Bowling ball

Specifications

The USBC and FIQ specifies that bowling balls may only be made from uniform, solid materials with a density less than or equal to 3.80 g/mL. The weight of the ball must not exceed 16.00 pounds (7.26 kg), with no lower bound for weight. The hardness of the ball must be at least 72, as measured by a Type D Shore durometer at room temperature (68-78 degrees Fahrenheit). A ball may have a circumference between 26.704 inches (67.83 cm) and 27.002 inches (68.59 cm), and a diameter in the range of 8.500 inches (21.59 cm) to 8.595 inches (21.83 cm).^[2]

The surface of the ball is required to include markings to indicate the manufacturer's brand name, the name of the ball, the center of gravity (before drilling), the orientation of the core (the Pin), and the axes of the high and/or low radius of gyration (as applicable). Additionally, markings must include an individual serial number and the logo of the USBC.^[2]

Holes are allowed to be drilled into a bowling ball for a variety of reasons, and bowlers must be able to demonstrate that such holes can be used as claimed. Up to five holes may be drilled for the bowler's fingers for one hand, and each finger hole may have a small additional hole that intersects for ventilation. A "balance hole" may be added to alter the mass distribution. The USBC recently changed their rules that affect no-thumb bowlers more than those using a conventional grip. Now any hole not used explicitly for gripping during the approach is to be considered a balance hole and only one balance hole is allowed. This means that no-thumb bowlers would have to take out their thumb hole or their balance hole if they have both. This is because it may give them the advantage of special weighting, which can help give the ball a higher spin rate.^[3] A "mill hole" may also be used for inspection purposes.

Bowling balls are required to be balanced such that after drilling the difference in weight between the left and the right side (around a line bisecting the fingers and thumb) does not exceed 1 oz and the difference between the top and bottom of the ball does not exceed 3 oz. There are special scales designed to weigh/compare different halves of the ball.

The radius of gyration must fall between 2.460 inches (6.25 cm) and 2.800 inches (7.11 cm), and the differential radius of gyration must not exceed 0.060 inches (0.15 cm). The coefficient of friction must not exceed 0.320.^[2]

Materials

Historically, bowling balls were often made from dense hardwoods such as Lignum Vitae, but starting in the early 20th century, hard rubber became the primary material for bowling balls. The first bowling balls to be made from polyester ("plastic") were produced in the late 1950s. This became the predominant material in the 1970s. In the early 1980s, polyurethane ("urethane") bowling balls were introduced. Urethane balls provided greater friction on the lane, which allowed for a greater angle of entry of the ball to the "pocket" (space between two of the front-most bowling pins, known for providing the greatest percentage of strikes), and as a better match to the increasing use of polyurethane varnish on wood lanes (replacing older lacquer varnishes), and with wood lane "overlays" and fully synthetic lanes using a polyurethane surface. This is desirable, as a greater entry angle tends to provide a higher striking percentage.^[4][5][6]

In the early 1990s, a new material known as "reactive resin" was introduced. Reactive resin is still made from polyurethane, but has been treated with additives while in a liquid state that create pores in the coverstock that allow it to absorb oil. As oil is absorbed into the ball rather than sitting on the surface, there is greater friction between the ball and the lane.^[4][5]

In the late 1990s, "particle" balls were introduced. By distributing small particles into the reactive polyurethane cover, manufacturers are able to create even higher friction. This is particularly noticeable on oily surfaces, where a particle ball is able to create considerably more friction than balls of other materials. The types of particles and their properties may vary between balls and manufacturers.^[4][5]

Particle and reactive resin balls are common in modern play, particularly on lanes with relatively higher volumes and/or lengths of oil.^[4][5]

Plastic balls are also commonly thrown when a bowler wants a ball that will move in a very straight line, particularly while trying to make spares. Urethane balls are less common, but may still be used for strike shots on less oily lanes.^[4][5] Urethane balls have also made a comeback with some two-handed professional bowlers like Jesper Svensson and Kyle Troup, who often find reactive balls difficult to control given the high revolution rates they put on their shots.^[7]

House balls lying on ball return.

Grips and finger holes

The way the finger holes are arranged on the ball surface changes how the bowling ball moves down the lane.^[8] The drilling configuration is determined by the positions of the finger holes relative to the markings on the surface of the ball, and may also be positioned relative to the axis of rotation of a particular bowler. The axis is typically identified according to the Positive Axis Point (PAP), which marks the axis before axis migration has begun.^[9]

In the United States, most bowlers only use holes intended for the middle and ring fingers of the dominant hand, as well as the thumb of the same hand. A "conventional" grip is one in which the bowler inserts the thumb fully, and the fingers up to the second knuckle from the tip. A "fingertip" grip is one in which the bowler inserts his fingers only to the first knuckle from the tip. Some variety of fingertip grip is favored among professionals and most amateurs, as this configuration allows most bowlers to impart greater rotational velocity on the ball. Some bowlers, notably Mike Fagan^[10] and Robert Smith,^[11] use the "Sarge Easter Grip," in which the middle finger is drilled to fingertip standards to the first knuckle, while the ring finger is drilled to conventional standards to the second knuckle.

