MOI and Putter Design

MOI.  It’s been a buzzword in putters for years.  MOI stands for Moment of Inertia.  We won’t bore you with the details of how it’s calculated (there are plenty of places to find that on the net), but suffice it to say that MOI is a measure of how stable and forgiving a putter is.  The higher the MOI of a putter head, the less it will twist on an off-center strike and the more energy it will transfer to the ball.  

The animation below visually shows how a high MOI putter is more forgiving on an off-center, toe mis-hit than a low MOI putter.  At impact, the low MOI putter twists open.  Some of the energy that should have been transferred to the ball to get it to the hole is instead converted to rotational energy of the putter head.  As a result, the putt comes up short and pushed to the right.  A high MOI putter twists less and transfers more of its kinetic energy to the ball, keeping it closer to its intended line and speed.

Importantly, MOI is essentially the only objective and quantifiable metric we have in the putter industry.  There are tons of gimmicks and claims out there about various aspects of putter designs.  “These (insert gimmick here — grooves / alignment lines / color scheme / whatever) — help you sink more putts!”  But none of those claims can ever really be quantified, nor can one gimmick claim to be objectively better than another.  But MOI can be measured and quantified and used as a point of comparison.  Take two virtually identical putters with the same dimensions and weight, with the same general look and feel - if one of them has a substantially higher MOI, that putter is better, period.  It will twist less on off-center strikes, transfer more of the energy of the stroke to a ball on a mis-hit, and be more “forgiving” in general. 

Designing for MOI 

Increasing the MOI of a putter requires having more weight further from the putter’s center of gravity.  That can be accomplished in 4 ways:

  • Making the putter bigger
  • Making the putter heavier
  • Changing the shape to redistribute mass away from the center of the putter
  • Using lighter materials near the center of the putter and heavier materials away from the center

Picture in your mind’s eye the biggest, ugliest, super-MOI putter you’ve ever seen — what many would teasingly refer to as a “frying pan on a stick”.  That putter likely embodies several of these MOI-improving design techniques.  It probably has a huge footprint with weights sticking way off the corners, and it may have holes in the middle or be made of plastic instead of metal.  It may also be a lot heavier than a normal putter.  While this putter has a higher MOI than a traditional blade, it definitely looks and feels different.  While putters like this have become increasingly popular due to their high MOI and added forgiveness, many golfers dislike the look and feel of these putters so much that they simply won’t play them.

Our objective: to use 3D printing technology to create normal and traditionally shaped and sized putters with greater MOI.

How do we do that?  First, let’s take a deep dive into an example of how putter design affects MOI.

Let's start with a basic blade made of steel, 4.5” wide x 1” tall (which is average for a heel-toe weighted blade), and 0.4” deep (just thicker than a shaft).  Such a putter would look like this:


This putter would weigh 231.6g.  With a target weight of 350g (normal for modern putters), that leaves us 118.4g of additional weight to add to the putter and place strategically.  Let’s say we add 118.4g of tungsten to this putter right behind the center of the face (we'll give it a blue color to make it easy to see), and let’s cap the total depth of this putter at 1” (a pretty normal blade putter size).  118.4g of tungsten at 1” tall and 0.6” deep would be 0.662” wide.  If we position that block of tungsten right in the center of the blade, our putter would look like this, and have a total MOI of 2710:


Now let’s say we decided to chop that block of tungsten in half and start stretching it out toward the toe and heel, as shown in the animation below.  As you can see in the chart on the right, the further we space out the tungsten weights the higher the MOI of the putter.  In fact, the growth in MOI is exponential in relation to the width of the weights.  So to maximize MOI it’s critical to move weight as far out to the toe and heel as possible.

It is this fundamental concept that has driven the design approach to our 3D printed models.  Unlike many putter designers seeking higher MOI, we have not made these putters bigger or heavier.  We have intentionally kept them within the range of “normal” putters for size, shape, and weight.  Instead we have sought to use the new capabilities of 3D printing and a multi-material construction approach to increase MOI.

Our “Closer” model has exposed tungsten weights and is a great visual example of how we have applied this concept.  Other putter manufacturers sometimes include 10 or even 20 gram weights in the soles of their putters.  While that’s better than placing that weight in the center of the putter, it really doesn’t have a big impact on MOI.  Those weights need to be stretched all the way out to the ends of the putter, and be much heavier to really improve MOI.  Our “Closer” model has a massive 150g of tungsten in it, and because 3D printing allows us to make shapes that milling cannot, we’ve stretched those weights all the way out to the toe and heel.   As a result, the MOI of this putter is north of 6000!  There are no other “normal” size and weight blade putters on the market that are anywhere near that level of MOI.  

This is innovation -- using new technology to make a better product.

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