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Lessons from Progressive Launch Iron Sets

I get a lot of comments from readers of my golf shaft site, GolfShaftReviews, that they love the information but do not understand some of it. Much of this article will be a discussion of golf shaft EI profiles. If you are new to this term, my friend Dave Tutelman published an article explaining the basics many years ago.  I wrote a more detailed discussion in these articles, Golf Shaft EI Profiling and Beyond Frequeny Matching  on GolfShaftReviews.  Other articles on this site further explain the background information you may need to understand this discussion.

I have been devoting a lot of time lately to completing the Fit2Score shaft profiling software that is now available through subscription. Many years ago I developed a spreadsheet for owners of my EI instrument that quickly profiles a set of shafts destined for use in a set. I call the process Iron Set Certification. The certification spreadsheet serves the club builder as a place to store not only the shaft data for a set, but most other aspects of the set; head brand, weights, balance, loft, lie, length, grip, etc. for future reference for that client. Using this software I have profiled a vast number of iron shaft sets. It became apparent that not all sets of shafts had the same bend profiles through out the set. In many sets there was some degree of flighting between the shortest shaft and the longest shaft in the set. I first heard the term flighting in reference to Project X shafts when they were made in Brunswick Connecticut by the Royal Precision. Flighted sets are designed to launch the long irons higher and the short irons lower. The objective is uniform ball flight height through out the set. The benefit is tighter distance gap control between clubs.

Be patient with me while I discuss a little more history. When I began as a hobby club builder 17 years ago I was introduced to shaft profiling using a frequency instrument. This is not simply measuring the butt frequency of a shaft. The shaft is measured at 5″ increments from tip to butt. The software that supported that system compared irons by looking at 6 irons only. When I developed my EI software I followed that model, writing my system to compare the bend profiles of 6 iron shafts. As I did numerous iron set certifications it was apparent how shortsighted only comparing 6 iron shafts was. An important aspect of iron shafts is the difference in bend profiles between the long and short iron shafts in the set. The complexity of converting 16 years of work to set profiles from 6 iron only profiles kept me from addressing this issue. About a year ago with the release of the True Temper Dynamic Gold Pro I decided it was critical to the understanding of irons shafts to incorporate set profiles. The view of irons as sets, that came from set certification profiles, needed to be brought into the Fit2Score shaft software system. It took a year to complete and debug the system software upgrade. I am still in the process of loading the data for the 300 iron shafts I have profiled in the past.

I have been looking at golf shaft EI profiles for 15 years. On this venture I continue to discover and understand nuances of shaft design and performance. This article is an attempt to explain an understanding of iron shaft sets that has developed over the last 5 years. If you get it on the first read, congratulations.

The amount of flighting in iron shaft sets varies from manufacturer to manufacturer, and from model to model. A good understanding of EI bend profiles can be seen in shafts sets that were intentionally designed for progressive launch. I wrote a detailed review of such a shaft, the Dynamic Gold Pro, last year. Read it as background information about flighted or progressive launch iron sets.

DGP-RSXLook at the difference in the upper chart between the bend profiles of the wedge, 6 iron and 2 iron shafts in these sets. The vertical axis is the stiffness of a 10″ section of the shaft, centered at the position noted in the horizontal axis. The tip is to the left, the butt to the right. You can see that the butt of the shaft is stiffer than the tip. The tip is not always the softest section of the shaft. Very often the softest section is 10 to 12 inches up from the tip. If your measuring technology, for example frequency, does not allow accurate readings in this range, you are flying blind.

As you look at the R, S and X flex versions in the upper chart, you see that the entire curve moves upward as the shaft gets stiffer. And, in this model golf shaft, the shape of the profiles change as well. This is not true of all shafts. It is another reason that knowing both wedge and long iron profiles are important to the tour level fitter.

You can see how much flatter the wedge shaft profiles are than the 2 iron profiles. The steeper the change in stiffness from tip to butt, the higher the shaft will launch. The point where the bend profiles change the most is an indicator of shaft contribution to launch. The closer the maximum bend point is to the butt, the higher the shaft will launch.

The lower chart, shows the change in stiffness point to point on the shaft. It amplifies the understanding of the bend point of the shaft. You can see how the change in stiffness, especially in the R flex model, is steeper and moves significantly toward the butt in the 2 iron shafts. This method, looking at change of stiffness, is essential to understand shafts through their EI profiles.

Understanding the EI profiles is tricky. As you look at the actual profiles your eyes are drawn to the lowest point on the shaft, where it changes from losing stiffness to increasing in stiffness. But in the lower signature chart, the change of stiffness is not greatest at the lowest point of the EI curve. It is higher in the shaft, closer to the butt, where the shaft is rapidly losing stiffness. Doing a compression test on the R Flex 2 iron shaft, the point where the shaft bends is 17″ from the tip. This is exactly the spot that is the lowest in the profile signature chart of this shaft.

And that is a simple understanding of reading shaft launch propensity from 3 point EI data. This is not clearly shown in frequency or deflection profiling systems. But it is hard to miss in 3 point EI profiles. And that is why 3 point EI profiles are the language of shaft designers.

