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スパインのすべて|エグゼクティブサマリー|The Tutelman Site

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All About Spines by Dave Tutleman, 30 January 2008

拙訳

遡ること2006年2月,John Kaufman(振動数メーター会社である Club Scout のヘッド)が,SpineTalkerのフォーラムでこう質問した。 *1

やあ諸君, *2

動きがとても遅いので,シンプルな質問をするよ。シャフトのスパインのアライメントすることで,何を達成しようとしてる? あるいは,何を避けようとしている,と訊くべきかな? 過去何年か聞いた話を総合すると,たぶんこの疑問は見かけほどは明らかじゃないんじゃないかな。 *3

シャフトスパインが興味深いのは,「スパインをアライメントすること」がゴルフクラブの打感かパフォーマンスかに影響を与えることがあるという証拠があることだ。スパインをアライメントするとは,ホーゼルの中でシャフトを回して,クラブを組み立てるときに,そうすることでそのシャフトのスパインがある特定の方向を指すようにすることだ。例えば,クラブのヒール=トウ・プレーンにスパインを合わせることもある。もちろんこれは,シャフトをクラブヘッドに挿すときに行なわれなければならない。 *4

Johnがその問いを投げかけた翌日,回答がいくつかあった。「ゴルフ規則の中でシャウトのパフォーマンスを最大化しようとしている」などという文面とともに。それでJohnはもう少し掘り下げた。 *5

私の簡単は質問は,短すぎたようだ。君たちは,シャフトをアライメントすることで達成したいと望む結果のすべてを述べてくれた。しかし,アライメントするとき,どうしてこれらのことが起こるのだろうか? *6

その質問は非常に自明ではなかったという点で正しい。1ヶ月ぐらいして,私は最初に考えついたことを,概要をまとめてフォーラムに投稿した。しかし,記事にまとめるには,約2年を要した。それがこれである。 *7

あらかじめお断りするが,これはスパインについての普通のクラブフィッターの見方ではない。これは,エンジニアの観点から見たスパインであり,直感とごまかしは表に出てこない。「共通理解」から私の観点がどのように違っているかを指摘したいが,それをすべての箇所で行なえたわけではない。 *8

スパインについての間違った考え方と誤解とが,多くのゴルファーそしてカスタムクラブメーカーとに広まっているので,私はまずはそこから始めて,Johnの質問に答えていきたい。 *9

エグゼクティブサマリー *10

最初に,スパインの計測方法とアライメント方法に関するアドバイスだけを求めているから,以下が結果のサマリーだ。なぜこの結果になるかを知りたければ,このサマリーだけでなく,記事全体を深く読んでいく必要がある。 *11

  1. スパインを探すために,ベアリングをもとにしたスパインファインダーを使わないこと。それは間違った答えを出すから。代わりにFLO(Flat Line Oscillation)を使うこと。 *12

  2. FLOプレーンのうち振動数が高いのが,スパインの組だ(180度離れている)。FLOプレーンのうち振動数が低いのが,NBPの組だ(こちらも180度離れている)。スパインのプレーンとNBPのプレーンとは,90度の角をなしている。 *13

  3. その派生として:もし計測して,スパインがNBPから180度離れている(本当は90度なのだが)という結果が出たら,その計測プロセスかその計測器を捨て去ること。間違った答えを出しているから。 *14

  4. ふたつのFLOプレーンのあいだの振動数の差を計測する。それが3cpmより小さければ,スパインアライメントをしたところで,打感にもフィーリングにも何ら影響を与えない(アライメントすることで心の平静は得られるだろうが)。 *15

  5. スパインをアライメントする方向で,これがベストな方向だというのは証明できない。いろいろな理論があり,実験結果も決定的な結論を出していない。しかし,多くの実験と実践によれば,スパインをヒール=トウ・プレーンに合わせ,NBPをターゲットプレーンに合わせるのが良さそうだ。もっともありえそうな理論も,その向きを支持している。 *16

