What’s In a Bat? Inside The Process of Bat Manufacturing.

Ever wonder how and where the famous Louisville Slugger baseball bats get made? (via Scott Heath)

A tour of the Louisville Slugger Museum & Factory gives visitors a sawdust-covered glimpse at the manufacturing process behind the world’s most iconic baseball bat. Here’s a condensed version: the factory receives stacks upon stacks of cylindrical wood billets; the billets are shaped into baseball bats; the Louisville Slugger insignia is branded onto the bat; the bats are then finished with a player’s choice of coating.

Much like the story of Pete Browning initiating a booming baseball bat business, some of the details of the tour are a bit fuzzy. But regardless of the details of how the Louisville Slugger, the player, came to use a Louisville Slugger, the baseball bat, we attribute Andrew “Bud” Hillerich with the realization that the tools and techniques of his family’s woodworking business could be applied to baseball. However, the modern baseball bats of today are a far cry from the PB1 model bat, as Louisville Slugger and its competitors have applied new technologies and processes from other industries to bat manufacturing.

As simple as wooden bat-making appears, there have been many changes in the process over the years. There are still people who hand carve bats, but more often than not, companies are trading in their calipers for computer aided design and computer numerical controlled (CNC) automated lathes. The most commonly discussed change has been the shift from hickory to ash to maple as the primary wood of choice. This goes far beyond the simple selection of a type of tree; when you look at the wooden bat-making process as a whole, there is still much more room for innovation. Let’s walk through the manufacturing process as it stands now, and consider some changes that could be made in the future.

First, we’ll check in with Major League Baseball to make sure we’re making bats that meet league regulations. Baseball is a game of codified rules, so of course, there are rules about the bat. Specifically, we’ll look to Rule 1.10:

(a) The bat shall be a smooth, round stick not more than 2.61 inches in diameter at the thickest part and not more than 42 inches in length. The bat shall be one piece of solid wood.

(b) Cupped Bats. An indentation in the end of the bat up to one inch in depth is
permitted and may be no wider than two inches and no less than one inch in
diameter. The indentation must be free of right angles and may not contain any
foreign substance.

(c) The bat handle, for not more than 18 inches from its end, may be covered or treated with any material or substance to improve the grip. Any such material or substance that extends past the 18-inch limitation shall cause the bat to be removed from the game.

For now, our focus is on “The bat shall be one piece of solid wood” and “The bat handle, for not more than 18 inches from its end, may be covered or treated with any material or substance to improve the grip.” We’re all familiar with the rule regarding solid wood-no corked bats, no metal bats, no composite materials—and we all know there can’t be any pine tar on the taper or barrel of the bat. But beyond those specifications, there don’t seem to be many limitations regarding the manner by which the bat is manufactured.

Along with the rules about bats, there are rules about who can make bats. While major league players are able to select a bat of their choosing, bats must be approved by MLB:

Major League Baseball requires prospective bat providers share every detail of their manufacturing process, from how they cut to what tool they use to do it. Suppliers are scrutinized, and prospective owners quizzed on their knowledge of the gritty details.”

In addition to sharing details of the bat’s production, bat manufacturers also must pay an annual administration fee and an insurance policy. These annual costs were estimated to be as high as $65,000 annually in 2003. Today, an entrepreneur can peddle wares to major league players after about $30,000 annually in fees and insurance premiums, or pitch a new bat design to an established manufacturer. Given the potential to build a multi-million dollar company based on the sales to both professional and amateur players, it’s not surprising that more woodworking professionals are applying their craft to wood bats.

Although the approval process isn’t cheap or trivial, for the 2018 season, 35 companies are authorized to manufacture wood bats for in-game, major league use. These include Louisville Slugger, but also BWP Bats, Mizuno, Marucci, Victus, Warstic, Homewood Bats, Sam Bats, Chandler Bats, and Dove Tail Bats, among many others. Generally speaking, they all follow the same steps, beginning with sourcing wood.

