[Yoda]

If you are tempted to answer that the hosel leaves the clubshaft plane in order to rotate around the sweetspot post-impact, then look at the following Martin Hall swing video.

Note that he is using a simulated golf club that has very long clubhead (>12" in length). If that club has the same club lie angle as a regular club, then doesn't Martin have to swing the club along the same clubshaft inclined plane (along the surface of that plane board) even though the sweetspot plane angle in this example is going to be very different to the clubshaft plane angle. Then, in what sense do you imagine the hosel rotating around the sweetspot of that clubhead post-impact? Also, in what sense do you imagine the clubshaft rotating onto the sweetspot plane of that club post-impact?

No, Jeff, he does not "have to swing the club . . . (along the surface of that plane board)". In fact, he must not. That is the whole point of this discussion, and it is exactly the piece of the puzzle you are missing. The Sweetspot always orbits on the Sweetspot Plane whereas the Clubshaft moves to and from that Plane. In so doing, it moves from and to its own Clubshaft Impact Plane.

Look, this is not that hard. Because the Sweetspot is 'outside' the Clubshaft, and because they are aligned on essentially the same Plane throughout most of the Golf Stroke, then either the Clubshaft must have rotated to the Sweetspot Plane or the Sweetspot must have rotated to the Clubshaft Plane. There are no other alternatives.

When you demand -- in either Martin's demonstrations or your own -- that the Clubshaft adhere to the Plane Board (except during Impact), you also demand that the Sweetspot leave its Sweetspot Plane and go the Clubshaft Plane. In other words, you insist that the Sweetspot rotate off its own Plane and onto the Plane of the Clubshaft (as made visible by the Plane Board). And that wobbly motion, sir, just ain't the way it works.

The Plane Board is a useful and practical theoretical conception. But, the truth is that if the Shaft stays on it throughout the Stroke, you will necessarily disrupt the Sweetspot's orbit. And that particular malfunction has a name . . .

Steering.