  6. NBPをターゲットに向けるか,ターゲットから離すべきか,と尋ねたければ,あなたは注意力を欠いていた。さかのぼって,ポイントaからeまでを再読しよう。それらポイントに同意すれば,この質問は意味をなさない。 *17

さて,この記事のポイントを列挙する。ある種の目次だ。それぞれのポイントが詳しく記されている記事へのリンクを張った。 *18

基本的な定義と物理学 *19
スパインの検知と測定 *30

分析結果,そして経験則が,この立場を支えている。 *34

スパインアライメント *35

最後に,Johnの質問に至る。つまり,シャフトを挿すときにアライメントをすることで,私たちはどのようなパフォーマンスの向上を期待しているのか? *36

未決事項 *47

他のカテゴリーにはうまく当てはまらなかった,いくつかの事項。 *48

結論… *53

クラブメーカーの大部分がゴルファーを信じさせようとするほどには,私たちはスパインアライメントについて多くのことを知らない。そして,私たちが「知っている」と思っていることのほとんども,真実ではないかもしれない。実際,いくつかのことは明らかに間違っている。 *54

全記事

*1:Back in February 2006, John Kaufman (the head guy at Club Scout, the frequency meter company) asked on the SpineTalker's forum,

*2:Hi Folks,

*3:Since things are so slow I have a simple question to ask. What are you trying to accomplish by spine aligning a shaft? Or maybe I should say trying to prevent? From all the talk I've heard over the years maybe this question isn't as trivial as it sounds.

*4:Shaft spines are interesting because there is evidence that "aligning the spine" can affect the feel and/or performance of the golf club. Aligning the spine means rotating the shaft in the hosel, while building the club, so that the spine of the shaft points in some specific direction. For instance, the spine can be placed in the heel-toe plane of the club. Obviously, this has to be done at the time the shaft is installed in the clubhead.

*5:The next day after John posted his query, there were a few responses along the lines of "we are trying to optimise the performance of a golf shaft within the rules of golf". That caused John to elaborate a bit:

*6:I guess my simple question was too brief. You have stated all the results we hope to achieve by aligning shafts. But what causes these things to happen when you align a shaft?

*7:John is right that the question is very non-trivial. I posted my initial thoughts in the form of an outline within about a month, but it took almost two years before I was ready to write it up as an article. Here it is.

*8:Be forewarned, this is not the usual clubfitter's view of spines. It is spines as viewed by an engineer, so intuition and hand-waving are going to take a back seat. And, unfortunately, too much of what is "generally known" about spines falls under the heading of intuition and hand-waving. I'll try to point out where my views deviate from the "common wisdom", but I may not have done it everywhere.

*9:Because of all the fallacies and misinformation about spines, among both the public and custom clubmakers, I'm going to start at the beginning and work my way from there to John's question.

*10:Executive Summary

*11:First, if all you want is advice on how to measure and align spines, here is a summary of the results. If you want to know why these are the results, you will have to read further than this summary.

*12:Don't use bearing-based spine finders to locate the spine; they give wrong answers. Use FLO (Flat Line Oscillation) instead.

*13:The high-frequency FLO plane is the pair of spines (separated by 180); the low-frequency FLO plane is the pair of NBPs (again, separated by 180). The spine plane and the NBP plane are separated by 90*.

*14:Corollary: if your instrument tells you that the spine is 180 from the NBP (instead of the proper 90), throw away the procedure or the instrument that tells you that. It is giving you wrong answers.

*15:Measure the frequency difference between the FLO planes. If it's less than 3cpm, spine alignment is not going to do anything for performance or feel (though it may give you some peace of mind).

*16:There is no provable best direction for aligning the spine. Theories differ, and the experimental evidence is not conclusive. But most experiments and practice say to place the spine in the heel-toe plane and the NBP in the target plane. The most likely theories also support this alignment.

*17:If you want to ask whether to place the NBP toward the target or away from it, you weren't paying attention. Go back and read the points a-e again. The question makes no sense if you accept those points.

