[O.B.Left]

But 2-C-1, Swingers Hinging says, in essence, that for maximum compression, the clubface must rotate around the same center as the shaft during the interval. I am looking for clarification of this.

For theoretical total compression the point of contact between ball and face must remain connected ( Homer said "as if welded together") during the impact interval. No "wobble" so to speak.

But for lofted clubs the ball will roll on the face to varying degrees as you mention. Which Homer assumes to be the case in 2-C-1. Wobble or leakage due to loft. That slightly glancing blow due to loft aside to maintain the point of contact between ball and face throughout the interval requires a uniform motion or arc. Meaning that the angled clubshaft and the closing clubface are both rotating around the same center. At the same rate.

Horizontal Hinging , closing only with no layback does not add loft dynamically during the impact interval , which would deaden the blow , compression leakage. Something that can be used intentionally to great effect on short shots but is the hackers floating tee ball shot. Normally the result of "Steering" the clubface square to the hole in a misguided attempt to add a linear, inline , square to square blow to a ball that should be hit with an arcing clubhead and a closing face.

I must admit to not being able to draw the clubfaces center for vertical hinging. I go all foggy on that bit of business. Homer did these drawings however.......I wish they'd made the book. Words do fail when describing geometry. Angled Hinging it is said , has no center for the clubfaces motion......

Maybe Lynn could explain or draw it out some day.