Tech FAQs

Tom Wishon Golf Technology takes great pride in the depth and accuracy of our knowledge about golf club design, performance and clubfitting technology.  This section of FAQ’s represents only a few topics related to golf club technology in our desire to educate golfers with the very best and most truthful information.  We’re more than willing to answer any questions you may have about any aspect of golf equipment design and performance.  To ask any question, send us an email at contact@wishongolf.com and we will be glad to answer.

 

What is C.O.R.? What is CT?

C.O.R. is an acronym for Coefficient of Restitution. It is a numerical expression between 0 and 1.00 that ranks the energy conservation in the collision of two objects. For example, a C.O.R. of 0.00 means that in a collision between two bodies ALL energy is lost. Conversely, a C.O.R. of 1.00 means ALL energy was retained, and thus the collision is termed ‘perfectly elastic’. In the collision between a clubface and the golf ball, the highest COR through to be theoretically possible by golf club engineers is about 0.910. The highest COR that TWGT has designed and manufactured in a clubhead is the 0.890 COR of the model 959OL driver. This driver was designed in 2009 to be offered to Clubmakers to build for golfers who strictly play for enjoyment and do not play in formal competitions. For a golfer with a 100mph swing speed, the difference in carry distance with a clubhead with a 0.830 and 0.860 COR is 5.6 yards. For lower clubhead speeds, the distance difference is less.  For higher speeds, the distance difference is progressively a little more.

CT stands for “Characteristic Time” and is an acronym that represents the test performed by the USGA since 2004 to determine if the spring face effect of a clubhead conforms to the USGA Rules of Golf. Prior to 2004, the USGA performed an actual COR test to determine spring face conformity that involved firing a golf ball at the center of the clubface with an air cannon at a speed of 109 mph. If the speed of the ball rebounding off the face was greater than 83% of the impact speed of the ball, the clubhead would be ruled as non-conforming because the COR would be higher than 0.830.

In 2003, the USGA determined that their existing air cannon COR test took too long to set up and perform. Companies that had submitted clubheads for spring face conformity ruling were having to wait 3-4 months to receive a decision so the USGA created a different type of test to determine the same spring face effect as COR which they called CT for Characteristic Time.  However, this CT test is only applicable to drivers.  For testing spring face conformity of fairway woods, hybrids and irons, the USGA employs the air cannon COR test.

In the CT test a pendulum with a steel ball at the end with internal electronic sensors is allowed to swing down and contact the center of the clubface. The sensors measure the amount of time the steel ball is actually in contact with the face before rebounding. A face contact time of 257 microseconds is equivalent to a COR measurement of 0.830. Thus any clubhead recording a CT measurement higher than 257 µsecs indicates the head is non-conforming; heads with a measurement less than 257 are ruled to be conforming.

What is the difference between a variable thickness and uniform thickness clubface?

Since the late 1990s, some companies have elected to manufacture the faces of some of their woodhead models to be slightly thicker in the center than around the perimeter to create what is called a “variable thickness face.” Tom Wishon was one of the very first in the golf industry to experiment with a variable thickness face design on a titanium driver in 1997.

Other companies design the face of their clubheads to be the same thickness over the entire face area, thus making what is called a “uniform face thickness.” In any clubface, the maximum point of face deflection is dead center in the geometric center of the face. Impact at any position other than the center will result in less flexing of the face, and with it, a lower COR, lower ball velocity and a lower “smash factor” (ball speed ÷ clubhead speed). By making an area of the center of the face to be slightly thicker than the area all around the edges of the face, the goal is to allow impacts that are slightly off center to experience more face flexing than the same off center hit with a uniform face thickness design.

To make this premise successful, the face has to be designed in such a way so that the thin outer areas are thinner than what would survive impact were that thickness used in the center, while the center area is thicker than what would be the proper thickness required to result in an 0.830 COR. Computer modeling with an in-depth impact testing regimen is typically required to select the right combination of how thick the center vs the outer edges of the face should be, how large the thicker area should extend out from the center, and how the transition of thickness change should be made. This is the reason the variable thickness face designs of TWGT wood and iron heads are made by high precision CNC machining and not simply by forging or stamping.

Why are the Fairway Wood Lie Angles More Flat than the Driver Lie Angles on Most of Your Sets of Woodheads, when the Standard for Decades has been to make Driver Lie Angles more Flat than Fairway Woods? Why are Most of the Big Golf Companies' Drivers made with a More Upright Lie Angle than your TWGT Driver Designs?

The longer the length of a club, the more the shaft can “droop downward” under the effect of the golfer’s downswing characteristics. Drivers are usually the longest club in the bag, and also possess the most flexible shaft of all. In the former days when drivers were made with a flatter lie (55°) than the fairway woods, the standard driver length was 43″.  Today, most drivers are made to be much longer which increases the amount of downward “droop bending” the shaft will undergo in the swing.  Therefore, to counteract the greater “droop bending” of the shaft in the driver, the driver lie angle is made to be more upright.

We at TWGT design our drivers with a lie angle of 58° as opposed to most of the big companies’ drivers at 60°.  The reason we design our drivers with a lie that is 2° flatter is because we set up our driver headweights to achieve normal swingweight ranges for driver lengths no longer than 45″.  The big companies create their standard driver lengths to be on average between 45 1/2″ and 46 1/2″.  So at the shorter driver lengths we ordain for our driver designs, there will be a little less “droop bending” of the shaft, and hence the need for a little flatter lie angle.

Fairway woods are typically at least 1” to 3” shorter in length than the driver, depending on the fairway wood head number. Typically, the shaft installed in fairway woods will be tip trimmed more than the same shaft installed in the driver, thus making it a little more stiff than the driver shaft. Also, fairway woods are more often hit “off the deck”. This requires the sole to be closer to parallel with the ground to ensure a more solid impact. By making the fairway wood lies a little more flat than the Driver, this aids in allowing the point of contact between the sole and the ground to be closer to the center of the sole.

Why is the Face Thickness a Different Dimension for the Various Driver and Fairway Wood Models, such that some Drivers are Thinner than Other Drivers, or some Fairway Woods are even Thicker than some Drivers?