Obviously, to make a bat out of a solid piece of wood, we need to start by looking at trees. We all know that bats were once made of hickory, and were much heavier. And we know that ash bats gradually supplanted hickory. While players were using maple bats throughout the 1990s, Barry Bonds is often credited with the surge in maple’s popularity. Ash and maple have grown exceptionally well in northwestern Pennsylvania and southern New York; many bat manufacturers source their materials from this area. Today, about 75 to 80 percent of MLB players swing a maple bat, while 10 percent are still swinging ash, and about 10 to 15 percent use birch. There are good reasons to choose a denser wood like maple over ash: maple is harder than ash and maple bats don’t tend to flake the way ash bats do. Plus, a maple bat is much more durable. But, as we’ve seen in games, when a maple bat breaks, it can shatter into multiple jagged fragments, posing an injury hazard to players, umpires, and fans alike.

In 2008, MLB formed a committee, with the guidance of the MLB Safety and Health Advisory Committee and the Player’s Association, to revisit the Wooden Baseball Bat Specifications. MLB enlisted the help of the University of Massachusetts Lowell Baseball Research Center (UMLBRC), and U.S. Forest Service’s Forest Products Laboratory researcher David Kretschmann. Their research examined the patterns by which a bat breaks, and conducted a search for wood species that are suitable for use in wood bats. The search for new lumber isn’t driven just by safety concerns. It was also in response to environmental changes affecting both the availability and quality of trees.

The Worcester Red Sox and the Problem of History
As the Red Sox prepare to move an affiliate, Pawtucket stands to lose more than just baseball.

As has been widely reported, the emerald ash borer is decimating the supply of ash in Pennsylvania. And the effects of climate change don’t stop with the development of a more hospitable environment for these invasive pests; as the temperature and growing season changes, the growth pattern of trees is also changing. Forestry researchers hypothesize that although increasing temperatures encourage faster growth, rapid growth also means that trees are weaker. Of the four species the researchers tested, all four have lost eight to 12 percent of their density since 1900. Additionally, increased use of fertilizer is known to lower wood density. While these particular studies don’t include ash or maple trees, it’s not unreasonable to consider that North American forests have undergone the same changes. Even if the emerald ash borer were to be eradicated, there’s a very good chance the ash of today is not the same as the ash of 50 years ago.

If we were to start from scratch and look for a new type of wood, what would we look for? Ideally, the wood used in bat construction would be hard and durable, like maple, but strong and lightweight, like ash. If the goal is to achieve a bat that is less prone to shattering, especially into multiple fragments the way maple does, we’d also look for a wood with a long slope of grain. A tree’s slope of grain is a reference to the orientation of the axis of the wood (in this case, the bat’s length) to the angle of the fibers of the wood; it’s a function of the tree’s growth. Ash has a much more distinct, long slope of grain, whereas maple’s diffuse, porous structure leads to a less defined, meandering slope of grain. Companies use the ink dot method to visualize the slope of grain—sometimes you will see a small circle on the taper of a bat, which is where this technique is used. But we have more sophisticated ways of measuring the slope of grain.

Slope of grain isn’t the end of the discussion, though. Wood density is also important. Even within maple, though, there is a distinction to be made: higher density woods are less fragile than low density maple. So when looking for new sources of wood, researchers compare new, alternative woods to ash as their standard, looking for wood that is dense, with a long slope of grain.

The UMLBRC studies everything from patterns of wood baseball bat breakage to the durability of wood bats based on wood species; their laboratory has worked with MLB to determine the regulations and inspection processes for MLB approved wood bats. Of particular interest is the testing methodology used to examine the durability of different wood species. This 2012 paper compares yellow birch to white ash, with white ash being selected as the benchmark. Although this particular paper is limited to testing yellow birch, it establishes a test for alternate wood species. More recently, UMLBRC evaluated bat dimensions and profiles in conjunction with wood of various densities, and concluded that “profiles with low volume, large diameters at 30.5 and 38.1 centimeters (12 and 15 inches) as measured from the base of the knob, and composed of high-density wood exhibit the best durability during gameplay”. This durability criterion can be used to evaluate new wood bats as part of the MLB approval process.

While the search for new sources of wood is ongoing, there are other factors to consider. Even after wood has been sourced and selected, the method used to cut it can vary. Traditionally, billets are cut from logs using a split-and-turn method, which splits logs into wedges called bolts, and are in turn cut into billets. Hillerich & Bradsby’s lumber supplier uses a laser guided boring machine to cut billets, which allows  more high quality billets from a piece of lumber. A single tree can produce enough wood billets to produce 60 completed baseball bats. We can use newer imaging technology to locate areas of higher density and longer slope of grain, to maximize the output of quality billets.

