Since Hogan gave us this wisdom, many golfing gurus and instructors adapted and modified his teachings on the swing plane; some did a good job and others not so good. Hank Haney states that the swing actually travels through several planes but that they are always parallel to the original plane, and this is a better description of what Hogan was trying to convey. I've written previously on the discussion of one-plane versus two-plane swings. This post is not about that or about the countless ways that the swing plane has been taught. Quite simply, this is about what helped me develop the feel of a consistent swing plane--one that I can repeat over and over again, regardless of which club I'm using. The swing plane is important; it allows one to hit the ball in powerful, repeatable, balanced manner with the ball arriving closer to its intended target.
The best way to experience a constant swing plane is to think of a modern day laser pointer. Actually, there are now training aids you can buy that feature a laser pointer on each end of a shaft. You could make one of these yourself with some electrical tape, two small laser pointers, and an old club or wooden dowell. However, you DON'T need this training aid to understand this timeless description of the swing plane. Martin Hall has used this laser technique and many other training aids (including stationary, angled PVC pipes) to illustrate a consistent swing plane. Most PGA professionals teach some form of this view of swing plane.
Instead of spending a bunch of money, use something you can utilize while on the course--your imagination. Imagine that each end of the club shaft you're using has a laser pointer on it. Forget the club head--think of a laser pointer coming from each end of the shaft itself--from the butt-end (handle) of the club and from the part that attaches to the club head. Yes, I know the club head hits the ball, but you see...you don't need to be exact--down to the milimeter--when it comes to working on your plane. If you're close to keeping parallel lines throughout the swing and close to keeping the radius of your swing always pointing at the line, the swing plane will repeat every time, so don't worry if the laser points an inch or so inside or outside the target line. Just get it close. If it's way outside or inside (especially when your arms are below the waist) then that can be a problem.
Set up in your address position using a neutral grip and good posture fundamentals. Align yourself parallel with the target or aim line; these two lines might be the same or different depending on your desired shot shape, but let's pretend we're going to hit a straight shot with perhaps a touch of draw, so the aim line and target line are the same. Remember that the target or aim line is imagined to be infinite, running forever in both directions.
Begin your takeaway (using a shoulder turn), keeping the club-end laser pointing at the target line for as long as possible (basically the radius of your swing circle). Eventually this will become impossible due to the fact that the shoulders must eventually turn to 90 degrees. At this point, the club will be roughly parallel to the target line and horizontal to the ground.
When you can no longer point the club-end laser down the target line because of the shoulder turn (and because the club shaft is horizontal and parallel to the target line), allow the wrists to hinge to 90 degrees (creating the L-shape between the club shaft and the left arm), such that butt-end laser now points at the target line. This will occur when the hands are just below or at waist level and just outside the right thigh; the left wrist should begin flattening (assuming a neutral grip). No additional wrist hinge is required after this; merely continue turning and raising the arms naturally to keep the laser on line. An important note: Once the arms are above waist level, it's permissible for the laser to point outside the target line, provided it still traces a line parallel to the original target line, but when you're not using a laser it's the feel of matching the target line that's imporant. If the laser points significantly outside the line when the arms are below the waist you'll be too flat and laid off; too inside and you'll be too steep.
As the shoulders continue turning to 90 degrees and the arms raise to the top of the backswing, the butt-end laser continues pointing down at the target line.
At the top of the swing, the butt-end laser may no longer point at (or parallel to) the target line but point directly away from the target, such that the club shaft is parallel to the target line (similar to how the club shaft looked when it was horizontal just below waist level). Likewise, the club-end laser would point at the target.
All that's needed now is to unwind into your downswing and followthrough. The body has a natural intelligence that will seek to retrace the backswing angles into the downswing. Practiced slowly, the lasers should retrace the target line on the downswing and followthrough, creating mirror images of the takeaway and backswing, culminating with a butt-end laser pointed targerward and parallel to the target line.
As with most golf teachings, there are detractors to this line of thought. Some say the exact plane depends on the golfer's physical characteristics, and that's true to some extent--especially above the waist. Bradley Hughes argues against the "pointing always at the target line" paradigm by discussing the variety of "off-plane" backswings among professional golfers whom always arrive at impact "on-plane," using a downswing plane that flattens out, and this is something I posted on earlier when discussing the "reversed loop swing." However, I'm not a professional golfer; anything I can do to make the swing simpler and more repeatable is preferrable. Almost all pros will retrace the club shaft angle closely on the downswing, however, with physical forces creating the deviations seen.
Pointing always at the line with the club shaft may not be a perfect or ideal plane, but it IS a steady, repeatable plane, and remember that the plane need not be exact or perfect. Just close in terms of retracing the target line and keeping as many parallel relationships as possible. Keeping either end of the club shaft pointing always at the target line on both sides of the swing is one way of experiencing a consistent plane, which will definitely help your golf shots if you've been experiencing multiple planes (especially an outside-in loop).
The golfer should move his body and arms in such a way that he can trace a straight plane line (that is along the ball-target line) with his right index finger and clubshaft during the backswing and downswing and early followthrough - when the hands are below waist level. The golfer should also consider the advisability of adopting a backswing style that minimises plane shifts as the hands get above waist level, so that it is easier for the golfer to get his clubshaft back to the correct clubshaft plane in the mid-late downswing when the clubshaft moves below waist level.