Golf Shaft EI Instrument

By Russ Ryden, A Golf Digest America’s 100 Best Clubfitter
Fit2Score, Dallas Fort Worth, Texas

Several years ago I learned the term EI from engineers in the business of designing shafts. The instrument most used was in the $10K+ range, making if not affordable to most. Not even all shaft companies have these instruments. It took about 2 years to come up with the original affordable EI measuring instrument design. This shaft review site shows measurements taken with the Fit2Score instrument.

After many years of use, I decided to redesign and improve the instrument. The improved Fit2Score EI shaft measuring instrument is now available. This animation show it cycling on a shaft.

The gauge is re-positioned to improve accuracy and repeat-ability on measurements. Positioning pins are incorporated into a manufactured weight. Most of the original instruments have been upgrade with these assemblies. The newly designed self centering shaft support maintains the radius of the earlier design while eliminating guides to center the shaft. The shaft naturally ‘falls’ to the bottom of the curve making readings faster and repeatable.

A hoop stiffness measuring fixture has been designed. It centers the shaft under the press and uses the 11kg weight and .0001 gauge to measure hoop stiffness. The updated database structure includes fields for hoop stiffness readings along the length of the shaft. This pulls aside another veil of understanding the golf shaft, giving the club maker a method to evaluate marketing claims.

The instrument is now available for $3000. Excel based spreadsheets are included for gathering and analyzing profiles of shafts. Owners have the option of subscribing the the historical knowledge base that is at the core of the reviews on this site. Contact russ@fit2score.com if you are interested in this essential club making instrument.

Golf Shaft Hoop Strength

By Russ Ryden, A Golf Digest America’s 100 Best Clubfitter
Fit2Score, Dallas Fort Worth, Texas

Hoop strength is discussed endlessly in the marketing of golf shafts but unlike other specifications, we are given no information about actual strength of one shaft vs another. After trying a few methods to measure hoop strength I arrived at the method shown to the right. It is a text book method, place a tube on a firm surface, drop a weight on it and see how much is deforms. I built a small block, slightly higher than the guides used for EI measuring and now have a tool for quantifying hoop strength. If this is a new term for you, follow this link to the AeroTech web site for a discussion. For those readers familiar with the term, you should note that the shaft in this image has some of the highest hoop strength I have yet to measure. It is a pull out that I played many, many years ago before I developed the current passion for understanding the golf shaft. A material called triax was wrapped into the shaft to add hoop strength and eliminate ovaling during the golf swing.

My first attempts to measure hoop strength were to look for ovaling. I clamped a shaft on a deflection device, measured the diameter at different points, bent it 5″ and measured again at those points. The differences were so small I decided there was more noise in the numbers I was reading than the variance I was trying to measure. I could not find .001 inch of difference. That might just make the rest of this article a waste of time, but if you are interested in the concept read on. With the device pictured above, the shaft is compressed with 11 kg and a change in diameter is apparent. The scale on the graphics is .002 inch increments.

Carbon Fiber Iron Shafts

The focus of this article is iron shafts. I have not yet measured the shafts in my driver fitting system. Lets start by looking at my hoop strength measurements of some popular graphite six iron shafts that I fit with. Graphite wall thickness in heavy iron shafts creates high hoop strength. AeroTech maintains high hoop strength even as the shafts become lighter as a result of the filament winding process they uniquely use and the stainless steel wire wrapped around the shafts.

What you see looking at these charts is that heavy graphite shafts universally have high hoop strength. And even light weight graphite, the 70 gram AeroTech and the 60 gram Fujikura MCI, which also employs a metallic fiber in the shaft walls have high hoop strength.

As you look at these charts, take note that a low number, meaning very small deflection under load, indicates high hoop strength.

Steel Iron Shafts

Now lets compare the hoop strength of some popular steel iron shafts. We immediately see less hoop strength in the butt sections of steel shafts. This is not limited to a particular brand, it is universally true.

What I found really interesting was that the hoop strength profiles were the same shape as the EI profiles. The stiffness of a steel shaft is determined by the wall thickness and the diameter of the shaft.

The material, a steel alloy, is consistent through out the shaft. In contrast, carbon fiber composite shafts material properties can change through out the shaft.

But wait a minute. I looked at both the Modus3 Tour 120 and the Modus3 Tour 130. Both have very different EI profiles. Yet, the hoop strength profiles are similar. Nippon steel has some interesting technology in their production lines.

Light Weight Steel

One final image, a comparison of Ultra Light Steel to high quality light weight carbon fiber iron shafts. Do not come away with the impression that all light weight graphite shafts are going to have hoop strength like the high end shafts you see here. They do not.