The billets are then dried—and here we have another process which isn’t as cut and dry as it sounds. Traditionally, billets are dried in a kiln for several weeks, until they reach 10 to 12 percent moisture content. The initial moisture content varies between different types of wood; maple tends to have a higher moisture content than ash, which leads manufacturers to kiln dry maple longer than ash. However, you don’t want to overdry wood, or it will become too brittle.

On the other end of the spectrum, sometimes there is still residual moisture at the center of the billet if it isn’t dried sufficiently. Thus, it’s no surprise that Hillerich & Bradsby and Sam Bats improved upon the drying process by introducing vacuum drying, which allows the drying process to take days rather than weeks, in addition to providing more consistent, even drying throughout the wood. Although it’s not as hot as a traditional kiln, vacuum drying uses low pressure in combination with an elevated temperature, so there is still the potential for heat damage. A freeze drying process can also be used to dry lumber, which can mitigate the potential for heat to destroy the wood.

Once the bats are cut and sanded, the bats are finished with a player’s choice of coating, ranging from an opaque black, allegedly a special request from Ken Griffey Jr., to a clear coat, which highlights the natural beauty of the wood’s grain. Finishes provide aesthetic appeal, but they also add to the hardness of the bat. After a varnish is applied, bat manufacturers can treat the finished bats with a compression device. These rolling devices not only polish the bat to a sheen, but by delivering 500 pounds of pressure to the entirety of the bat’s hitting surface, the device compresses the softer grain of the wood to achieve a more consistent, harder hitting surface.

This is the automated version of bat boning, although even after the bat leaves the factory, players sometimes take this compression step into their own hands. Because ash is less dense than maple, bat boning has a greater impact on ash than on maple. Although much of the “boning” process is automated now, players continue to bone their bats to maintain their surface.

Now that we’ve had an overview of wood bat manufacturing, we can see some areas where baseball might improve upon the existing processes. First, let’s take a look at Rule 1.10 again: “The bat shall be one piece of solid wood”. There are really no limitations regarding the treatment of this one solid piece of wood. And Rule 1.10(c) is directed only toward materials and substances to improve the grip. This doesn’t prohibit us from adding additional materials to the barrel of the bat; indeed, anyone watching a game can see laminated branding, and the wide variety of lacquers and finishes covering the barrel of a bat. So in general, there don’t seem to be many limitations regarding the manner in which the bat is manufactured. What if, instead of just looking at alternate sources of wood, we improved on the wood that is available?

Although wood is a solid, it’s also a porous, heterogeneous material. The cell walls of wood primarily comprise 55 to 75 percent cellulose and hemicellulose, and 15 to 30 percent lignin. The composition of wood, both in terms of its cellular structure and porosity, means that wood will absorb ambient moisture. This is why some players store their bats in a humidor, where they can provide a more controlled climate. We know the humidity and moisture content of bats factors into bat performance: in tests of wood bat moisture contents, UMLBRC found that after soaking wood bats in humidified air to achieve an increase in the moisture content from 6.7 to 10.9 percent resulted in a one percent increase in batted ball performance. What if we could use some kind of treatment or curing process to prevent these changes in moisture content?

You’ve probably participated in some of these treatments yourself, if you’ve ever oiled a wooden cutting board or stained furniture. These liquids take advantage of the porous nature of wood, seeping in and penetrating the surface. For example, one of the functions of oiling a wooden cutting board is to prevent water and moisture from seeping into the cutting board; a moist environment is a haven for microbial growth, and water will eventually rot the wood’s structure. We can use this same line of thought to treat wood bats to maintain their moisture content, as well as provide other advantages.

The chemical treatment of wood to stabilize and improve the properties of wood is a very well known technique. These include polyethylene glycol treatments, which can be used to drive moisture out of wood. There’s also acetylated wood, which can result in durable, stronger wood that also resists water absorption. The acetylation process converts some of the hydroxyl moieties on the lignin, cellulose, and hemi-cellulose of the wood into acetyl moieties. By “capping” the hydroxyl moieties, it’s a little more difficult for water molecules to reside in the wood.

