Manufacturing Process Variation:The smallest of shifts can alter Pin Distance and Top Weight

MANUFACTURING PROCESS VARIATION:
THE SMALLEST of SHIFTS CAN ALTER PIN DISTANCE and TOP WEIGHT

Nick Siefers, Senior Design Engineer, This email address is being protected from spambots. You need JavaScript enabled to view it.

At 900 Global we strive to produce not only high performing bowling balls on the market but also high manufacturing quality.  We listen to our pro-shops and bowlers, and then design products to meet their needs.  During the design and development phase many variables are analyzed and tested to verify that during production the ball of choice can be produced with minimal deviations from the target.  However, due to natural and inherent variations in the process not all bowling balls are made at the specified design target.  The following information concentrates on explaining why final pin distance and top weight can vary from ball to ball.

 

            The center of gravity of a bowling ball is the point at which, if the ball was suspended, it would be perfectly balanced in all directions.  Bowling ball manufacturers mark this spot on the surface of the bowling with an indication logo.  However, this surface mark is not the actual center of gravity of the bowling ball.  The true center of gravity of the ball lies deep inside the shell and is very close to the center of the ball.  Figure 1 shows and example of the actual CG distance from the center of the ball.  For the Break & Eagle bowling balls the center of gravity is only .037 inches from the center of the ball.  In geometry, connecting two points in 3D space is called a “Vector”.  If the vector from the center of the ball through the actual CG is extended to the ball surface, this is the location for the CG indicator.  Figure 2 below shows this extended vector. 

 

 

 

 

 

Figure 1:  Magnified center of bowling ball via CAD

 

 

 

 

 

 

 

 

 

Figure 2: Actual CG and Surface CG Indicator

 

 

 

     Design engineers then can move the core vertically and horizontally inside the shell to change the actual center of gravity of the bowling ball. This changes the position of the CG mark.  Again, the actual CG is located almost at the center of the bowling ball.

 

            The Pin to CG distance is important for ball drillers to create different ball motions.  The “Pin” is both the top of the inner core assembly and typically the lowest RG axis of the bowling ball.  It is the distance from this Pin location to the CG mark that is commonly referred to as the “Pin Distance” of the bowling ball.  Different pin distances give the consumer optimum performance ranges and drilling options for the many types of players.       

 

Top weight is defined as the amount of imbalance of weight between the “Pin” side and opposite side of the bowling ball.  USBC regulations allow 3 ounces of top weight after drilling.  Small movements of the core inside the shell affect the pin distance but it also affects the amount of overall top weight as well.

 

These small changes can drastically alter the top weight and pin distance. In a perfect world, the designed pin distance of 3 inches and 2 ¾ ounce top weight would be produced 100% of the time.  However, in reality, production variance occurs.  Production variance can come from a wide range of causes.  All components from the inner core to the shell must be in a specific place to have the center of gravity in the correct location.  During the production of a ball there are several steps and all steps have some error.  The error from each step compounds together to alter the CG location and change the top weight and pin distance.  This does not mean that the resulting ball is “bad/less superior”, but rather means that every ball will not be exactly the same.  Below are some examples of how small changes in the Break & Eagle core location affect the final product.

 

By design, the top portion of the inner core for the Break & Eagle must be placed at exactly 3.11 inches from the center of the ball and the top of the outer core must be exactly placed at 3.80 inches from the center of the ball to yield a 3 inch pin and 2 ¾ ounce top weight.  The computer aided design (CAD) drawing below illustrates these dimensions.

 

 

 

 

 

Figure 3:  The Break/Eagle  15# “Ideal” Design Dimensions

 

 

 

The following figure shows the results if these two dimensions are missed by the smallest of margins in the same direction (core closer to pin side).  It can be seen that by a miss of only 1/10th of an inch in exact placement of the core, the overall pin distance and top weight is affected and changed by over ¾ of an inch and ¾ of an ounce in top weight.

 

 

 

 

The Break & Eagle: 15# Design

 

 

 

 

Top of Inner Core ('')

Top of Outer Core('')

Pin Distance('')

Top Weight(oz)

Actual CG from Center of Ball ('')

 

3.11

3.8

3.00

2.73

0.0368

 

3.13

3.82

2.77

2.88

0.0388

 

3.15

3.84

2.61

3.03

0.0408

 

3.21

3.9

2.21

3.51

0.0472

Total Change(in):

0.1

0.1

0.79

0.78

0.0104

 
Figure 4: Core Location Dimensions and Resulting Pin/Top Weight

 

             

 

            The figure shows the final pin distance and top weight changes from a very small core movement.  When the core position changes, regardless of the reason, it results in the actual center of gravity moving by small amounts but has large impacts on the final ball.

 

This example only looked at moving the core vertically toward the pin.  In another example, the following chart shows the magnitude in CG, Pin distance, and top weight changes from the core assembly tilting (not perfectly straight up and down) by only 1 degree from the vertical.

 

 

 

 

The Break & Eagle: 15# Design

 

(Core Vertically/Horizontally in Correct Position)

 

Core Tilt (Degrees)

Pin Distance('')

Top Weight(oz)

Actual CG from Center of Ball ('')

 

0

2.80

2.66

0.0357

 

 1/2

3.45

3.04

0.0410

 

1

3.94

3.49

0.0470

Total Change:

1

1.14

0.83

0.0113

 

Figure 5:  Tilt Variance and the Resulting Pin/Top Weight

 

 

 

 

 

All of these characteristics present manufacturing challenges and engineers work to minimize the variables that create variance in an effort to produce the “ideal” bowling ball.  Engineers use many types of analysis and design factors to bridge the gap between production variance and desired product results.  Reducing variance is key to meeting customer demands and manufacturing a high quality product that lives up to its name. 

 

Hopefully this in depth look at the manufacturing process helps to explain the final product results.  In theory and in design each ball would be manufactured to have the ideal pin distance and top weight but process variation prevents this from occurring 100% of the time.  Although shifts in pin distance and top weight should be expected, the end result provides a greater number of options to drill the bowling ball based upon what the pro-shop operator is seeking to accomplish with the customer.