Monthly Archives: January 2016

EI Measurement Refined

Adjusting 3 Point Bend Measurements for Tube Deformation

By Russ Ryden, Fit2Score, A Dallas Fort Worth Club Fitter & Club Maker
The Golf Center at the Highlands, Carrollton Texas

EI profiling is one of several methods used by shaft designers and club fitters to understand a golf shaft. In several research papers on golf shafts, 3 point EI bend testing is faulted for failing to account for tube deformation under load. With the assistance and coaching from Dave Tutelman I began a study of shaft deformation in a 3 point bending test. That study, which lasted over a year, is now complete. I have developed a simple measuring process to compensate for tube deformation in 3 point EI measurements.

These illustrations show a cross section of the shaft measuring process and graphically illustrates the deformation issue.

Understand EI Deformation 1Figure 1:  The typical 3 point measuring system uses a gauge positioned at the top of the shaft. A preload is applied to the shaft, and the measuring gauge is set to zero.

This set of drawings is vastly exaggerated to illustrate the point. In fact the deformation of the shaft is a very small percentage of the bending of the shaft.

 


Understand_EI_Deformation 2Figure 2:
 When load is applied to the shaft, It bends. Golf shafts are hollow tubes, not only do they bend, they also deform, becoming oval. Deformation is a function of the hoop strength of the shaft. In linear bend testing, the oval deformation is a source of error. We want to measure the bending of the centerline of the shaft shown here as 10 units. We actually measure both ovaling and bending.

 

 

Understand_EI_Deformation 3Figure 3:  Remember, In these drawings, the ovalization of the shaft is vastly exaggerated. The top to bottom dimension of the loaded shaft changes by 40 units. Part of that dimension, 30 units is the deformation of the shaft. Not the bending of the shaft.

 

Understand_EI_Deformation 4Figure 4:  The correction; measure both the top wall and the bottom wall of the shaft to calculate how much the shaft deformed. Subtract half of that difference from the top wall measurement. In this exaggerated illustration, the actual centerline deflection is 10 units. That is determined by subtracting half the difference between the top and bottom wall deflection from the top wall deflection.

This deformation occurs in three places, the left support, the center press and the right support. To accurately determine the centerline EI, all three deformations must me measured and accounted for in the calculation of EI.Understand EI Deformation 5

Figure 5:  This is an EI instrument built for researching and understanding tube deformation during 3 point loading. A gauge under the shaft measures deformation at the bottom wall. The difference between the top and bottom gauge is ovalization of the shaft. A third gauge measures deformation at the beam support. After studying many shafts, we can now forecast deformation from hoop stiffness alone. 

ActualDeformationAdjustmentThe ovalizing of the shaft shown above is exaggerated for the purpose of the illustration. In fact it is typically less that 2% near the tip and as much as 20% near the butt. The correction does not change the shape of the EI graphics. It does modify the slope. The butt section of shafts is revealed as stiffer than uncorrected top wall deformation data. As you can see here, the subtle stiffness changes shown in inch by inch 3 point profiling are apparent in both the uncorrected and adjusted graphics. Those stiffness bumps that are the essence of feel and performance are apparent in both graphics. The adjusted graphics make butt stiffness more accurate going forward.

The three gauge instrument shown above is time consuming to use. It is now available for purchase. We knew at the onset of this research project that deformation was going to correlate to the hoop strength measurements we are already taking with a single gauge instrument.

HoopDeformationAdjustmentApplying a multiplier to the hoop deformation we have been measuring, we correct the EI data. In this illustration you can barely see a difference between the 4 point measured deformation and the 1 point + hoop adjusted deformation. The measured deformation is done at both the tip and butt supports and the press. The hoop deformation is done under the press, applying the load to the shaft while it is firmly supported on a block of metal.

A great number of shafts with different materials have been run through the 4 point measurement process. A universal correction factor has been shown to apply universally to all shafts we have tested. Hoop deformation against a solid block is a method that accurately corrects top wall measurement to center line bending. This should forever end the critique of the accuracy of 3 point measurement of golf shafts. I am indebted to my friend Dave Tutelman for his guidance and assistance as we worked on this project for over a year.

 

ACCRA FX Driver Shaft Review

ACCRA FX Driver Shaft

By Woody Lashen Pete’s Golf, Mineola, New York

ACCRAFX2_Image

ACCRA introduced the FX product line in 2015. There are 4 versions, FX1, FX2, FX3 and FX4. The FX line of shafts replaces the Dymatch line for Accra.  Quality has always been excellent in Accra shafts and it moves to the top of the class with the FX line. The FX 200,300 and 400 are made in Japan in a small boutique manufacturing plant.  This divers line allows us to fit many different players in to the FX series.   Accra’s concept was to have one family of shafts but with 4 different profiles. With the FX 100 being the highest launching shaft, FX 200 mid launch, FX300 low launch and the FX 400 lowest.  (Note the 400 only comes in X flex).  Along with each profile there is Fairway woods and hybrid shafts designed to play the same as the driver shaft.  This is rare in the shaft industry; most shafts are designed for drivers only.  Accra found that on Tour it was rare for a player to use the same shaft in there fairway or hybrid as in there driver so they designed a shaft line that would allow the Fairway and hybrid shafts to feel and play the same as the driver.  They had great success with this technology in the Dymatch series and the FX picks up with they left off, but even better quality.

ACCRA FS1 EiGjTbThe ACCRA FX1 series is a high launch design. That can is seen in the tip to butt rations as well as in the calculated butt loaded deflection graphic show above. They are not as stiff as the FX2, 3 or 4 models, by design. Roundness, or radial consistency averaged 99.0% with a 0.6% standard deviation. Balance is neutral.

The 100 series fits best for slow to medium speeds and tempos.  With 3 weight options for the driver it covers a lot of players.

ACCRA FS234 EiTbMadeInJapanThe ACCRA FX2, FX3 and FX4 bear the notation Made in Japan. They follow the ACCRA CS1 as premier examples of how attention to detail will create shafts that are consistent and orderly progressions from weight to weigh and flex to flex. A golf club fitters dream set of shafts. Roundness of the review samples averaged 99.5% consistency with a 0,2% standard deviation. By design, they launch lower than the FX1 series.

As speed and tempo rise the 200 and 300 come more in to play or those needing medium launch.  The 400 is only for the rare player with high speed and tempo, however that player will really enjoy its stability.

Woody Lashen co-owner of Pete’s Golf talks with Gawain Robertson co-owner of Accra Golf shafts talk about the FX series shafts.