The right Face Thickness for each woodhead (and thin face irons like our 770CFE and 870Ti) to ensure the maximum face deflection for higher ball speed is determined by several factors – 1) face material strength, 2) face material elasticity (modulus), 3) face height/width/shape, 4) loft angle, 5) bulge and roll – each which interact with each other to ordain how much the face will flex inward for any given impact speed. Therefore, the final face thickness is a combination of these factors times each other to achieve the highest COR for each individual design! Add in the fact that faces can be designed to be variable or uniform in thickness and you compound the determination of the final face thickness even more!! TWGT has designed more thin face clubheads than any other company in the entire golf industry so our experience in creating clubheads with the best face thickness design for best impact performance is truly unequaled.

The custom computer modeling program we have used in our face modeling work takes all of these factors into account to make its recommendation for what the face thickness should be to both survive wear and tear while maintaining the desired COR level. Here is a short version of how some of these factors are taken into account to determine face thickness. The higher the face material strength the thinner the face could be. But as face area increases, the same material has to be thicker than if the face area is smaller. As the loft increases, the face can be thinner because the greater loft means less stress exerted on the face from impact with the ball. As elasticity of the face material decreases, the face thickness for any strength material has to increase to prevent the face from flexing too much and permanently deforming. And as bulge and roll become more curved, the face thickness for any material strength can decrease, since the greater curve across or up and down the face resists the deflection of the face.

As a result, it is possible that a Driver with normal face size made with a very high strength/high elasticity material, can have a thinner face than a small face area Fairway wood made with a lower strength material, when normally you might think the much smaller face of the fairway wood should cause it to have a thinner face than the driver. Sound confusing? Not if you remember the relationship of each factor to how much the face can flex.

What is the best combination of impact launch parameters for a golfer?

The answer depends on the swing speed and swing angle of attack possessed by the golfer and how those swing elements react to the design of the clubhead, shaft and assembly specifications. For maximum CARRY distance, the golfer wants to achieve a combination of launch parameters that would deliver the highest launch angle with the lowest amount of backspin with the highest ball velocity AT THE SAME TIME. And therein lies the rub, as Shakespeare used to say.

It is easy to increase launch angle by increasing loft, moving to a more rear-CG location in the clubhead, or using a shaft with a softer overall flex/softer flex tip section. But these changes on their own will typically bring with them a decrease in the ball velocity and an increase in backspin at the same time. So the net result could be a loss of distance if the drop in ball velocity + backspin increase cancels out the increase in launch angle.

Launch Angle is the easiest parameter for a clubmaker to change for a golfer and see immediate results in the flight of the ball. Backspin reduction is the hardest because so much of that parameter is tied directly to the swing movements of the golfer, which at best require a lot of instruction and commitment to practicing the swing changes necessary to prevent backspin from being too high. That leaves Ball Velocity.

What are ways to increase ball velocity at the same time you increase Launch Angle? A driver head with a higher COR than what the golfer is currently using is one way. Another is to switch to a more flexible shaft or more tip flexible (soft tip) shaft before increasing clubhead loft, because a change in shaft that also changes trajectory will not normally lower the ball velocity at the same time. A shaft that increases launch angle may add backspin but normally if the player is using a higher COR driver head AND has a higher launch shaft, those two factors will more than overcome the decreasing effect of the greater backspin. But never forget that because so many golfers with a driver swing speed under 90 mph are not able to generate aerodynamic ball flight, many times for slower swinging players a launch angle increase simply from a higher loft driver will keep the ball in the air long enough to generate greater carry distance.

The best way to predict the best combination of launch parameters for each golfer is to use TWGT’s proprietary Trajectory and Ball Flight modeling software. The program is easy to use and is accurate for predicting the launch angle, backspin and ball velocity from any combination of loft, shaft bending, COR, headweight and climate conditions.

What does the term “Bend Profile” mean with respect to shaft design and fitting?

The bend profile of a shaft is the distribution of its stiffness over the entire length of the shaft. This is different than the “overall flex” designations of L, A, R, S and X used by most shaft companies. The overall flex is certainly a product of a part of the bend profile, notably the stiffness design of the butt and middle sections of the shaft, and not the tip section.

Have you ever heard the terms “butt stiff” or “tip flexible”, for example? These are non-specific generic descriptions of a part of the bend profile design of a shaft. If a shaft is referred to as being a “butt stiff” shaft, that means the butt section area of the shaft is designed to be more stiff than the butt section of other shafts of the same or similar overall flex. Likewise, if a shaft is said to be “tip flexible”, that means the tip section of the shaft is created to be more flexible than the tip section of other shafts of the same overall flex.

Bend profile can be measured by taking either frequency, deflection or EI measurements at specific locations along the length of a shaft. By comparing these multiple measurements of one shaft to those of another, it is easy to see where and how much the bend profile differs between the shafts. Bend profile analysis like this can be easily compared using TWGT’s Shaft Bend Profile Software so that Clubmakers can more clearly express and predict the bending feel and trajectory differences between shafts of different design.

Why are some of your Driver designs made with a Hook (aka Closed) face angle while others are Square?

Different strokes for different folks! Actually, because the vast majority of golfers who hit the ball crooked on a regular basis tend to push or slice more than hook or pull, when we design a Driver model that we intend to be fit more often for the middle to higher handicap player, we tend to design those models with a hook face angle, with the belief that face angle specification will satisfy a higher percentage of golfers. On driver models we aim at the more accomplished player because of its CG, loft or shape specifics, we tend to design the face angle to be square.  More often than not, this ends up dictating that lower lofts on drivers are designed with a square face angle, while higher lofts will be designed with a slight hook face angle.

No company regardless of size can design enough variations in driver size vs. face angle options to fit all golfers you may encounter in your clubmaking. Therefore, we do try to offer you options in face angle design that will allow you to be successful in your custom driver fitting the highest percentage of the time.  However, through TWGT’s Hand Select Service, clubmakers can request specific loft, face angle, and headweight specifications that can be +/- 1° or +/-2 grams different than the design specification.  We in turn can measure through as many heads as it takes to usually find the specific specifications requested for the clubmaker’s client.

