RockBats Technologies

Slope-of-Grain

For 100 years, bat manufacturers typically graded the wood quality in their bats by addressing the straightness of the EDGE grain ONLY. This straightness of the wood grain is referred to as “slope-of-grain” - zero slope is the strongest wood. There are (2) slope-of-grain measurements on a wood bat – on the EDGE grain and on the FLAT grain. EDGE-grain slope-of-grain is easiest to measure because these are simply the growth rings of the tree. FLAT-grain slope-of-grain is more difficult to detect with the naked eye. Wood is weakest across the FLAT grain, and high slope-of-grain on the FLAT grain is the weakest and most critical situation that results in 2-piece broken bats.

Not grading the FLAT-grain slope-of-grain of Ash blanks was not a problem in past years, because Ash logs were typically split during the manufacturing process to produce bat blanks. When blanks are produced by splitting the log, this results in the straightest grain along the bat. In modern times, logs are often sawn, and this may result in baseball bat blanks that may not have perfectly straight-grain wood along their length – especially on the FLAT grain face.

The 2 most important details to understand is that there was no industry standard as to what level of slope-of-grain should be followed for wood baseball bats, and that slope-of-grain on the FLAT-grain face was left unnoticed, ungraded, and not well understood. As more and more bat manufacturers began to produce maple bats, most of which were being produced from sawn bat blanks – this evolved into the “broken bat problem” that became well known in the wood baseball bat industry.

In 2002, RockBats developed a slope-of-grain grading methodology that significantly reduces dangerous slope-of-grain bat failures. Bats that have straight-grain less than approximately 2 degrees will maintain approximately 90% of the strength of a wood bat having perfectly-split straight-grain wood. If a wood bat with this level of straight-grain breaks due to a bad mis-hit by the baseball, it will typically rupture or splinter. On the other hand, if a wood bat has slope-of-grain that exceeds approximately 3-degrees on both the EDGE and FLAT grain, it will have less than 70% of the strength of a bat with perfectly split straight-grain wood. It was not uncommon to find bats with 10-degrees slope-of-grain, which have less than half the strength of a straight-grain wood bat. Bats with a higher degree of slope-of-grain are more likely to break into the dangerous 2-piece breaks.

For the first time in 100 years, there was now a measurable wood property that could be followed by bat manufacturers to assure wood strength for baseball bats – that property is called “slope-of-grain”. For the 2009 season, Major League Baseball adopted a slope-of-grain grading criteria that all bat manufacturers were required to follow. Pro Quality slope-of-grain is now established as a 1:20 slope-of-grain on both the EDGE- and FLAT-grain faces of the wood.

To assist in the better visualization of the slope-of-grain on the FLAT-grain face, the idea of using an ink spot on the handle of maple (and birch) bats was developed. The idea of using an ink spot on wood was developed in the 1960’s in Forest Service research involving the measurement of slope-of-grain on wood veneer sheets for plywood. The idea of using this ink spot technology on the handle of baseball bats was first mentioned in the 2006 RockBats Tech Note C. Be sure to visit our Tech Notes page to read more on this subject.

Flat-grain contact for maple bats - FORCE Technology®

When technologies are followed for 100 years, they become a rule-of-thumb. This was the case for the rule-of-thumb of hitting with the LOGO UP with wood bats. Because Ash bats have been the primary wood species used for the past 100 years, the rule-of-thumb for hitting with an Ash bat was to hit LOGO UP so that contact with the ball would occur on the EDGE grain. The reason this was the recommended orientation was because repeated contact on the FLAT-grain face would result in annual ring separation (called “flaking”) in an Ash bat.

When maple bats entered the industry in the 1990’s, manufacturers who produced maple bats continued with the same rule-of-thumb – apply the logo on the FLAT-grain face so that ball contact is made with the EDGE grain.

Long story short, RockBats was the first to determine and recommend that FLAT-grain contact is the stronger and preferred orientation for maple bats – in 2005. This meant applying our logo on the EDGE grain so that the same LOGO UP rule still applied. As you might expect, given that there was a 100-year-old rule-of-thumb, it was a difficult uphill climb to convince players (and the industry) that this was the stronger and preferred orientation.

Starting in the 2009 season, the major leagues adopted a FLAT-grain contact requirement for maple (and birch) bats in the bat supplier regulations. All manufacturers that supply maple (and birch) bats to the major leagues were required to orient their bats for flat-grain contact. Be sure to read our story in the About RockBats to see more details on how we developed this.

Sweet-spot Testing and Identification

Every RockBat model is tested to identify the location of the sweet spot on the barrel of the bat. This location is marked with our GOLD DIAMOND vinyl stickers.

RockBats is the ONLY bat manufacturer that tests and identifies the Sweet Spot.

Our sweet spot mark is a great training aid as well as a teaching tool for players of all ages. Coaches/parents can instruct young players on where to setup in the batter's box; to put the sweet spot over the plate. Advanced players can track where they are making contact on the barrel, and determine if they need to adjust their location in the batter's box; or perhaps consider a longer or shorter bat.

How do I orient my RockBat to hit on the sweet spot?

RockBats are designed to be hit LOGO UP, which results in FLAT-grain contact. Our sweet spot diamonds are placed on the same edge-grain face as our RockBats logo, so when you make ball contact the ball mark should be on the front side of the barrel, 90-degrees around the barrel, from where your sweet spot is located. The photo below shows correct ball contact for a left-handed swing. A right-handed batter would make contact on the opposite face.

The importance of hitting on the Sweet Spot

Most ballplayers know that hitting the baseball on the sweet spot results in the least vibration in the hands, and in the fastest ball velocity off the barrel. However, what is also important to understand is that hitting AWAY from the sweet spot causes the largest stress in the handle. Even a bat with perfect straight-grain wood might break if mis-hit significantly away from the sweet spot.

Note that both inside and outside pitches that are approximately 5-inches away from the sweet spot will both cause significant stresses in the handle of the bat. On the other hand, ball contact directly on the sweet spot results in the lowest vibration and the least stress in the handle.

It is important to understand that wood bats may break due to mis-hits away from the sweet spot - even when there is perfect straight-grain wood. HOW a bat breaks (i.e. failure mode) that tells us if a wood bat had superior-quality straight-grain wood, or inferior-quality slope-of-grain wood.

Our RockBat Tech Note – "Failure Stresses and Failure Modes of Solid-Wood Bats" – discusses this phenomenon, and also explains more about failure modes in wood.

The 3 videos below show ball contact at an inside pitch, an outside pitch, and at the sweet spot.

Inside Stress Outside Stress Sweet Stress