Though fingertip grips traditionally include having the thumb fully inserted, some bowlers, notably Jason Belmonte^[12] and Osku Palermaa,^[13] hold the ball with two hands and do not insert the thumb. This style came into prominence in the 2000s.

It is common for bowlers, particularly those with fingertip style drillings, to place inserts into the holes rather than grip the holes directly. This can be done to vary the texture and shape of each hole to match a bowler's preferences.

Composition

The first bowling balls used in Hunan, China were made of wood. In about 1906 the first hard rubber balls were produced, such as the Brunswick "Mineralite" ball, and these remained the standard until the 1960s and 70s. These decades saw the emergence of plastic (polyester) balls.

In the early 1970s, they began experimenting with the hardness of the plastic balls. The reason for this is to allow the ball to "grab" the lane better. Plastic balls were difficult to hook on tough oil conditions. Until the 1970s, there were no rules regarding the hardness of the bowling ball's surface. PBA member Don McCune took advantage of the non-existence of such a rule. At the time, he worked for Chuck Hamilton, who invented the "soaker"—a plastic (usually polyester) ball he softened "in the garage" with chemical solvents such as MEK, which excrete a sticky substance, allowing the ball to hook more on oily conditions. At times, the balls were soaked to the point that the balls might even end up lopsided. Columbia—a more established manufacturer of bowling balls—came out with a series of "yellow dot" balls that were similar in function to the "soaker". The hardness of the ball's surface came under ABC scrutiny because of the increased scoring, particularly by McCune, who with his "soaker" won six PBA tournaments in 1973 and PBA Player of the Year honors. The ABC established a durometer hardness rule of 72, which barred even some of the out-of-the-factory softer balls. The PBA took the issue even further by applying a more strict 75 hardness rule. To effectively test the hardness, the PBA required each ball to bear a 0.25-inch deep hole, just above the finger holes. The durometer was inserted into the hole, allowing the meter to perform the test beneath the ball's surface.

Sanding of the bowling ball surface was another technique to soften the ball's surface. Once the track area was located on the ball, the bowler sanded it to make the surface more abrasive, allowing the ball to hook more. Bowlers also applied solvents to the surface during tournament play—rubbing the chemicals into the cover using a rag. More rules by the ABC had to be passed, including restrictions from doctoring the bowling ball's surface at any time once the ball has passed inspection by an official.

At some point in ball making and drilling, the ABC introduced ball balance regulations to prevent people from taking advantage of certain forms of "weighting". It was possible to drill the grip at a location relative to the weight block to achieve some effect, such as to help the bowler make it roll earlier or hook more. Guide holes were also used to stabilize the roll of the ball, by drilling the guide hole in perpendicular to the track area of the ball. This allowed the ball to avoid over-hooking or roll-out before hitting the pocket.

In 1981 Ebonite began manufacturing the very first urethane cover stock bowling balls and sold the rights to AMF. Ebonite produced AMF balls at that time. Ebonite did not believe that bowlers would pay the $80.00 price this new technology demanded. That ball became the AMF Angle and this one coverstock change allowed the ball to get a better grip on the urethane finishes used on natural wood lane surfaces, which changed the nature of the bowling game significantly. Then in 1991, Nu-Line Industries produced the X-Calibur, a reactive resin cover. Part-time professional Steve Cooper was the owner and president of the corporation. But production lagged in the early days, allowing firms like Storm, Brunswick and Columbia to enter the reactive market by the following summer. The race to create more and more dynamic balls was on.

Prior to about 1990, the ABC "static" ball balance regulations were adequate. The core was usually a uniform sphere centred inside the ball. Then competition among ball manufacturers motivated the production of balls designed to offer more than the "static balance" tricks. Materials and fabrication changes have since allowed the assembly of balls whose interior components have a much greater range of density, thereby offering a new ball choice that, in physics terms, involves the moment of inertia of a solid sphere. Eventually, "dynamic balance" regulations had to be adopted.

Physics

Weight block basics

For various formulaic purposes, physicists divide rotation into three components, assigning portions to x, y and z axis that are mutually perpendicular. For bowling, the x-axis can be assigned to a line that is parallel to the foul line, the y-axis to the line parallel to the boards, and the z-axis to the vertical. Forward-roll is rotation about the x-axis, side-roll is rotation about the y-axis and mid-roll (or spin) is rotation about the z-axis. The pure full-roller delivery is a combination of forward- and side-roll only. Semi-rollers include spin. Spinners may have very little side roll. In a very strict physics sense, a ball may be delivered with rotation, but usually not in a roll, because that would imply complete traction. The technique of the great majority of bowlers involves a delivery that starts the ball in a skid that evolves into a roll that hooks into the pins.