What do the various numbers and letters that are used to describe metals in clubmaking mean? I mean things like 10-2-3 Titanium, SP700 Titanium, 1035 carbon steel, 17-4 or 431 Stainless Steel, and so forth?

Some of these numerical designations for metal alloys makes sense and some of it may be part of the metal supplier/manufacturer’s own brand name for the material. To start with, several countries have their own system of naming/classifying metals which can also make this a little more confusing. For example, SP700 and DAT51 are both Japanese designations for Titanium alloys so the naming convention is from their own country’s system. Russia has their own material nomenclature system and so too does the US.

The US system is somewhat more universally used and consists of the numbering system for which we are more conversant like 10-2-3 Titanium, 1035 Carbon Steel, or 17-4, 15-5, 431 Stainless Steel, to name only very few for example. In this nomenclature the numbers represent the percentage of particular chemical elements by mass that are used in combination to create each specific alloy. By no means does this system reveal ALL of the chemical elements in a metal, but simply the ‘important’ ones that account for the main characteristics of the material.

The American Iron and Steel Institute (AISI), which inaugurated this system, uses a very clear, defined method of explanation for this nomenclature. In their 4-digit system for classifying all Carbon Steel alloys, the alloys which are most commonly used to make forged irons, the number 1 means the metal is a carbon steel. The second digit of 0 or 1 refers to the processing method for making the carbon steel alloy, which is not important for this explanation. The last two digits confirm the percentage of the element Carbon in the alloy, such that 1035 means the alloy contains between 0.32% to 0.39% Carbon with the base metal Iron (Fe) and other trace elements.  1075 carbon steel then means the alloy has between 0.72% to 0.79% Carbon.

In the world of stainless steel, the numbering system you have seen to describe some of the popular alloys does directly represent the percentage of the key chemical elements in the material. For example, 17-4 means a steel alloy with not more than 17% chromium and 4% nickel, 15-5 is 15% chromium and 5% nickel. But then, oops, there are deviations too, such as the case of 431 steel so commonly used for investment casting ironheads, where the alloy consists of 15% chromium and 2% nickel!

In the world of titanium, clubmakers are most familiar with grades such as 10-2-3 (10% Vanadium, 2% Iron and 3% Aluminum), 15-3-3-3 (15% Vanadium, 3% Chromium, 3% Aluminum, 3% Tin) or 6-4 (6% Aluminum, 4% Vanadium). Again, each alloy’s specific mechanical properties such as strengths or elasticity are chiefly ordained by the element make-up, so hence the reason for metallurgists to know these designations when choosing an alloy for a particular use.

There are other organizations in the US such as the ASTM, or SAE and others, who have developed their own methods of nomenclature for naming alloys. Thus, at the end of the day, the only way you can really decipher a metal alloy name/code is to research the material and mechanical property specifications for each alloy from the company that made it. MOST IMPORTANT for clubmakers to remember is that just because you see an alloy name listed with a particular clubhead design does not in any way assure that the head is either made with that alloy, that it is the best alloy for that specific shape and design, or that it the alloy has been processed properly for its use in that particular head design. While TWGT will never profess to know everything about metallurgy, we do believe strongly that our design and engineering experience has allowed us to become very skilled in selecting the right alloy for each specific clubhead design to ensure the desired performance and function of the head.

Click here to learn more

After the metal is forged, cast or otherwise formed into the shape of the clubhead, by no means does that ensure that the material possesses the correct mechanical properties or even the stated properties associated with it. By mechanical properties, we mean things like the yield strength, tensile strength, the hardness, the modulus of elasticity, and many other characteristics of the metal. To achieve their desired final mechanical properties, most metals, after being formed into the part they are being used to make, must be further processed, most commonly by being placed in special ovens to be heated to precise levels of temperature over specific periods of time.

These specific heating processes are designed to very slightly alter the molecular structure of the metal alloy, and from that process, determine the alloy’s final mechanical properties.  For most metal alloys used in clubhead production, typically the higher the heat treatment temperatures used on the metal, the lower the strength, the lower the hardness but the higher the ductility the metal will achieve.

In addition, any one metal can be heat treated in many different ways, depending on what the designer wants the final mechanical properties of his part to be. For example, clubmakers might be very familiar with the high strength steel alloy called Carpenter 455 that has been used to form the faces of a lot of metal woods in the past decade.

In the strip form most commonly used to make a woodhead face from the 455 steel, if you simply weld the plate to the head with no heat treatment (as formed) the steel only has 135,000psi yield strength, is very ductile at 18% elongation, and has a lower hardness of Rockwell C33. Not really a high strength steel at all since 17-4 stainless steel typically has a strength of 135,000 psi!

On the other hand, if you subject the part made from the 455 steel to a heat treatment process that starts by baking the steel at a temperature of 900°C (1650°F), the yield strength of the alloy jumps all the way to 250,000psi and the hardness increases to HRC51 !

Interestingly, the processing of specific heat treatments which may only vary by 50 degrees Celsius (and of course time of heating as well as the cool down or quench are important too) can result in completely different final strength, hardness, elasticity and other mechanical properties. Heat treatment is ALL IMPORTANT in determining the final performance of virtually any alloy used to make a clubhead. Therefore, it is critical for quality that the clubheads you use for your clubmaking are designed and manufactured by reputable companies, because no clubmakers will ever be able to test the heads they buy for these properties.

Heat Treatment Differences for Carpenter C455 Steel Alloy

Heat Treatment Condition

Yield Strength

Tensile Strength

Elongation

Hardness

Annealed Only

135,000 psi

160,000 psi

18%

C 33

Heat 900C

250,000 psi

260,000 psi

8%

C 51

What determines how you choose the various dimension specifications for an iron design, such as toe height, heel height and blade length?

The answer to this is again, a combination of the desired design performance along with the desired visual look of the clubhead when placed in the playing position behind the ball. TWGT designs all of its clubhead models to dimensions and specifications that we determine and clearly specify to the foundry. In addition, we do all of our designing in Metric specifications for dimensions because the progressions of size change from one head to the next are much easier to envision and define in millimeters than decimal inches.