*18:Now for a list of the points in the article, a sort of table of contents. Each consists of a link to the place in the article where the point is elaborated.

*19:Basic definitions and physics

*20:Shafts are not perfectly symmetrical. They have directions where the shaft is stiffer and directions where the shaft is "weaker" (as in "less stiff").

*21:"Spine" is the term for the stiff direction.

*22:"Natural Bending Position" (NBP) is the term for the weak direction.

*23:Every shaft where the spine is big enough to be discerned has:

*24:Two spine directions, 180º apart (that is, opposite one another).

*25:Two NBP directions, 180º apart (that is, opposite one another).

*26:The spine directions are 90º from the NBP directions.

*27:When a shaft bends during the golfer's downswing:

*28:Not all the bend is in the same plane. There are large early bends near the heel/toe plane, and smaller bends in odd directions late in the downswing.

*29:The bend at and just before impact is not neat enough -- nor consistent enough from golfer to golfer -- to be a factor in any simple rule for spine alignment.

*30:Finding and measuring spine

*31:Bearing-based spine finders, sometimes called feel finders, don't work reliably. If the shaft has any residual bend (even too small a bend to notice without very careful measurement), then that bend has a significant impact on the direction the instrument finds.

*32:FLO is the "gold standard" for finding the spine. FLO refers to finding the shaft's planes of "Flat Line Oscillation". These two planes are the spine plane and the NBP plane.

*33:Differential deflection works reliably, but is more tedious than FLO.

*34:Both analysis and experimental evidence are presented to support this position.

*35:Spine alignment

*36:Finally we get to John's question: what are we doing to or for performance when we align the shaft in the club?

*37:"Spine alignment" means having the spine and/or NBP face in a specific direction when the shaft is installed in the clubhead.

*38:There is some experimental evidence that it works (that is, it has an effect on performance and/or feel), though hardly universal agreement on what alignment technique works.

*39:Residual bend without spine has no effect on performance. There is no reason to align shafts based on residual bend.

*40:There are plenty of theories why spine alignment should work. We examine them. None fits the data perfectly, but some fit better than others.

*41:You should align so that the direction the shaft 'wants' to bend is in the target plane at impact. This sounds nice and intuitive, but is never offered with a sound physical rationale -- and I could not find any. Not viable.

*42:Placing the NBP in the target plane allows the hands to square the clubface at impact. This is plausible, based on the assumption that the shaft bend is in the target plane in the vicinity of impact. Unfortunately for the theory, the shaft bend is not in the target plane during the tens of milliseconds before impact. Not viable.

*43:When the shaft bends during the downswing, any bend not in the spine plane or NBP plane produces forces that tend to move the clubhead out of the swing plane. This is definitely a true statement. The question here -- so far unanswered -- is whether those forces are large enough to produce the observed results of misalignment. Possibly viable.

*44:Since the shaft bend at impact is in the vicinity of the clubhead's center of gravity (CG), align the NBP with the CG -- using the same rationale as #2 above. This theory suffers from an assumption contrary to fact. The shaft bend at impact is not in the direction of the CG. Not viable.

*45:The advantage is in feel at and after impact, where the clubhead "rebound" from the ball is in the target plane. This is consistent with experimental results based on feel. It is not as clear in explaining experimental results reporting performance differences. Possibly viable.

*46:Any consistent alignment strategy results in a consistent set of clubs, and that is the best we can expect to do. This does not explain why experiments tend to show that certain alignment positions seem to be better than others. Not viable.

*47:Loose ends

*48:Some things that don't fit neatly into the other categories:

*49:My own strategy for dealing with spines is detailed here.

*50:What causes spines? What causes the direction of the spine to change when the shaft is trimmed?

*51:Spine can be considered negligible if the effect of misaligning it produces no measurable effect. This level is calculated to be somewhere in the range of 4cpm.

*52:A rant about the rules.

*53:Bottom line...

*54:We don't know nearly as much about spine alignment as most clubmakers would have you believe. And much of what we "know" may not be true. In fact, some of it is demonstrably false.