Effects of Clubhead Features:
Material and Manufacturing Process

There are quite a few dimensions to the choice of material for a clubhead:

• The "feel" of the clubhead.
• The distance the clubhead can hit the ball.
• The weight of the clubhead, or the peripheral weighting (forgivingness) that can be achieved.
• Maintenance required for the clubhead.
• How much can the clubhead be adjusted to achieve different playing characteristics (e.g.- bending for loft and lie).

Playability: Feel

There has been a lot of controversy about forged vs cast heads, or stainless steel (the usual cast clubhead) vs chromed carbon steel (the usual forged clubhead). On the basis of the published results of some controlled tests, I believe that material has very little to do with it. The difference is mostly in the design of the head. That is, usually

Forged	=	Carbon steel	=	"Muscleback" blade
Cast	=	Stainless steel	=	Cavity back

The few studies that played mix-and-match with these relationships (for instance, cast stainless musclebacks) came away concluding that the difference in "feel" was really the difference between a cavity back (big sweet spot) and a muscle back (small, critical sweet spot).

Still, a lot of golfers seem to believe that a softer clubhead material changes the feel of the club, and there are manufacturers out there encouraging this belief and producing clubheads to sell to it. So let's analyze whether there's anything at all to it...

The "softness" of feel is a combination of the softness of the clubhead and that of the ball. More precisely, the softness of feel is the inverse of the total stiffness of the collision between ball and clubhead. Stiffness is measured as a force divided by the deflection (in this case, the compression) produced by the force, designated "force/deflection". The lower this ratio (either due to reduced force or a longer compression), the softer the collision feels.

During impact, both the ball and the clubhead compress. Consider the compression stiffness of each of the two materials:

• Force/deflection for the clubhead material is Kh.
• Force/deflection for the ball is Kb.

In an "elastic collision" like that of the ball and clubhead, the overall stiffness of the collision is:

		1
Force/deflection overall	=
		1/Kb + 1/Kh

Of course, steel -- any kind of steel -- is much stiffer in compression than a golf ball. That is, Kh is greater than Kb, by a factor somewhere between a hundred and a thousand. Let's assume it's 100, just to give the greatest possible chance to show that clubhead material does matter. Even with this assumption, a few examples will show us that the stiffness of the collision is dominated by the ball's construction, not the clubhead's.

• From the softest steel to the hardest, the range of Kh is only a 10% range. Suppose forged carbon steel were a full 10% softer than cast stainless. Then wouldn't the collision feel 10% softer? No, it wouldn't. From the equation, a 10% reduction in Kh results in only a 0.2% reduction in overall stiffness of the collision.

• Well then, let's choose a really soft metal like copper, and use it as an insert. (As I write this, such a set of irons has appeared on the market.) Even copper, at only half the stiffness of steel, results in only a 1.0% reduction in the overall stiffness of the collision. Not even the most practiced pro could feel this; even if he/she could, ball-to-ball variation is considerably greater than this.

• Finally, suppose we reduced the ball's compression by 10%. This time, the collision is in fact 10% softer. So the compressibility of the ball dominates the feel of the collision.

Actually, the domination is even more marked than the above numbers suggest, because steel is more than 100 times stiffer than a golf ball.

One of the claims made for graphite inserts or real wooden woods is a better "feel". Actually, there may be something to this one, since both materials are more compressible than either steel or copper. However, they're still so much stiffer than the ball that the difference is still pretty minimal, compared to what can be obtained just by changing ball compression.

Let's look at one last rationale for going to wood or graphite to improve feel. A study has concluded that sound is a major component of what golfers call "feel". This study used earplugs with various sound "shapers", from a low-pass filter (gets the high frequencies out) to complete blockers. A couple of interesting results are:

• Clubs tested with low-pass earplugs had a softer feel than clubs tested without earplugs.
• With complete sound-blocking earplugs, the golfers were unable to distinguish consistently the feel of the various clubs.

Distance

This is mostly an argument based on face hardness. Here's a link for more on why that is not really an issue.

Weight

If you're a fan of lighter-than-standard weight or peripheral weighting, then graphite and titanium may hold some exciting appeal for you. Both these materials are lighter for a given volume than steel, so they offer the possibility of lighter overall clubheads, or at least lighter inserts.

First consider clubface inserts. Remember that inserts are in the center of the clubhead, so weight taken out of the ball-striking surface can be moved to the periphery for greater forgiving properties. The other "magic" properties attributes to them (softer for better feel, harder for more distance) are mostly hype.

The whole clubhead can be made of graphite or titanium. We see quite a bit of this now in "wood" clubheads. There is the opportunity to make performance improvements with the lighter material:

• Overall lighter clubhead, for lower swingweight or longer clubs. This should give more distance. There are now oversize driver heads on the market with weights as low as 195 grams, and even lower is feasible with titanium.
• Bigger clubhead, for more forgiveness. This seems to be where everyone is putting their titanium, and some are putting their graphite.
• Thicker cross sections, for a stronger clubhead. This is where some of the titanium is going.

While we're on the subject of strength, there are two very different manufacturing techniques for graphite clubheads: compression molding and injection molding.

• Compression molding involves "laying up" relatively long graphite fibers in a mold, oriented to best resist the forces the clubhead will endure, then saturating the fibers with epoxy resin under compression.

• Injection molding involves squirting a mixture of chopped graphite fibers and epoxy resin into a mold, almost like casting.

It should come as no surprise that compression molding:

• Is more expensive.
• Results in more expensive clubheads.
• Results in stronger clubheads.

Maintenance

There are several maintenance issues that separate the clubhead materials.

The most obvious of these is rust. The carbon steel of a forged head needs to be chrome plated to prevent the head from being destroyed by rust. Scratches in the chrome show oxidation fairly quickly. The other materials (stainless steel, graphite, and titanium) are quite inert and don't rust.

Wood and graphite scratch and abrade more easily than titanium or steel. Wood is pretty straightforward to maintain, for anyone who got through high school woodworking shop, but graphite is more specialized.

Of the stainless steels, 18-8 and 304 are the softest (most "scratchable"), and 17-4 the hardest (most scratch-resistant).

I have never tried to refinish a metalwood head, but that's only cosmetic anyway. I'm less concerned about the club's looks than its playability or integrity. But for those who do worry about cosmetic issues, metalwood refinishing kits are available.

Adjustability

What happens when you need to adjust the loft or lie of the club? I have no knowledge of titanium in this regard. But if you're thinking of adjusting a graphite or wooden head, stop thinking about it.

As for the various kinds of steel:

• Carbon steel (as used in forged irons) is very bendable.
• 18-8 and 304 stainless steel (used in a small and decreasing number of cast iron heads) is similarly bendable.
• 431 stainless steel (the most common material for casting iron heads) can be bent a limited amount. The usual rule of thumb is no more than 2 degrees of bend.
• 17-4 stainless steel (used in almost all metalwoods and a few iron heads) shouldn't be bent without "special equipment", according to the 1995 Golfsmith catalog. (I have been successful myself on one occasion at bending a 17-4 clubhead 2.5 degrees. I have also seen broken 17-4 clubheads after an attempted bend of only 1 degree.)
• 15-5 stainless steel I have only seen in metalwood heads, and have never heard of its being successfully bent.

The reason for this is the hardness of the material. The less sure you are of your loft/lie, the higher on this list you want to be. By the same token, harder clubheads will not nick as easily and will probably last longer; if you ARE sure of your loft/lie, move toward the bottom of this list for a club that will look better longer.