Clubhead weight is the major controlling factor for the dimensional specifications of a head. This is the main reason the longest iron in a set is the smallest in overall head size while the wedges are the largest. Because ironheads have to increase incrementally in headweight to satisfy the typical swingweight to length assembly of the clubs, making each iron slightly larger in overall dimension from long to short is how this weight increase is most typically accommodated.

Center of Gravity location, Moment of Inertia of the head, sole width/design are the three main performance elements which are also controlled by the dimensions of the heads in a set of irons. In an iron, the larger the head, the higher the MOI will be. However, the depth of the cavity in the back of the iron also has a key bearing on the MOI of the head because deeper cavity backs can be made larger in overall size and still deliver the head at the correct weight.

The wider the sole of the iron, the smaller some of the other dimensions of blade length, blade height, heel height or face thickness will have to be on the head, again because of the desired headweight for each head. Here again, the depth of the back cavity can be a controlling factor as well, since the more shallow the back cavity, the less mass can be used in finalizing the sole width. Muscleback irons will almost always be smaller than cavity back irons in overall dimension because of the greater amount of weight used up in the solid, no-cavity back area of the head.

In locating the desired CG position, there is an old saying in head design that guides the process: “Where goes the mass, there goes the CG.” Hence, shorter blade height means lower CG; taller means higher CG. Longer blade length means lower CG because lengthening the head means lengthening the sole, which carries a large amount of the mass on the head to begin with. Wider sole also means lower CG as well as farther back CG. But the chief means of moving the CG farther back is by increasing the offset of the hosel. Knowing all these relationships is what can allow one designer to achieve a certain CG and MOI for the head.

A typical progression for the toe height from head to head in a set of irons is 1mm, for the crotch height it is 0.5mm and most often the blade length stays the same for each head in an iron set. We say typical, because there are cases we may progress by more or less or even keep certain adjacent heads in an iron set the same blade dimensions.

Using only the #5-iron dimensions as an example, an average #5-iron in a set of cavity back irons today would have a toe height of 54mm, heel height of 32mm and blade length of 80mm. Granted, there are #5-irons in sets today that range in toe/heel/blade dimensions from 50mm/28mm/78mm up to 60mm/38mm/84mm. What the overall size is to be is in the mind of the designer and what is intended in terms of looks and playability combined together. But obviously if all the #5-iron headweights are in the range of 250 grams to 264 grams (most common is 253g) the bigger #5-ironheads have to thin out some dimensions and the smaller ones thicken some up, to allow the larger head size end up the same desired weight.

Why do you design your iron sets with the headweight of the PW higher than the #9-iron?

Typically, the PW has been assembled to the same playing length and swingweight as the #9-iron. However, today there are companies that make their PW 1/4” to ½” shorter, and in some cases a few swingweight points higher than the #9-iron. In other words, some customization of the PW compared to the #9-iron has become more common in clubmaking today. We establish the headweight of our PW heads to be 3-4grams heavier than the #9-iron to give clubmakers the most custom assembly options. With our higher headweight spec for PW heads, f you choose to make the PW the same length as the #9-iron, using the same shaft and grip the swingweight for both the PW will be about 2 swingweight points higher in the initial assembly swingweight.

Note that this does not automatically mean the FINAL swingweight will be higher because depending on the shaft weight, grip weight and desired final length, you maybe adding weight to the #9-iron anyway to achieve that final desired swingweight. In this case you still would have the option to make the PW the same length as the #9-iron AND still be the same swingweight. In addition, if you wish to make the PW to be 1/4” to ½” shorter than the #9-iron, the extra 3-4 grams of headweight in the PW gives you the option of making the swingweight the same as the #9-iron.

From a fitting and playability standpoint, TWGT does recommend that the swingweight of the PW be made to be 2 swingweight points higher than the swingweight of the set. The reason is because most of the time and unlike the #3 – #9-irons, the PW is being swung at less than a full swing. When the PW is used for a three-quarters swing down to chip shots, a higher headweight feel can help make the rhythm of the slower and shorter length swing to be more consistent.

What is the difference between a Titaniumwoodhead that is made from multiple pieces welded together compared to one that is made by investment casting, or forging?

Titanium driver heads are made in a variety of construction methods – 2-piece, 3-piece, and 4-piece forged, 2-piece, 3-piece, and 4-piece plate-formed,2-piece all investment cast, 1-piece investment cast body + plate-formed face, 1-piece investment cast body + true forged face, are just some of the methods employed to make Titanium driver heads.

When Titanium woods first hit the US market in 1993, almost all were made by 2-piece investment casting. The face + body was one cast piece, the sole plate piece the second, and the two were vacuum welded together to make the finished head. Only a few foundries could produce them because the cost of the vacuum casting furnace required to cast Titanium is incredibly expensive. With high demand for Titanium driver heads all through the 1990s, the 3-piece and 4-piece plate-formed construction method soon followed. The number of factories offering 3 and 4-piece Titanium driver heads exploded because the cost of tooling and production machinery to manufacture such a head was relatively low.

The other reason plate-formed Titanium driver heads became so predominant is because of their very low reject rate in production compared to the high reject rate of an investment cast Titanium driver head.  Casting Titanium is very difficult because the molten Ti alloys have a viscosity more like molasses than water.  Trying to make the molten Titanium flow completely and consistently into a casting shell with wall thicknesses of only 1mm is incredibly difficult. As a result it is very common to see a reject rate of 20-30% in cast Titanium driver heads.

3 and 4-piece plate-formed Titanium driver heads are made by press-forming Titanium sheet/plate material to make the parts of the head body, with the hosel machined from bar stock Titanium. In a 4-piece, the 1) top plate (crown), 2) sole + perimeter (sole/skirt), 3) the face and, 4) the hosel comprise the four pieces. In a 3-piece the hosel is formed in one piece with the face, then joined with the sole + sides and the top plate to reduce the number of pieces by one.

The key elements to a quality 3 or 4-piece Titanium woodhead are in two areas – first in the selection of the proper alloy of the Titanium sheet material for the design shape/size, and second, the quality of the welding of all of the 4-pieces together to form the finished head.

