Putter Technology

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• Main Menu
• Putter Design Evolution
• Moment of Inertia and Center of Gravity
• Sole Design and Lie Angle
• Putter Balance and Weight
• Putter Grip
• Putter Shape and Face Treatment
• Putter Shaft Location and Offset
• Putter Styles
• Rules Governing Putters
• Impact: Ball Launch
• Face Angle at Impact
• Face Loft and Horizontal Head Path
• Forward Press Effect On Impact
• ASSESSMENT

Moment of Inertia and Center of Gravity

Moment of Inertia:

Because we are not all capable of making contact with the ball at the exact center of percussion (sweet spot) of the face of a putter, it is important to design the putter to reduce the effect, both in direction and ball speed, of a miss-hit.

To do this most effectively, one needs to increase the moment of inertia of the putter. What is moment of inertia, or MOI?

MOI is the measure of the resistance to (angular acceleration) sudden twisting. A simple way to demonstrate it is as follows. Take two 20-pound weights and hold each of them close to your chest. Now try to twist quickly back and forth around your spine. This should be relatively easy to do.

Now, extend your arms out sideways with the weights in your hands, keeping your arms and shoulders stiff. Now try to twist back and forth around your spine quickly. You will find it more difficult to do, because the weights are extended outward away from your spine. What you have done is increase the MOI of the system (your body with extended arms) about your spine axis.

When we talk about MOI, generally the discussion involves iron and wood club design. However, a high MOI is probably as important or and more desirable in putters than the other clubs.

For instance, if you make contact away from the center of the putter face, you want it to resist twisting about the axis which runs vertically through the head, during impact. To do this one needs to have a putter with the weight distributed to the heel and toe of the head thus increasing the putter’s MOI about the vertical axis. The result is a larger area of forgiveness across the face. Today, this one attribute describes the toe-heel-weighted putter, a style created by the Ping Anser many years ago. However, there is a second axis to consider, one that makes the putter forgiving up and down the face. To get this forgiveness, one must increase the MOI about an axis which goes through the putter head from toe to heel but behind the face. To do this one needs to increase the size of the head backward, and weight is added to the back section of the head as far away from the face as possible. This would be a mallet style putter, such as the Frankly Frog, with the center of gravity far back from the face. This allows for a high MOI about the vertical axis (forgiveness from toe to heel) and a high MOI about the toe heel axis (behind the face) maximizing forgiveness up and down on the face. The bonus in this case is ease of making the putter face balanced and with the Split Weights it is a little more stable because of a high MOI about the third axis from the face to the back. The Frankly Frog Putter is one of the most stable, well balanced and forgiving instruments available.

Center of Gravity:

As mentioned in the discussion about MOI, we need to move the center of gravity (c.g.) back and distribute the weight away from the c.g. to make it more forgiving. But as we will see, we also need to keep the c.g. as low in the head as possible.

When the player places the putter behind the ball resting on the ground, the contact point with the center of the ball on the face is 0.84 inches above the sole. However, during a stroke, the putter head is raised above the green surface by up to 0.25 of an inch. Raising the club by this much will lower the impact point on its face to about 0.60 inches above the sole. If during the stroke the putter is raised more than 0.25 of an inch, then the contact point on the face is lowered even more.

Most blade-like putters have a c.g. location about 0.65 inches above the sole, which means that contact will be made with the ball on, or below the c.g. of the head in normal putting conditions. Because of the low MOI (about the toe - heel axis) of the Anser -style putter, the forgiveness of a miss-hit up and down the face is not very good. The result of this kind of miss-hit is a real drop in distance for the same head speed. This type of stroke happens readily when putting the ball which is resting against the fringe of the green.

A lower c.g. well back from the face, coupled with a large MOI about the toe - heel axis, will assure more efficient impact with the ball and thus more consistent distance control.