I have found during my teaching career that students have many misconceptions as to how to swing the club. One of the most frequent misunderstood concepts is the rotation of the clubface during the swing.
It is true the clubface opens in the backswing and closes in the follow through. The confusion comes in how this is interpreted. The opening and closing of the clubface is relative to the target line rather than a rolling of the hands around the circumference of the shaft.
Try this simple exercise to understand the correct motion. Take an iron and hold it straight out in front of you with the toe pointing straight up. The clubface is now pointing directly toward your target. Now rotate your body around your spine slightly to the right so the club has moved about two feet from its starting point. Do this without any rolling of the hands so that the toe is still pointing straight up. Notice how the clubface is now pointing right of the target line. At this point the clubface appears to have opened. Do the same exercise except this time rotate your body slightly to the left so the club again has moved about two feet. Notice how the clubface is now pointing to the left of the target line. At this point the clubface appears to have closed.
During the swing the clubface remains square to the arc. The opening and closing refers to the clubface and the target line. If you roll you hands clockwise during the backswing you must roll them back the exact amount in order to square the clubface. It is nearly impossible to do this with any amount of consistency.
Here is a simple drill to help demonstrate the correct motion. Grip your putter with the flat part of the grip facing up - while making three quarter swings make sure the flat part of the putter grip is always facing towards you. After doing this with your putter take a short iron and create the same motion. You'll soon be hitting straighter and more consistent shots.