Welding Titanium is a very tricky proposition because Titanium in its molten or welded state is extremely reactive to oxygen. Exceed the minimum oxidation threshold of Titanium welding and the result can be cracking of the head at the seams when the club is used in play. In our career experience of designing more than 100 different Titanium driver head models alone, and visiting/consulting with many different Titanium head-making foundries/factories, we have seen a lot of different welding methods employed by foundries, many which were very suspect in their quality. As a result TWGT will only contract with two factories to perform the welding of any Titanium driver head we design, regardless of the head construction method.

The net result is that the difference between any of the methods of constructing a Titanium driver head is first in the design and then in the quality of the manufacturing process. The 3 and 4-piece heads, if made properly, produce as good of a Titanium woodhead as there is, with the key being watch-dogging the manufacturing processes closely.

From the mid-90s to the late 2000s, most of the big golf club companies produced their Titanium driver heads by investment casting rather than through the 3- or 4-piece process.  This was because in the huge production volume requirements of the big companies, they were quite scared of the potential for head cracking due to the greater amount of welding that has to be employed in the production of a 3- or 4-piece head versus an investment cast head.

However, in the late 2000s virtually every one of the large golf companies began to switch fully from investment casting their Titanium driver heads to producing them by the 4-piece method.  This change came about because of a change in the method of making the 4 parts of the head which allowed robotic welding to be used to ensure a higher level of quality in the welding instead of human welding. 

There are so many different Titanium alloys that are used to make drivers these days. What is the difference between them and is there one over all others that is best for performance?

First of all, the performance of any Titanium alloy in a driver head is not so much in the make up of the alloy as it is in HOW the alloy was used in the design of the head. If the face of the driver is engineered poorly in terms of a face thickness that is too thick or too thin for the size/area/loft/bulge/roll of the face, then the entire potential of the alloy would be completely wasted and the performance of the head could have been exceeded by a well engineered Driver that was made from standard 17-4 stainless steel!

Titanium alloys are used in primarily two areas of application where the unique characteristics of these metals justify their selection. Either you want your object to be larger in size while being light in weight, OR, you want to take advantage of the high strength to high elasticity characteristic possessed by Titanium alloys. For golf clubhead design, both are reasons for the use of Titanium alloys. Titanium alloys have a 40% lower density than steel, which means they are significantly lighter per volume area than steel alloys. Titanium alloys are also stronger than most of the low cost steel alloys, and they have far superior elasticity to all steels. In terms of combining strength to weight to elasticity all together, Titanium is superior to almost any steel alloy, hence it is better in strength to weight to elastic efficiency.

To get to the point of the question, with the number of different Titanium alloys being used to make the faces of today’s large, 430 to 460cc Drivers, it is very easy to make the face achieve a COR of 0.830 with virtually any Titanium alloy. For most companies, it is a waste of money to use a high grade Titanium alloys such as 10-2-3, 15-3-3-3 or SP700 to make the face, because the COR limit can be achieved easily in a 380cc size head or larger using 6/4 Titanium.  Since 6/4 Titanium alloy has a much lower cost than any of the other higher strength titanium alloys, most companies stopped using these more sophisticated alloys in their driver head design in the early 2000s.

However, if the driver is designed with some other performance factor in mind such as a different weight distribution or a higher MOI, it is possible and often preferable to use a higher strength Titanium alloy for the face.  By so doing, it is possible to make the face thinner than it would be using 6/4 so the face would comprise less weight that can be used elsewhere in the head to accommodate the designer’s goal for the MOI or center of gravity location while still being able to keep the COR within the rules of golf.

Why do some Titanium driver heads sell for less than $50 while others sell for well over $100?

Lots of factors enter into the answer, among them the cost of the materials, the cost of the manufacturing process used to make the head, the quality of the head design, the quality control steps in the manufacturing process, and the profit requirements of the foundry making the head as well as the profit requirements of the company selling the head.

A chief factor is the cost of the materials and manufacturing. A Titanium driver made by true forging the face from 10-2-3 Beta Titanium alloy and investment casting the body from 6-4 Titanium will cost over twice as much to make as a 4-piece construction Ti driver made with a 6-4 Titanium face and the body parts from a low strength CP grade titanium. The vast majority of the cheaper Titanium driver heads sold in the component market are made with low strength Titanium for the face and body parts, and as such, will be more susceptible to failure when the head is put into play.

Robotic welding and vacuum chamber welding of the Titanium parts of a driver head (which ensure no oxidation of the welds) will cost a lot more than inert atmosphere hand welding (which will not ensure total non-oxidation or consistent thickness of the welding). True forging from a billet of Titanium will cost a lot more than stamping the parts of the head from sheet Titanium metal. Heat treating in an oven that allows no head to touch another during the process will cost a lot more than piling heads on top of each other in a wire basket placed into the heat treatment oven. X-raying the welding lines or camera scoping the inside of the head to ensure proper joining of the parts costs a lot more than performing no welding inspection. Plus/minus ranges in the specifications of the heads to tight tolerances also accounts for a significant difference in cost. These and many more of the steps in the manufacture of a Titanium driver all factor heavily into the final production cost and overall quality of the head.

In the golf industry today there are more factories capable of making Titanium driver heads than there are orders from golf companies to keep them all busy. Some of these foundries have high overhead because of the investment they have made in production, inspection, quality control equipment and skilled personnel. Others have very little in the way of quality, high-end production equipment or skilled workers. Some foundries are very busy with many customer orders, others are starving and looking for any orders they can make. All of these factors work into the determination of price as well.

Can a quality non-close out Titanium Driver head be bought for $50-$60 or less in the component market? If the only golfers playing Titanium driver heads were players with a clubhead speed no higher than 75mph, the answer could be yes.  But in our opinion based on a lot of experience in designing and managing the production of Titanium driver heads for all golfer’s requirements, the answer is no because there are way too many quality requirements that would have to be sacrificed to get the final selling price of that head to that price level. As a result, the overall failure rate and poor performance incidences of such heads will be far higher than with a quality made head designed and manufactured by a skilled designer and production factory.