What does it all mean to your game. I cannot say with certainty at this point how hoop strength manifests itself in shaft stability and dispersion control. Or if it can create kick velocity. Nor can I give you direction on what amount of hoop strength is appropriate for your loading patterns. You are looking at these charts within a week of creation of this addition to my knowledge base. But, at least now we have a measurement platform to begin the discovery process.

RADIAL QUALITY AND CONSISTENCY OF GOLF SHAFTS

By Russ Ryden, A Golf Digest America’s 100 Best Clubfitter
Fit2Score, Dallas Fort Worth, Texas

I made a video about shaft alignment and the feedback I received prompted me to take a hard look at the issue.  I learned from discussions and research that the concept of SST Puring was Approved by the USGA soley as a method of identifying the orientation of a shaft that would cause it to play as if it was round.  There is a USGA rule that says a shaft should be round.  During the time when the SST system was developed this was not always the case.  It was discovered that if a shaft had significant radial stiffness anomalies, it could be oriented to created a tendency for the face to come to impact open, or in another orientation closed.  This is contrary to the USGA’s rule. The process was approved to compensate for manufacturing tolerances of the time.  Today, with most shafts essentially ’round’ to start with, shaft alignment brings nothing of benefit to the golfer.

With the shafts we see today, the simple rule is if you have a shaft that needs alignment, it should be in a dumpster not in a golf club. Most of today’s premium shafts are functionally round, but not all. Even some of the ultra-premium shafts I have measured do not pass my simple quality check.

There is a simple way to test a golf shaft.  It requires a weighted laser pointer and a frequency device with a good clamp.  Club makers know that a shaft can be rotated in a clamp to a position where it will oscillate on a flat line. Approximately 90 degrees from that point is another position where a second flat line oscillation can be found.  These two spots represent the hard and soft planes of the shaft.  A presentation of a study of several shafts can be seen at this Fit2Score article: “Radial Profiles of Driver Shafts“.

The radial quality of a shaft can be determined by comparing the frequency of the strong and weak planes.  If the numbers are the same, or within 1% of each other, the shaft is excellent. High quality tour grade shafts will have very little or no difference.  Consumer grade shafts can have as much a 2% difference. The shaft in this illustration had a 3% difference. In my test equipment, 258 vs 266 CPM, a difference of 8 CPM. The difference between the strong plane and weak plane was a stiffness step in this model of shafts.

Lets step back to the origin of using frequency to measure stiffness. It was created by Dr. Joe Braly and his son Kim Braly.  The same Kim Braly whose initials appear on KBS shafts.  In that system 10 cycles per minute, CPM, represented the stiffness difference between a Rifle 4.5 and a Rifle 5.5.  In that system 10 CPM is a stiffness point. A shaft that is 266 CPM on the hard plane and 258 CPM on the soft plane is an R flex on one side and an S flex on the other.  A 1% difference on that shaft is 2.6 CPM .  That qualifies as tour quality.  A 2% difference is 5.2 CPM.  That is the limit of acceptable quality for a recreational golfer. Beyond that, the shaft is an R flex at the top of the backswing, an S flex at the horizon where the toe is up, and an R flex at impact where the toe is out.  Or turn it around, S at the top, R at mid downswing and S again impact.  That shaft belongs in dumpster, not in a golf club. This shaft is not usable in a driver with a rotating hosel tip. It cannot be re-orientated without causing a significant change of stiffness. It will perform differently at different orientations. 

Range Testing

Mark Maness, our DFW Iron Byron did some testing that gave some interesting results. I had two shafts that were identical in every respect, same make, model, weight, & flex. One had no difference in CPM from hard side to soft side. The other had an 8 cpm difference. During the test, neither of us knew which shaft was which. They were 70 gram S flex shafts. Mark was playing a 70 gram X flex of a similar design. The shafts were set in the standard position then turned 90 degrees, delofting the head 1.5 degrees. This put the soft plane then the hard plane toward the target line. This was repeated on the second shaft. The results were revealing in more ways than we expected.

The image on the left is of the perfect shaft, on the right the shaft that had an 8 cpm difference between hard and soft planes. You can see the dispersion pattern of the perfect shaft was the same in both planes. On the shaft with the 8 cpm difference there was a significant difference in the two. On the hard side, the grouping was tighter, and on the soft side larger. It just so happened that the hard side was a better fit for Mark the unexpected finding of the test. Being properly fit for stiffness will decrease your shot dispersion.

This test show how important radial quality is when drivers today all have rotating hosels. Unless you are playing with a quality shaft, rotation may have a greater influence on your shot patterns than simply changing loft.