Hmmmmm....I guess it depends on what you mean by "shut." I'm still game for the discussion because that was my original intention for posting....that Ted Hunt's description was not accurate and that most people combine other movements when they say they are only doing palmar flexion. No animosity here. I think we are using different definitions and different points of reference so its a learning oportunity for me. "Shut" could mean "closed" or it could mean "de-lofted" or a combination of the two. I'd say its both, but mostly de-lofting. I'll admit I could be wrong. Here is an experiment.
Build a model. Cut out a cardboard circle for the swing plane. Glue or tape a hinge flat to it at p6 out at the edge so one leaflet hangs off the disc. The hinge face pointing out from the cardboard plane represents the back of the left wrist at p6. The hanging leaflet is the left hand. Raising the loose leaflet is pure dorisflexion and lowering it is pure palmar flexion....pure hinge motions.
Now our goal at impact is to get the club face square to the target and to the path of club travel (the rim of the swing plane). Since by definition a weak grip is where the club face and back of the left hand/ left wrist are pointing in the same direction, this means we also have to find a way to get the back of the left wrist and hand to face the same direction the rim of the swing pane is pointing at impact ie the target.
Now, opening and closing the hinge by itself is a good representation of pure wrist palmar flexion and dorsiflexion. However there is no amount of hinging at P6 that will ever square the hinge faces to the club path indicated by the rim of the cardboard. As long as you ONLY hinge, the face representing the left wrist will always point perpendicular to the swing plane. The hinge face representing the back of the left hand can point a lot of directions depending on the amount of hinge, but facing along the club path to the ball is not one of them.
To achieve square at impact something else has to happen. We have to actually pick up the hinge and realign the pivot axis 90 degrees so it is square to the swing plane. In other words we have to ROTATE it counterclockwise until it stands on end. Palmar flexion only moves the hand on the wrist in a pure hinge motion. It does not alter the direction the hinge pivot axis points.
We want to rotate the left wrist pivot axis 90 degrees so the wrist and hand face the target and are square to the swing plane at impact. This requires an arm rotation, either supination, shoulder rotation or a combination. These motions close the club face significantly. If we look at the model again, the degree of palmar flexion at p6 doesn't really decrease the amount of rotation (closing) still needed to get square so we can say that palmar flexion is not really helping to close the club face in any practical sense.
Finally, you can do one more experiment. Place the hinge at impact position square to the the cardboard disc with the hinge faces pointing forward along the target line. Now play with the free leaflet of the hinge. No amount of hinging back (palmar flexion) will ever get the face pointing left at impact. In a weak grip the club face is aligned with that face. If you hinge enough into palmar flexion you can see that the face actually points down severely and right of target. It won't ever point left of target line unless you dorsiflex the hinge........ aka.....a FLIP.
Palmar flexion does give the look of a "shut" club face. However from the above does it actually close the face or just mostly de-loft it?