I could be wrong, but I don't think 1L is the chapter in the book I would use to compare components. 1L covers the basic geometry. I think it's difficult to use 1L to explain things like shoulder, feet, knee, and hip components. I think you may be painting yourself into a corner by not looking further in this discussion...

1-L and "10-13-C"
 

When I see "Rotated" I think 10-13-C which is, turn around the spine or could be turn about a post.
I see little use but it is possible and would be 1-L. this would not be on a practical plane for full swings.

The original question on FLAT and Rotated BS planes ( where the rotated plane may be too steep) I would answer is because it intercepts a starting point for a practical DS plane.

Most think this to be the TSP. I think of TSP as being a point-any point- from which a practical DS plane can be constructed.

Not that I really want to get into this here but--
Trying to create a machine that represents all elements of the golf stroke is difficult. Most attempts have resorted to the "Double Pendulum" model. In my simple mind- NOT GOOD. I have been thinking along the lines of HAND PATH GEOMETRY and single pendulum. And if the hand path geometry can be expressed as a mathematically determined figure the computer (real computer) is "home free.
So, I started thinking as the Hand Path Model being Hyperboloid of single sheet and the club is simple pendulum
.:scratch: :hello2: :clap: :dontknow:

HB

Yeah, I agree with that, Kev. Specially when it doesnt have shoulders, feet, knees or hips. Its a model which reveals the geometry inherent in a sport when using an instrument like a golf club , with its hooked face and inclined lie angle. The geometry of a Hinge Action of an Angular (circular) Motion on an Inclined Plane. ......I think itd work for a hockey stick stick or shot too. Got to think on that one a bit.....wheres my book?

I think its another definition thing again. To get Homer you gotta get his point of view I believe, his perspective , eye ball wise. DTL, caddy, players view etc. D sorted me out on one of these a couple of months ago as I recall. Its easy to get things mixed up. Homer can also, in words, shift his visual point of view quickly. Angle of Attack, Arc of Approach......different points of view of the same clubhead path. Confusing but very necessary.


"At right angles to the spine" here to me implying looking DTL at a golfer, who given waste bend will show his shoulders describing a motion which is at right angles to his spine but tilted forward vis a vis the ground. Like Mr Woods in that photo above say.

Shoulder Turn
 

I am comfortable with HK's view. This should be easy geometry. The component- Shoulder turn, The variations- HK illustrates 5,
lets reduce it to 3. We place a disk centered at the golfers axis of rotation. put a point on the circumferance of the disk.

#1 the axis and disk are not rotated- Varation ZERO
#2 The disk and axis are rotated such that the disk plane is always perpendicular to the axis of rotation- variation ROTATED
#3 The disk plane is not perpendicular to the axis and therefore the disk will appear to "wobble" on the axis as the disk and axis are rotated. This is the variation that exists for "flat" backstroke and "on plane" downstroke or other planes that dont meet #1 or #2.
There is more geometry. If, the DS plane Top is not precisely located for a proper "wobble" the golfer can not obtain/maintain a straight plane line without compensations. This "wobble is set BOTH by amount of backstroke rotation and axis tilt at/near the top.

Just my opinion-All disclaimers apply

Ps. Which leads to the question - Should the shoulder be on a downstroke plane to the plane line or to support the hands?

HB

Interesting analysis.

Personally, I am trying to go to a bit steeper shoulder turn to help get my mid-section out of the way. With a bit flatter shoulder turn I tend to be a herdsman (humper of the goat).

Standard Shoulder Turn....Flat Back/On Plane combo. One great description of this was from Ted Fort (aka Yoda's Luke) . Imagine your Right Shoulder being a paint brush that paints a "7" in the air......flat back and then down the plane, diagonally. Like a 7 when you look back at what your shoulder is painting. If you know what I mean. So its not describing the same motion back and down, two different motions, directionally. Its a bit counter intuitive I know, but its a bit of genius, cant tell you how much this has helped me. And upon investigation we do this sort of thing all day long, doing all sorts of motions. We direct our Hands and the Pivot responds.

To answer the question in your P.S. The Right Shoulder can only go down the Inclined Plane if its on the Inclined Plane at Top to begin with. Making for a TSP plane angle by definition, a Plane ( from Hands to Base Line) that also runs through the Turned Right Shoulder at Top. So the Right Shoulder is doing both ......down plane motion and supporting, directly pulling the Hands in Startdown. Made necessary by the Downstroke Sequence where you let your Pivot pull the inert Hands, Arms in Startdown. Since your Pivot (right shoulder) is pulling it best be pulling somewhere, ideally at the Plane LIne given that the Hands are going to follow it directly , linearly.

If I had a scanner down here (im on vacation) id do some drawings . Hmm maybe Ill try photo'ing something with my phone....

The first part is good. condition #3 is met by the 7 image. Both the backstroke and downstroke must intersect at the point of the 7 which must be precisely located so the downstroke plane is parallel to the plane line otherwise compensations are required.

The second part- I believe that HK "prefers" the shoulder move on the same plane as the hands- 7-13 paragraph #2. This is logical as all energy to the club flows through the hands. therefore any "off plane" to the hands will be dangerous.

Same disclaimers

HB

I think we're saying the same thing here maybe cause that only happens when their both on the same plane, ie when the Right Shoulder is on the Inclined Plane in Startdown (TSP by definition). Startdown the period of Shoulder of Acceleration by definition. Hands are always on the Inclined Plane , if the Right Shoulders gets on it too at Top...you got a TSP angle of which there is a range I suppose.

I tried doing a few drawings, when you get into all the parameters , TSP, Flat vs Rotated , zero or single or double shift.......it gets messy. Need to do them to proper scale to make the implications to shaft angle at impact, waste bend clear and relevant. Hard to do on the beach.... But they would describe TGM's Standard Shoulder Turn , S and T Rotated/? Double Shift and I was looking at Matt Kuchar there in pencil form too on one of them.

Im thinking this'd be a good thing to doodle out .....the photos in the book are great but some simple stick men that would also combine the various related components (TSP, Standard Shoulder Turn, Zero Shift or minimal a shift) would make for a nice presentation of one of Homers most brilliant ideas....... Maybe we could Yoda to offer an opinion to make sure we're book compliant. One thing though .....I dont think you can do it with a hanky under your arms. You need independent arm motion (independent of the PIvot).

In any event .....Why is the Alignment Golf Shoulder Turn "Flat" on the backswing (only, not on the way down)? To try to get the Right Shoulder over to the Elbow Plane or as close to it as is possible. So as not to necessitate a shift of any large degree during the Downswing. Final final answer. And of note. Just because the Right Shoulder turns Flat does not mean the Hands are going back flat given Independent Arm Motion. A free connection where the Arms meet the Shoulders (Pivot). Right Shoulder turns IN, Hands go UP , but they meet up on a TSP and share a ride down the Inclined Plane..

I keep saying that bit.....its the brilliant result of these component combinations, this pattern. Genius. That or Im totally crazy.....or both I suppose, if you want to catalogue all the possibilities , Homer would.

Homer listed TSP for the Plane Angle, Zero Shift and Standard Shoulder turn for both Basic Patterns of 12-1 and 2. You can argue whether Zero is really possible but assuming minimal shift as a goal anyways ........He was clear in his preferences and from my experience Id have to say he's correct. Very correct. But not commonly understood maybe? Its too bad, it'd be revolutionary and its already 40 years old. That said you do have options.....not saying Double Shift is not workable.