A "full-roller" type of delivery does not hook as well as "3/4 rollers" on oily lanes. On successive rotations, the "full roller" repeatedly contacts the lane on the same full circumferential circle, on which the oil accumulates, making it harder for the side-roll to find traction and create hooking action. The "full-roller" had been the dominant choice before the changes in lane coatings and oil. The "semi-roller" is now preferred (it may also be called "3/4 roller" or by other slang terms). With a 3/4-roller a bowler puts the ball into a rotation whose contact ring is smaller, and on successive rotations enlarges (subsequent examination of the ball often shows a flaring of the circles of oil). This is because at every spot along the circle, friction reduces the rotation, and that includes the spin component, causing rotation on a continually larger circle. This has the effect of bringing relatively dry ball surface in contact with the lane, increasing traction for both forward-roll and side-roll. It probably goes without saying why bowlers often wipe oil off the ball.

Balance

Another effect of ball imbalance (either static or dynamic) is the ability to introduce gyroscopic effects on the rotation. The component of imbalance along the rotation axis provides a leverage that can change the orientation of the axis on its horizontal plane, an action physicists call precession. It is basically the same thing as a spinning toy top "going around in a circle." In the case of a rotating bowling ball, as it moves along the lane, there is only time for its total rotation axis to move along a short arc, but this is enough to reorient the total rotation so that some of the forward-roll becomes side-roll, increasing the side-roll provided in the bowler's delivery, thereby achieving more hook. It is possible to use dynamic ball balancing to achieve a stronger gyroscopic effect than static balancing alone.

The advent of dynamic ball balancing meant that bowlers could achieve "ball flare" without the need for a 3/4 roller delivery, and more hook. Additionally, balls with covers that create higher friction, such as "particle" balls, provide for more traction and hook. Bowlers are embracing these choices, buying balls whose characteristics complement or enhance their deliveries.

It is the opinion of many people in the bowling community that these advances in bowling ball technology have undermined bowling skill and have made it more difficult for lane maintenance personnel to lay out fair and credible conditions for participants. This is because advanced players using hi-tech balls "need" more oil to score high and might complain about the radical behavior of their balls on "dry" lanes. At the same time, less aggressive players might complain when they can not get their balls to hook. These complaints have been part of the game throughout USBC history. It has been a matter of which group prevails within the USBC—or what new technology comes along next.

Effect of ball structure on motion

RG (radius of gyration) and Differential of RG, plotted on orthogonal axes.

Various characteristics of ball structure affect a ball's motion throughout its skid, hook and roll phases.

Commonly used specifications relating to a bowling ball's core include radius of gyration (RG), differential of RG (commonly abbreviated differential), and intermediate differential (also called mass bias).

Analytically, the United States Bowling Congress defines RG as "the distance from the axis of rotation at which the total mass of a body might be concentrated without changing its moment of inertia".^[14] In practice, a higher RG indicates that a ball's mass is distributed more toward its cover—making it "cover heavy"—which tends to make the ball enter the roll phase later (further down the lane).^[15] Conversely, a lower RG indicates the ball's mass is distributed more towards its center—making it "center heavy"—which tends to make it enter the roll phase sooner.^[15]

Differential of RG is the difference between maximum and minimum RGs measured with respect to different axes.^[15] Differential indicates the ball's track flare potential, which describes how sharply a ball can hook.^[15] A higher differential indicates greater track flare potential—more angular motion from the break point to the pocket—and a lower differential indicates lower flare potential and a smoother arc to the hook.^[15]

The lesser-used intermediate differential rating (sometimes termed mass bias rating) quantifies the degree to which a bowling ball core is symmetrical or asymmetrical.^[15] Analytically, ID is defined by the USBC as the "difference in radius of gyration between the Y (high RG) and Z (intermediate RG) axes".^[14] In practice, a higher ID indicates greater asymmetry, which causes more area to be created at the break point to cause the ball to respond more quickly to friction than symmetrical balls.^[15]

Informally, a low-differential ball has been likened to one whose core is a spherical object (whose height and width are the same); a high-differential ball has been likened to a tall drinking glass (whose height and width are different); and a high-mass-bias ball has been likened to a tall drinking mug with a handle on the side (which has different widths in different directions).^[16]

Other elements of ball structure include surface texture (grit) and cover stock composition.

Manufacturers

• Ebonite International
• Brunswick
• Storm Products
• MOTIV Bowling
• ABS International
• DV8 Bowling
• Hammer Bowling
• columbia300
• Pyramid Bowling
• Radical Bowling
• Roto Grip Bowling
• Track Bowling