Understanding Putters: Inserts, Grooves, Face Milling, and Roll

December 10, 2012

A lot has been made recently about the importance of “good roll.” Desperate to infuse technology into a club that is usually too simple to get too techy, golf companies sell “good roll” or “hole-seeking spin.” The promote technology that, they say, improves a golfer’s ability to putt a ball and have it hold its line.

While grooves can provide some benefits, they do not necessarily provide the type of benefits that a big company marketing department might try to sell you. The same benefits of a “grooved” style putter can be had with other equipment tweaks that, if you know them, can help expand your universe of putter options, assuming you were liking the way you putted with a grooved putter.

LG and I are big fans of Dr. Bob Rotella. Ask Dr. Bob about hole-hunting spin, and you’ll get a response that measures it as something along the lines of a Paul Bunyan tale. Ask the golf companies–and even some well-known pros–and you might get a different reaction, one full of buy-in. The truth, I’m afraid, is somewhere in the middle.

Golfers have been taking high speed video of putting for years. The purpose of this is to understand how the ball comes off the face of the putter. A ball that starts rolling earlier has a better chance of staying on line. This is physics.

OK, for those who want to tune out of the math discussion, now is the time

Have you ever noticed that it is extremely difficult to sit on a bicycle without moving? However, when you ride a bike, it’s much much easier to stay on the bike if you are already moving.

This is because of a gyroscopic effect produced by the rotation of the bicycle wheels. The wheels maintain their angular momentum unless acted upon by an outside force. However, when the wheels aren’t in motion, there’s no angular momentum, so they fall much more easily. See below

For a physics explanation, see

It works the same way with a golf ball. The angular momentum created by starting a golf ball rolling earlier will keep it rolling unless acted upon by an outside force. If the ball starts by skidding, there is no angular momentum until the ball contacts the ground and starts to rotate.

OK, done for those skipping

So there is some merit to the idea that a golf ball that starts rotating sooner will hold its line. However, a golf ball that starts rolling sooner also will go further because it doesn’t lose as much energy turning a skidding motion into rolling. As such, when you hear about players hitting the ball further with better roll, it’s because they’re used to losing energy, so they instinctively swing harder than needed.

OEM putter makers who make putters with grooves will have you believe that a grooved putter will help you create this overspin. Just like grooves on an iron create backspin, the theory goes that the upward motion of the putter head at impact will allow the grooves to bite into the ball and cause it to spin forward.

This is hogwash, for a number of reasons.

First, a putter is not traveling fast enough in 99.99% of situations for the grooves to actually impact the ball. With iron shots, there is at least mild compression of the surface of the golf ball (and sometimes more than that) that causes the ball to spin. In most cases, large amounts of spin can be produced without grooves, at least in the fairway. Multiple tests have shown that an iron without grooves struck purely on a golf ball will have the same spin profile as an iron with grooves struck purely if the contact is efficient (i.e., from the fairway). Grooves on an iron help when there is a potential of inefficient contact, such as out of the rough, in giving a chance for the uneven surface of the face to make some contact with the ball. With putting, the club is not moving 60+ mph…it’s moving on the order of 10 mph. There is almost no compression of the golf ball, even on really, really long putts.

The second issue is that, for spin to occur, there must be some mismatch between the impact direction and the ball flight. With a wedge, it’s easy to see the ball pop out spinning because the club is moving in one direction and the ball must roll up the face by simple physics. There is no such effect on the golf ball with a putter. The only way to impart upward glancing blows on a golf ball with a putter is to perform an unnatural motion that requires some pretty faulty mechanics and lifting the putter up in the air at impact.

As such, regardless of the marketing, grooves on a putter DO NOT IMPACT THE ROLL.

So what does?

Dynamic loft–in other words, loft at the point of impact. It only makes sense that a putter with lower loft will cause the ball to jump up in the air less than a putter with higher loft. The sooner a ball contacts the ground, the sooner the ground starts to put friction on it and cause it to rotate. The only thing that causes a golf ball to roll forward is its friction with the ground.

Don’t believe me? Watch:

Here’s the rub–a typical off-the-shelf putter will have between 3 and 5 degrees of loft. Many grooved putter will have less than 2 degrees of static loft. So, for a player using the exact same stroke, the dynamic loft (loft at impact) will be lower, regardless of that player’s stroke. I dare say that if a player with a typical putter (e.g., a Scotty Cameron, which are typically 4 degrees) reduced the loft to 1 degree, he/she would see similar playing characteristics to most grooved putters. In other words, it’s not the grooves that promote good roll; it is just that the dynamic loft is lower.

So if grooves don’t actually help putting, what do they do? What are inserts for anyway?

In many cases, grooves, like inserts, can change the feel of a putter or make it possible to have a putter that feels a certain way made out of less costly materials. A Scotty Cameron milled putter is made of 303 stainless steel, milled on a precision CNC machine, the same as an engine block or an aircraft part. An Odyssey insert putter is made of cast 17-4 stainless steel (cheaper metal, cheaper processing), finished by rough bead blasting (cheap process), with a layer of plastic poured in the face, and maybe a quick mill pass on the face to make sure it’s all flat. This process is much cheaper, but it leads to a soft and responsive feeling putter. The end result, a player can get a much less expensive putter (Cameron is typically over $300, Odyssey is typically under $150) that is every bit professional quality equipment.

A lot of press has been put out there for deep milling the face of the putter. Particularly with the newest release of Scotty Cameron putters (see below), deep (or aggressive) milling on the face of the putter has become more popular as many people believe that it makes the putter feel softer.

Both grooves and deep milling alter the contact of the ball and the putter face. Effectively, grooves and deep milling give the ball fewer places to make contact with the face of the putter. Natural frequencies cannot be transmitted as efficiently through the putter head, up the shaft, and into the grip, so the feel changes a bit. Additionally, because the contact is smaller and more localized, there is less of a “ringing” effect, so the amplitude (or strength) of the sound emitting from the putter head is much lower. As a result, there is less vibrations, which makes the putter feel and sound muted. To many players, that is a “soft” feeling that helps them determine whether they made good impact. While this is generally personal preference, it is by and large desirable to have a “soft feeling” putter face to help understand where the impact was made.

So while grooves, inserts, and deep milling do not affect roll, they do affect putting. Your confidence depends at least in part on your making consistent impact, but it is also true that your making consistent impact depends at least in part on your confidence. Grooves, deep milling, and inserts can increase the chances that you will feel that “soft, pure” feeling of a good shot off the face of the putter, giving you confidence that you performed the shot correctly. So there is some good there. But to truly improve your roll, grooves, deep milling, and inserts will not help.

One side note before the finish: although these items do not help roll, position of the center of gravity within the putter head DOES affect roll. Direct placement of the COG on the impact point can greatly increase the efficiency of contact and lead to a lower flight off the face–in other words, the misalignment of the COG and the impact point can cause the ball to fly up in the air, while an aligned COG and impact point would obviate this reaction. However, almost all putters do not position the COG high on the face, and, thus, it is nearly impossible to find a model that does this. One such model is the MACHINE “prize” putter by Dave Billings, but there are not many of these around (see below).

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