Golf Club and Clubmaking/Clubfitting terms (part 3)

15. Bend profile. Every shaft has a different bend profile. Shafts do flex, this we know. But shafts are also designed for certain performance aspects. No two are the same even from the same manufacture. We have designated certain shafts into certain categories. For example; some shaft have stiffer but sections while other shafts has more flexible butt sections. The same can be said about shaft tip stiffness’s, some are weaker then others. The overall bend profile is what makes a certain shaft play the way it does. Just an no two golf shaft share the same bend profile, neither do golf swings, no two are alike. That being said, it is very difficult to determine which shaft is correct for which type of swing. Ah, we can “type” swings by generalizations as a beginning. For example, a golfer with a higher swing speed and a quicker tempo would be better suited to use a shaft with a stiffer bend profile verses a smooth swinger with a slower swing speed. The slower swinger can use a more flexible shaft with a softer bend profile. This is a discussion all on it’s own and we will get into this topic deeply in coming weeks. For now, a general description is good enough to suffice most.

16. CPM. Ah the most abused acronym is the club building handbook. CPM stands for “cycles per minute”. Cycles per minute are arbitrary measurements of the movement of a shaft in a period of time. Typically the butt end of the shaft is clamped in a five inch long vise that applies equal pressure over the five inches of the shaft. A weight of known value is attached to the tip of the shaft to provide “movement” or flex. The shaft is oscillated in either a horizontal or vertical movement so the tip weight moves back and forth in a single plane. The amount of “movements” up and down are equal to the “cycles” in a one minute time period, thus CPM. The higher the CPM reading, the “stiffer” the shaft. Stiffer shafts have less flex so the period of time from going “down” to coming up is shorter (less distance traveled) so the shaft “cycles” much more often. CPM is only a starting point in determining overall shaft flex, there’s profiling and other means to determine overall shaft flex, again this is an advanced topic that we will discuss in at a later time.

17. BBGM. This is an acronym that stands for “bottom bore ground measurement”. Every golf club has the shaft attached via some mechanism. Most club have a housel where the shaft is inserted and then glued together. There are three different housel types or “bores”. A standard bore in ~ 1.5” in depth with most of the bore exposed on the top of the club head. A blind bore is built down into the club head and bottoms out somewhere between the sole of the club and the top of the head. A through bore is one where the shaft goes completely though the head and is ground even with the sole of the club. BBGM is the measurement of the bottom of the bore to the sole of the club. For example; a Ping G2 club head has a 1.5” bore depth. From the bottom of the shaft bore to the sole of the club is equal to 1.5’ so the BBGM would be 1.5”. A though bore such as the Titleist 905 head has no BBGM, the TM R5TP has a 2” BBGM. The BBGM is significant because this lets us know how much weight is hanging off the end of the shaft. A shaft installed in a club head with no BBGM will play significantly stiffer then when installed in a head that has a 2”BBGM, it’s the additional weight of the head hanging on the end of the shaft that makes the difference in flex.

18. Spine. This is a term to describe the overall roundness of a golf shaft. No shaft is perfectly round due to variances in manufacturing. Most shafts have a seam that is “stiffer” then the other parts of the shaft wall. Some shaft are “oval” and will have two stronger “spines”, one will be weaker then the other so one is called SP1 and the other SP2. There are a lot of opinions about shaft spines and how the shaft should be installed in the head. I for one could give a rats arse about spines but then again I use FLO for alignment and FLO wasn’t available back in the early days of club making.

19. FLO. This is a term to describe the movement of a shaft in a single plane. Referencing the above “spines”, no shaft is completely round. However, every shaft has a point in the circumference where the alignment of the materials is stable and the shaft bend is predictable. We call this “flat line oscillation”, this is when the shaft flexes easily in a single plane, back and forth with little movement side to side. This is the most predictable and stable part of the shaft. The shaft moves up and down in a near straight line with little resistance. If resistance is present, the shaft will move in circles and not in a single plane. Since we all try to deliver the club head on a single plane to impact, then it’s best to align the FLO plane of the shaft to compliment the single plane of impact. The FLO plane is the true flex of the shaft.

20. Kick point. I absolutely detest this term or description when describing golf shafts. First off no shaft is “bent” at actual impact; nope the shaft is straight as an arrow and has no flex or bend. You see golf shafts are just like any other material in that shafts like to be straight and will resist being out of the “vibration” plane. All material have a vibration plane, you name the material and I can guarantee that it indeed has a vibration plane. Vibration planes are basically the binding of electrons that form the overall martial from various elements. Steel is hard, yes but steel has a vibration plane as well. Some vibration planes are “tighter” then others; materials with tight vibration planes are hard material with little flex or movement. On the opposite side of the spectrum, materials with loose vibration plane tend to be soft in nature and move freely. One common aspect of both hard and soft materials is both want to be in the single “zero“ vibration plane, that’s means no movement. Changing or moving the vibration plane causes resistance, resistance is where the energy come from in terms of shaft loading. When we swing the driver back, we have little if any resistance. As we initiate the down swing, the shaft resists the change in vibration planes and thus the shaft flexes. We all feel this resistance so we swing a little faster, harder etc. This is “shaft” loading, the shaft resists our movement down and this is where we accelerate our motion, because of the shaft resistance. As we approach impact, we have less resistance (gravity is equal) and the shaft by nature returns to the zero vibration plane or “straight” up and down. This is what some people refer to as “shaft kick”, the shaft returns to a zero vibration plane. As long as your hands / arms / body continue in motion, the shaft will no bend forward, it’s impossible. So shaft flex is important and can be matched to tempo, release etc. In order to fit a golfer for the perfect shaft, one has to look at the tempo, release point and overall resistance to the swing i.e shaft loading.

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True Length Technology Fitter - www.truelengthtechnology.com
It's live! - www.ShipShapeClubs.com
PCS Class 'A' Clubfitter

A new highlight: Golfing the home course on Christmas Day.

I say it too often: If it's golf club shaped, you can play with it.

For the record, I'm a club doctor, not a swing doctor.

This seems to be inconsistent with the shaftlab discussion on DaveT's site.

http://www.tutelman.com/golf/shafts/ShaftLab.php?ref=