If I asked you to swing a club with your lead hand only, you will move the club exactly on plane. You will do the same thing with your trial hand only. Swing Plane is a natural phenomenon.
The problem tends to occur when you put both hands on the club. For a number of various reasons including body position, wrist hinge and rotations, swinging the club on plane with both hands becomes increasingly difficult.
Moe’s instructions were to “Hit your positions”. He discussed this with me ad nauseum. Why was Moe so adamant? Because your positions determine your natural ability to move the body correctly – in order to move the club correctly on plane. Here are a few photos taken by Howie Alter.
Notice how the butt of the club is pointing at the ball. Also notice the tilt of his body. Pay attention to the trail arm folding and how the hands are hinging to support the club on the plane.
You can see in this picture how the club looks like an extension of the trail arm. The club face is parallel to the plane. Again, pay attention to the spine tilt particularly the right shoulder extension.
When a line is drawn from the backswing plane toward the ball, you can see how the club is referencing this plane throughout the motion. This is is the natural movement of the club “through space”. “Like a pendulum” was Moe’s description of this feeling.