DGvsDGPLets take a quick look at the Dynamic Gold X100 and the Dynamic Gold Pro X100 wedge and 2 iron shafts. The Dynamic Gold X100 is a very flat profile as iron shafts go. There is little launch assistance and the wedge and 2 iron have the same profile. The wedge is stiffer, as indicated by being higher on the chart, but there is very little difference between it and the 2 iron shaft. Now look at the Dynamic Gold Pro X100. First you will notice a distinct zone in the 12″ to 22″ area where their is a noticable loss of stiffness. And, that loss of stiffness is more pronounced in the 2 iron than in the wedge.  Then, with the profiles superimposed on each other, you can see the wedges are quite similar. The 2 iron shafts are noticeably different. This illustrates why a fitter needs to know set profiles, not just 6 irons.


A golf club fitter needs to know the properties of the shafts he is fitting you with. I first learned about shaft profiling from Tom Wishon. He assembled a database of linear shaft bend profiles using a strain gauge frequency instrument. It got my interest and I put a great deal of time into frequency profiling shafts on my own and developed a rudimentary database of my own.

During a visit to a shaft company R&D site I was introduced to the concept of EI profiling. That began my exploration of other methods of describing the properties of a golf shaft. I learned the term EI from engineers in the business of designing shafts. The instrument used was in the $10K+ range, not affordable to most. Not even all shaft companies had these instruments.

It took about 2 years to come up with an workable, affordable EI measuring design. After many years of use, I decided it was time to redesign and improve the original. I knew all the sources of error in the original design and fixed them. The machining was beyond the capacity of my mill and I had to outsource the cutting of the parts. The precision of the parts made by a machine shop further improved the instrument and made designs I could only imagine possible.

The new design far exceeded expectations. Most of the original instruments have been upgraded. A number of my instruments are now owned by shaft companies. The latest to acquire one has reported it is the fastest, easiest to use and most accurate instrument in the business. The first production run of the new instruments is nearly sold out and a second production run is commencing.

Recent promotion of hoop strength by a shaft company lead me to explore how hoop strength is measured. One method is compression testing. A tube is placed on a block and a weight is placed on it. The amount it bends under this load is a measure of hoop strength. After a few tests I designed a support and added hoop strength measurement to my instrument and database.

With a driver shaft database of 1200 shaft profiles that include stiffness, torque and hoop profiles, I and my affiliated fitters know the shaft you are being fit with. That knowledge makes us exceptional fitters. Six of the fitters using this system are on the recent Golf Digest Top 100 ClubFitters list.  To learn more about the instrument and software look at the bottom of the Products page for links.


Custom Built Clubs – Golf Shaft Set Certification

I have been using the prototype of our new version shaft EI instrument for several months. The parts are now being machined and distribution of the upgrade and the new instrument will begin in July of 2014. Much of my software is being revised.

When I custom build iron sets I document the measurements taken. Often the measurements include checking every shaft in the set. This is offered as an additional service. On occasion a shaft in a set is an outlier. It does not match the rest of the shafts in the set, or it has a weak or hard spot along its length. That shaft gets returned to the manufacturer and replaced. Without having each shaft checked, you will never know if your set is consistent. The following report is provided to document the certification and building specifications on custom built sets.


Understanding the differences in golf shafts has never been easy. There are a lot of terms used to define a shaft, too many to review in this article. Without any industry standard, they have little value to anyone trying to understand the differences between two shafts. Over the time I have been involved in club fitting, I have tried several systems. Each had limitations and finally, I gave up and invented my own. Yes, I added one more system to the plethora of systems already in use.

That system is based on text book mechanical engineering beam theory. Bending is he product of the elastic modulus E and the area moment of inertia I of the beam cross section at a point on the beam. The formula looks like this:

w is the bending of the beam, x is the location and k is the curvature. This is the fundamental science used by all golf shaft designers of significance. It makes simple sense to use the same system to understand their designs.

What this formula means is that if you know the EI along the shaft it can be transformed into the bend profile of the shaft as shown in this illustration.

I picked these two shafts to illustrate the value of knowing the EI profile of golf shafts. These two shafts are both rated by their respective manufacturers as S flex. The EI profile shows the butt and tip stiffness to be about the same. And yet, they show very different bend patterns when loaded as shown on the right.

The loading illustration is what you would see if you used a deflection board. I borrowed this image of a deflection board from GolfWorks. This is a classic tool used by clubmakers to understand shaft bending properties and to rate stiffness.  Frequency instruments have replaced this instrument in most club makers shops. Frequency gauges give the club maker a number from which many systems translate frequency of oscillation to stiffness. What is not seen on frequency instruments is the bend profile seen on a deflection board. The shortcoming of deflection boards is that they do not quantify the bend profile, leaving the club maker to compare bend properties with tracings.

Using EI values along the shaft, the deflection profile can be calculated and quantified as shown. And this lets a shaft engineer translate material properties, shaft wall thickness, shaft wall diameter and shaft taper into computer simulated bend properties of a golf shaft.

The club fitter, equipped with EI measurements, understands the bend properties of the shafts he fit with.