It isn’t entirely clear where one would draw the line between wood and not-wood. Acetylation makes slight changes to the molecular structure of wood, but it still begins with a piece of wood. What if we were to use other treatment processes to chemically densify wood? Chemical treatment of wood, followed by compression, can lead to wood that is dense and strong, yet lightweight, and resistant to moisture. This process also begins with a solid piece of wood, but it most likely wouldn’t resemble the wood bats we know now by the end.

We haven’t even touched on the finishing process; this seems to be an area where there is a lot of room for improvement. Many of these finishing solutions are proprietary; while they provide an improved aesthetic, they also serve a more practical purpose. Many companies contend that these proprietary varnishes and coatings applied in the finishing stage provide extra hardness and durability to a wooden bat. This brings us to another issue: while we must be mindful of the waste byproducts of the lumber itself—converting a five-pound billet to a two-pound bat necessarily means sawdust waste for every single bat produced. We must also bear in mind the waste generated from laminates and varnishes that are used to finish the bats. Looking for improvements in the bat manufacturing process could not only mitigate these environmental concerns, but also provide for a safer wooden bat. We could easily envision moving beyond just a varnish, to sleeves and polymeric coatings to arrive at a safer wooden bat.

As always, baseball is rife with superstition and hesitance in the face of change. It can be particularly hard to sell changes to players if there is no evidence suggesting any particular properties of a wooden bat will provide improvements in performance. However, there’s a clear need for continued development in this area, and ample room for improvement in the manufacturing process, all of which goes far beyond the simple selection of wood. We have a number of tools at our disposal by which we could improve the available raw materials and the durability of the finished wooden bat, while still adhering to Rule 1.10. By ignoring the other steps in the manufacturing process and reducing baseball bats to a “maple or ash?” quandary, we’re missing the forest for the trees.

References and Resources


Stephanie Springer is an organic chemist turned patent examiner. Follow her on Twitter @stephaniekays.

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8 Comments on "What’s In a Bat? Inside The Process of Bat Manufacturing."

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winkdo
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winkdo

Awesome article. I’ve been trying to learn more about bat technology as it has developed over the years. I wonder if any current players will try and break the mold with material or bat preparation as time goes on.

I wonder if there are many international bat companies in Europe or Asia are doing things differently or do they use American companies as their primary bat distributors.

Jetsy Extrano
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Jetsy Extrano

Durability is good, but what’s known about game performance based on bat profile and material? We know COR matters a ton with metal, and that’s part of maple too, right? Is there a wood moisture level maximizing COR? What profile optimizes bat speed and sweet spot size?

But any article with grain slope is a good article right there!

Dennis Bedard
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Dennis Bedard

I got so immersed in this article I was sorry it ended. I hope this one is just a first installment. What about the effect of aluminum on the industry?

Paul22
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Paul22

Maple wasn’t used 50 years ago and bats are better engineered to be lighter and increase bat speed. Also, for whatever reason, not every player can get a bat from the manufacturer of their choice. Louisville bats may be most in demand but they limit their customers to the better players/prospects. Perhaps my information is wrong or outdated but that seems unfair to lesser players if the best made bats are not available to them

hoya33
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hoya33

Use to love the Blue ring Big Stick Adirondack bat in the late 60’s early 70’s so fantastic wood used to make those bats.

hoya33
Member
hoya33

LOL ,In high school, our baseball coach taught woodworking class. We spent most of the time in class talking ash,maple sports but our big assignment was to make baseball bats. We went out and took batting practice with all the bats if the majority of the bats survived batting practice we all received a A if more than half cracked we all got a B. That kept all our players eligible really was a fun class.

Dave P
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Dave P

Have there not been foreign experiments with bats? Sampling different tree types from the Amazon or SE Asia? Some Australian type of wood?
Does Alaska have anything to offer?

Llewdor
Member
Llewdor

I always thought Birch would make a good bat. It is extremely crush resistant – second only to oak, but it’s much lighter than oak.

It’s also significantly heavier than maple, as I recall (though when I did my research I used white birch, not yellow birch).