[no_mind_golfer]

nm golfer - you wrote with respect to my diagram.

I disagree strongly with your depiction of events. During the release swivel phase and HH action phase of the swing, the different club parts are not rotating about the imaginary axis between the grip and the CG of the clubhead. What is happening is that the imaginary axis is moving in space due to movement of the flat left wrist/hand in space. The movement of the flat left wrist/hand occurs along a circular arc (relative to an imaginary center of the circle situated "somewhere" within space and all those parts (toe of the club, sweetspot of the club, hosel of the club) have the same angular velocity as the rotating flat left wrist/hand relative to the center of the imaginary circle. In other words, any point on that imaginary axis between the grip and the CG of the clubhead has the same angular velocity as the hosel and toe of the club - with respect to the instantaneous center of the imaginary circle of the flat left wrist/hand's rotational arc. The key point is "instantaneous" - if the flat left wrist/hand suddenly rotates along a tighter curve, then there must instantaneously be a different imaginary circle of rotation for all the rotating units (left hand, hosel, sweetspot, toe of the clubhead) which always have the same angular velocity relative to the center of that instantaeous imaginary circle of rotation. The only time that this system will breakdown is if the left wrist suddenly bends and doesn't remain flat.

Jeff.

Nothing imaginary about it.

Sorry Jeff but...

(Now that I think I understand what is being argued here ...) I have to agree with Yoda and (probably Yodaslurk earlier) position(s). The physics cause the CG (call it sweet spot if you must) to remain stationary as the club twists about the Z axis (in MY diagram above). The CG is on the line of action of the centripetal acceleration.

Centripetal acceleration is a fact of life.... Its line of action (through the c.g. on the (instantaneous) plane of the golf swing, is the axis of rotation the club parts move about as a result of the golfer's hand torque.

Sometimes thing are best proven to one's self by experiment.

-Take a carpenter's square or some such thing.
-Tie a string to one end and the other end of the string to a door knob or something fixed.
-Take a bungee cord and attach one end of it to the middle (CG... sweet spot etc.) of the other leg of the carpenter's square.
-Have your assistant pull back on the bungee to simulate centripetal loading.

Now you give the thing a little twist. Observe ... what axis is it rotating about? That's right... the line of action of the bungee.. ie line of action of centripetal acceleration (less any adverse effects on the experiment due to gravity).

The club operates identical to this example in 3D.