Many companies like to list the type of carbon steel used in their forged ironheads. What is the difference between carbon steels like 1030, 1045, S45C, 1050 and others like that, and why are different carbon steels used for forging irons?

The numbering systems used to describe any alloy are determined by each country’s organizations that try to provide standardization for the composition of the various alloys. In the US, the AISI (American Iron and Steel Institute) uses the designation of 10XX to refer to any carbon steel. Therefore, the digits ’10′ always mean the alloy is a carbon steel alloy. The last two digits are used to express the percentage of the element C or Carbon in the alloy. So for example, a 1030 carbon steel has 0.3% Carbon while 1050 carbon steel has 0.5% Carbon in the chemistry of the alloy. The designation of the letter ‘S’ in front of the alloy ID simply means this is a Japanese made alloy of carbon steel, with the last two digits also indicating the percent of Carbon. So an S45C is a carbon steel alloy made in Japan with 0.45% Carbon in the mix with the base material of Iron (Fe).

The higher the percentage of Carbon in the steel, the harder, stronger and less ductile (compressibility in the forging process) the carbon steel alloy will be. In selecting an alloy of carbon steel for a forged ironhead, the following properties of the steel have to be addressed by the designer:

  • Ability of the steel to be formed and compressed in the forging dies
    • All metals can be forged regardless of strength and hardness, but the more force required to form the head, the sooner the forging dies can wear out, the more expensive the steel that has to be used to make the dies to resist wear, the more expensive the overall cost to make the head, and the harder it is to compress out all of the internal pits and voids inside the molecular structure of the steel.
  • Surface hardness to resist marking and ‘dinging’
    • The softer the steel, the more the heads will develop ‘dings’ from the irons banging against each other when the golfer walks or rides over bumps with the clubs on the back of the cart. While the nickel/chrome plating helps reduce this tendency, some designers consider this to be an important point in the selection process of the carbon steel alloy.
  • Ability of the carbon steel alloy to be formed consistently to the desired shape and surface condition before machining and grinding
    • All forged ironheads undergo a lot of surface machining and grinding after forging to prepare them for the nickel/chromium plating process. Within a good forging factory, the softer the carbon steel, the more the alloy can be compressed tightly in the forging dies and the less surface grinding that has to be performed on the heads, which can mean more consistency from head to head. However, this is as much a process of the quality of the foundry’s finishing procedures as it is of the steel composition.

What is the 5-step forging process that you describe you do on your Wishon Golf 555C and 555M forged iron heads and how does that differ from the way other companies make forgings?

The normal forging process for irons consists of 4-steps in the forming of the raw forged head.

1. Heating and bending an angle in the billet of carbon steel to separate the part of the bar that will become the hosel from the part that will become the head or blade within the forging die.

2. Forging or pressing to ‘rough’ out the first general shape of the blade and hosel.

3. Forging or pressing to make the final shape of the head.

4. Trimming off the excess steel that ‘flashes’ out between the two halves of the head’s forging die to finish the raw forging after which it goes on to grinding, machining, polishing and electroplating.

Our 5-step forging process for the 555C and 555M models goes through the same first 4 steps but adds on a 5th step. The raw forging that most companies take on into finishing is heated to slightly soften the carbon steel and then is put into a final forging die where it is more tightly compressed. From this, three things happen that are different from other forged ironheads:

1. The size of the flashing line all around the head is greatly reduced so the grinding process to remove this edge of steel that sticks up all around the head has far less of a tendency to touch the outer surfaces of the head which means much more consistency in the shape and radius profiles of head after head in the production process. As a result, all heads of the same number end up looking exactly the same, instead in some irons where different models of the same head numbers can end up a little different in face profile, leading edge radius, sole radius, etc.

2. The steel is able to be “packed” more tightly into the forging die with this additional forging step. This reduces the amount of the ‘voids’ and ‘inclusions’ which are the little holes in the grain structure of the steel inside the heads, which in turn can slightly contribute to a little more solid feel. Having a high number of these little holes inside the head causes a little tiny bit more vibration, and thus the chance for better feel if you compress and pack the steel more tightly in the head to reduce and eliminate these holes.

3. The surface of the forging is much smoother when it comes from this 5th forging step than it is when it comes from the 4th step. This means less grinding and machining of the head, which means a little better quality in the +/- tolerances for weight.

What makes a good face material for a driver?

The goal of most drivers is to create a head that has the maximum amount of face deflection from impact with the ball. The more the face deflects, the less the ball deforms against the face and the less energy the ball will lose. That translates into a higher ball velocity for any given swing speed, and it is ball velocity that chiefly determines the distance of the shot  (proper launch angle for the golfer’s swing speed and angle of attack is key, but it is second to ball velocity).

The best materials for maximizing face deflection are those that have what is called a high STRENGTH-TO-MODULUS RATIO. The strength of a material can be rated in many different types of tests, but the most important strength measurement related to driver faces is the yield strength. Yield strength is a measurement of how much force is required before the material permanently bends or deforms. But what has to come with a high yield strength to make a good driver face material is a low modulus of elasticity along with high toughness.

Modulus is the measurement of a material’s ability to resist stretching, so the lower the modulus measurement, the more the material can be stretched. In graphite shafts you want higher modulus materials to ensure stiffness, but for a driver face you want to have a low modulus material. If you have high strength and low modulus together in the same material, you have a good candidate for a face design that will deflect inward a lot before it reaches a point of permanent deformation.

Toughness is the ability of a metal to rapidly distribute within itself both the stress and strain caused by a suddenly applied load, or more simply expressed, the ability of a material to withstand shock loading. It is the exact opposite of “brittleness” which carries the implication of sudden failure. A brittle material has little resistance to failure once the elastic limit has been reached. There are many materials that have a higher yield strength than titanium, most notably high strength steel alloys like Carpenter AerMet, Carpenter 475, 465, 455 and T275 to name a few. But steel alloys always have a much higher modulus of elasticity than do titanium alloys, often being as much as two times less elastic than titanium alloys.