And that understanding is why I felt it was necessary to invent my own instrument and system for measuring golf shafts. The amount of load applied during a golf swing is transformed into shaft deflection. The amount of deflection is what you feel as stiffness when you swing. Feel feedback helps you time your swing. Too much deflection creates dispersion, too little, bad timing. The EI bend profile determines not only the amount of deflection but also the shape of the deflection. And that shape influences how your swing presents the club head to the ball at impact. EI profiles guide me in fitting my clients into the best shaft for their golf swing.

This is a study of the radial properties of 6 shafts.  It is a supplement to the golf shaft alignment video. I discussed bow vs spine in that video, and mentioned that the two did not necessarily align with each other. But the example used in the video very closely aligned with one of the FLO’s. In this larger study of 6 shafts, there are examples showing more clearly the point that was made in the video.

The charts below show the effectiveness of the Three Point bearing tool, often referred to as a spine tool and a tip weight laser tool in locating the radial stiffness high and low points of a driver shaft.  The tip laser device, often refered to as Flat Line Oscillation FLO or Vertical Oscillation Plane VOP was an effective tool for finding the stiff and weak planes of the shaft.  This can be accomplished by the club maker by FLOing the shaft in a CPM device and noting the CPM of the shaft at each of the two FLO planes.  The stiff and weak planes are easily identified.

The bearing based Spine tool is not a reliable device for identifing the stiff and weak planes of a shaft.

This study was inspried by the writing of my friend, Dave Tutelman.  This link is his article on the subject,

Four properties were measured as follows:


The stiffnes of the shaft as measured every 10 degrees.  The shaft was clamped at the butt end, the tip was deflected 1″, the load cell was set to zero.  The shaft was then deflected 5″.  This method measures the stiffness of the material without any affect from any bowing or curvature in the shaft.  The readings are shown as the blue line.  The readings were smoothed to eliminate measurement ‘noise’.

Vertical Oscilation

A weighted laser tip was attached to the shaft.  The shaft was deflected 3″ and released.  The laser trace was recorded in a 5 second timed exposure.  The shaft was rotated until a stable plane of oscillation was found.  The photo of the trace is shown to the right of the shaft.  The shaft was then turned 90 degrees and the second stable plane was located.  The solid red line shows the stable plane of the shaft closest to the stiff side of the shaft.  The dashed red line, the stable plane that was on the softer side of the shaft.


Using a three point bending tool the bow of the shaft was located.  This tool is a pair of bearings in a tube.  The shaft is inserted into the ID of the bearings and a third bearing is used to deflect the shaft.  The shaft turns to the bowed side to minimize the stress of the loading force.  The Bow is shown as a Yellow line.

Tip Deflection

The shaft was inserted into a machining chuck which can be rotated.  Two pieces of card stock were bent 90 degrees and set against each side of the tip.  The shaft was rotated.  The cardstock was pushed away from the shaft as the tip moved during the rotation.  The points of maximum deflection to the right and left were noted and indicated by the black line.



We recently updated this blog and changed our video hosting platform. I had to go through all the posts and relink the videos. This post falls into a category I must call legacy material. It was early in my discovery of EI profiling and shows version 6 of my instrument. Its crude compared to the current instrument, and so is the production. But, it has been watched thousands of times. It is on the list of productions that need a remake.

Golf Shaft Flexural Rigidity – EI Profiling

Young’s modulus is a measure of the stiffness of an elastic material.  It is often used to determine the strength of a beam.  Shaft stiffness varies along the length of the shaft.  Using Young’s modulus, the ratio of stress to strain, a shaft can be measured at different points along its length.  This has come to be known as shaft profiling.  When the values are expressed per Young’s modulus, this is called EI Profiling.  Other databases, using different methods to measure stiffness, are also used for the same purpose.  A fitter uses knowledge of the flexural profile of shafts to quickly find a shaft that fits a golfers swing.

Golf Shaft Stiffness Measurement

The flex terms one commonly sees, R, S, X have little meaning to a fitter that knows the EI profiles of the shafts he uses.  As one comes to understand the many, many shaft stiffness profiles available today, flex letters become little more than a shaft manufacturers method of swing speed rating their shafts.  There is no uniform standard for defining shaft stiffness.  And as you develop a knowledge of EI profiles, you understand the futility of thinking that a standard could be defined.  Each design will load and unload differently in the hands of different golfers.  What works for one style of swing at a particular speed will behave differently with a different swing style at the same speed.

Golf Shaft EI Measurement Instruments

When I learned about EI profiling, I discovered there was no uniform system for measuring beam stiffness of golf shafts.  Laboratory instruments used by some shaft companies, cost in excess of $10,000.  A friend and I undertook the design and creation of a EI measuring instrument.  Our objective was to use gravity to apply the load that is applied by hydraulics in the expensive laboratory equipment.  When an early version of the instrument was shown at a club making convention, many asked that we make a machine for them when making our own.  Guiding weight without introducing friction lead us to invest in a milling machine.  Producing 15 machines for friends took all of our spare time for 6 months.  Today, 2 years later, databases with hundreds of shafts, are shared among the owners of the EI measuring instrument.