown above) but it is the shaft and hossel that move the most (relative to that axis). They are farther away from it. Since the AXIS of rotation is through the CG of the club head (ON THE SWING PLANE) and the sweet spot in the face is close to that CG, it moves much less. The centripetal loading is similar to the second club shown on the link below. The axis of rotation is that dot-dash line.
Threaded Mode