Therefore, a titanium alloy can be as much as 30-40% lower in yield strength than a high strength steel but makes up for that with its modulus being over twice as elastic as the modulus of the high strength steels. However, there are some high strength steels that can make driver faces with as high of a COR as any titanium alloy. This happens because if the strength of the steel is VERY high and the toughness is good, the very high strength allows the face to be made much thinner than ever possible with any titanium alloy, which in turn allows the ball to deflect the face inward the same or even a little more as the titanium alloy. It is the amount of face deflection that makes the COR high and the swing speed to ball speed ratio high as well for more distance.

What makes a good face material for a fairway wood or an iron?

As with driver heads, titanium alloys would be the best candidate.  However, most companies do not choose to design fairway woods and irons with a titanium face because of its much higher cost.  Golf companies have learned over the years that golfers will pay the higher cost for a titanium driver, but not for fairway woods or irons.  The reason is chiefly because with a driver, the golfer is buying ONE higher cost club but with the fairway woods and irons, the golfer knows he has to buy 2 or 3 woods and 7 or 8 irons so the total cost is much higher.

As such, when a company wishes to design a high COR fairway wood or iron, they look for high strength steel alloys which all carry a lower cost than titanium alloys.  As mentioned in the previous Q&A about titanium driver faces, it is possible to make a clubhead with a high COR using a high strength steel alloy for the face.  Steel alloys are available which have a yield strength double that of titanium.  Therefore, even though the modulus of elasticity of all steel alloys is not as “stretchable” as for titanium alloys, with the yield strength of some steel alloys being double or more than titanium alloys, it is then possible to make the steel face very thin to allow the face to flex inward to the point of achieving a high COR without fear of the face caving in.

However, it is true that in a perfect world in which golfers did not balk at the price of golf clubs, using high strength/low modulus titanium alloys for the faces of fairway woods and irons would definitely push their performance to the maximum level possible.

How does the actual spring face of a driver work to increase ball velocity? Is it like a 'slingshot' where the face flexes back and then snaps forward to launch the ball?

Not at all, despite the fact a lot of golfers think this is how it works. In the collision between the ball and the face there is a lot of energy that is lost. Approximately 80% of the energy loss comes from the ball squashing against the face, while the other 20% of the energy loss comes from the face deflecting inward. A good spring face works to increase ball velocity because it allows the face to lose a little more energy by deflecting inward more, which then allows the ball to lose a lot less energy by deforming or squashing less against the more flexible face. So the whole key is to let the face flex more so the ball deforms less and the result is a higher ball speed off the face for any swing speed. And the higher the ball speed, the greater the distance will always be.

How much does a face deflect inward when it is made to be thin?

The more the face deflects at impact without caving in the face, the higher the ball speed will be in relation to the swing speed. (aka the “Smash Factor”) The amount the face deflects inward on a driver is determined by a lot of different factors, all working in combination with each other:

1. Swing speed – the faster the head speed the more force imparted to the face, and potentially the more the face could deflect.

2. Face Area/Size- the larger the face area, the more potential exists for the face to deflect more.  This is why it is easy to make drivers with an 0.830 COR face, but much more difficult to do that with fairway woods, hybrids and irons.

3. Bulge and Roll – The more curved the face radii on the driver, the more ‘structural’ resistance there will be to the face deflecting inward.

4. Loft – The less the loft, the more force the face is subjected to and thus the more the face can possibly deflect.

5. Face Material and Face Thickness – The higher the strength to modulus ratio of the metal from which the face is formed, the more potential for face deflection, but only if the face thickness is engineered to match properly with the strength to modulus ratio. This is why some high strength steel faces are much thinner than faces made from titanium, yet in some cases the thicker titanium face could deflect inward more. It is all about how much the face material can “take” in force before it permanently deforms or fractures.

6. Ball Construction – The softer the compression of the ball compared to the swing speed of the golfer, the more the ball will deform and the less the face will deflect.

In terms of actual deflection amounts, for a driver made with a 55mm face height with the face properly engineered from a beta titanium alloy with good strength to modulus ratio, the maximum face deflection would be on the order of 0.065″ to result in a COR of 0.830. To contrast, a 44mm driver face height with a 17-4 stainless steel made thick enough to resist failure would only be able to deflect about 0.025″. Hence it is possible to see how influential face height can be to the spring face capability of a woodhead.

What is vertical gear effect and does it help improve shot performance?

Most clubmakers are familiar with the action of horizontal gear effect, the reaction of the clubhead rotating/twisting around the vertical axis through its Center of Gravity in response to an off-center hit on the toe or heel side of the face. This is the reason that the toe to heel curvature of bulge is designed on the face of all woodheads. Impact toward the toe or heel causes horizontal gear effect which in turn, tilts the axis of the rotation of the backspin (also called creating sidespin) on the shot so a toe side hit picks up a draw flight and a heel side hit results in a fading ball flight.  Therefore, to counteract this sidespin action on the ball the bulge curvature across the face is needed to start the ball more to the right (toe shot) or left (heel shot) so when the sidespin kicks in, the ball draws or fades gently toward the target area.

There also exists a small rotation of the head around the horizontal axis through the CG as well, which is called the vertical gear effect. When impact occurs high on the face, above the CG, the head rotates very slightly back. Most of this rotation is stopped by the resistance of the hosel + shaft, but enough can happen to cause the backspin to be lower for shots hit higher on the face than it would be for shots hit in the center of the face.

When impact occurs low on the face, below the level of the head’s CG, the head will also rotate very slightly back, but in the opposite direction of rotation than when impact is higher on the face above the CG. Again, most of this rotation is stopped by the resistance of the hosel + shaft, but enough will happen to cause the backspin to be a little higher for shots hit lower on the face than for shots hit in the center of the face.

As the golfer’s driver clubhead speed gets higher and higher from 90mph and on up, a reduction in the amount of backspin can help generate slightly more distance.  This is because at these higher swing speeds, the amount of backspin on a shot is always higher than for lower swing speeds. If a golfer with a higher swing speed generates more than 3000 rpms of backspin with the driver, this much spin has the effect of making the ball fly higher and experience more friction as it flies through the air. This in turn will cause the ball’s angle of descent to the ground to be more vertical. When the angle of descent of the ball is greater than 45*, the ball will not roll very much when it hits the ground. On the other hand, when the angle of descent of the ball is less than 40*, the ball will hit and roll more, thus delivering more overall distance to the shot.

Therefore, golfers with a higher swing speed are better off making contact with the driver a little above the center of the face so the spin rate is a little lower, and with it, the height of the shot is a little lower and the angle of descent of the ball to the ground is less steep to generate more roll. Golfers with a swing speed lower than 90mph do not typically gain much benefit from the reduction in backspin caused by hitting the ball higher on the face. At lower swing speeds, the ball needs more backspin or a higher launch angle to stay in the air longer to carry and fly farther.

In the 1980s shaft torque was talked about a lot as a factor for shaft fitting, while now it is rarely mentioned. Is the torque of a shaft important anymore in shaft fitting?

Shaft torque is not nearly as much of a fitting factor today as we all were led to believe in the 1980s. Prior to the mid-1980s, graphite shaft makers did not know how to make their shafts with a torque much lower than 6-7*. However, by wrapping some of the layers of the graphite pre-preg material around the forming mandrel so the graphite fibers were at a 30-45* angle to the centerline of the shaft, shaft makers were able to start making graphite shafts with a lower torque (more accurately termed greater torsional stiffness).

Once the shaft companies discovered how to make shafts with a lower torque measurement, what followed was a race among the shaft makers to see who could develop the lowest torque possible in a graphite shaft. That seemed logical at the time because being able to reduce the torque in a shaft from say, 7* to 4* did result in more accuracy, especially for golfers with a more forceful, aggressive swing. As more testing followed, we now know that if the torque is too low for a golfer, the result can be a very stiff and boardy feel.

Perhaps one of the best points to verify that some torque has to be designed into shafts is the fact that the vast majority of the players on the world professional tours use graphite shafts in their woods with a torque design which falls between 3 and 4 degrees. As a result, the vast majority of R, S and X flex graphite wood shafts are designed with the torque between 3 and 5 degrees. However, there are a few points that clubmakers do need to keep in mind with regard to torque as a factor of fitting:

1. While on its own a torque of >5 degrees may only cause slight mis-direction problems for very strong golfers with high swing speeds, it is still advisable to advise any golfer with a swing speed over 95mph who also starts the downswing with a strong downswing force not to use shafts with torque of 4.5 degrees or higher. The sudden application of a high downswing force could cause the head to exert a greater twisting influence on the shaft if the torque is higher than 4.5 degrees.

2. Golfers with a slower swing speed and smoother swing tempo are best advised to stay away from shafts with a torque lower than 4 degrees. Again, if other more important shaft fitting factors such as shaft weight and an accurate match of the shaft’s overall flex (butt and tip section stiffness both) are performed for these golfers, the torque alone will not typically cause shotmaking problems.

3. Torque is still considered a contributor to the feel of the shaft.  A shaft with a lower torque may feel more firm overall to the player just as a shaft with a higher torque may feel a little less firm. However, the shaft weight, shaft overall flex and shaft bend profile are still the predominant factors that control the feel of the shaft during the swing with torque standing as a slight additional modifier to that overall flex and weight feel the player may notice.

In the optimization of the launch parameters of launch angle, spin rate and ball velocity, how much can the club itself affect a change in the backspin rate?

One of the myths that seems to perpetuate itself in the golf equipment industry is that all golfers should try to achieve the lowest amount of backspin when they hit their driver.  In addition, a lot has been written to lead golfers to believe if they do hit the ball with too much backspin, a change to a different driver or different ball will solve all their spin problems.

Here are some facts about golfers, golf clubs and backspin.

1.  The higher the loft angle on the clubhead, the more spin will be generated for all golfers UP TO A LOFT OF 58°.  As the loft of the clubhead increases higher than 58°, less backspin is generated.  This is because over 58°, the angle of the clubface has increased to the point that the ball cannot be compressed into the face as much to create the friction between the ball and face that is necessary to increase backspin. The reason most golfers see the ball stop sooner when hitting shots with a 60° lob wedge is because the higher loft generates a steeper angle of descent of the ball when it lands on the green.

2.  The higher the clubhead speed of the golfer, the more backspin will be generated for any given loft.  Higher clubhead speed increases the compression of the ball against the lofted clubface.  This increased ball compression against the face increases the friction between the ball and the clubface, which in turn increases the amount of backspin on the shot.

3.  Golfers with a driver clubhead speed lower than 90mph do not ever need to be concerned about trying to achieve lower spin with the driver.  At driver clubhead speeds lower than 90mph, most golfers actually would hit the ball farther if they could somehow generate MORE backspin with their driver.  The reason is because the ball speed generated by a driver clubhead speed below 90mph is not high enough to allow the ball to achieve full aerodynamic flight to allow the ball’s design properties to keep the ball in flight longer in the air.

In gerneral, a golf ball does not achieve aerodynamic flight properties until it is launched from the clubhead at a speed higher than around 125mph.  Accordingly, it takes a driver clubhead speed of 85mph and higher to launch the ball at a speed of 125mph and higher.  As the ball speed progressively increases, it’s spin increases and the lift under the ball increases to combine with the ball speed to keep the ball in the air longer to fly farther.

In general, excessive spin only becomes a problem with the driver when the ball speed begins to approach 150mph (and higher) with a spin rate of 3000 rpms and higher.  Backspin which gets to the point that it is reducing the golfer’s potential driver distance can be visually seen in the form of a ball flight shape that ramps upward in the air quickly to a higher point, after which the ball falls more suddenly out of the air on a steeper angle to the ground.

4.  Different golf ball designs can have a visible effect ball flight shape and can reduce or increase the amount of backspin a golfer puts on the ball when hitting a shot.  However, their effect is directly proportional to the clubhead speed and ball speed the golfer generates with the shot.  At a clubhead speed of 100mph (ball speed 149.5mph) the typical difference between a high spin ball design and a low spin ball design is in the area of 400 rpms.  As the clubhead and ball speed of the golfer increases, so too does the difference in spin between a low and high spin ball design.  This is why you hear that tour players with their much higher clubhead speeds do see a difference in ball flight shape between different ball designs, but most regular golfers with only slightly above average clubhead speeds do not.