Dear Nick,
I don't mean to hate, but I feel that I need to point out a couple of observations with regards to this ball layout video. There is a conceptual/real problem in the method that you layout a bowling ball, and the people on this forum need to be aware of the differences in the outcome. Because I'm a geometry geek, and love talking about these things, this will get long. I apologize for that up front.
When talking about positive axis point in relation to the gripping holes on the ball, there is a universal method that pro shop operators use to locate that positive axis point. We first draw a centerline on the ball that splits the bridge and thumb hole in half. We then locate the grip center by measuring the span and dividing it in half (this process is up for a totally different discussion at another time). Measuring from either the fingers or thumb, we mark the grip center at one half of that span measurmement along the centerline. We then use the Pro Sect to draw a perpendicular line to the centerline at that mark. This line is called the grip midline. We extend this midline on the ball beyond the positive axis point that we have found using various methods (marking a thrown ball, using an armadillo, etc.). Finally, we draw a perpendicular line to the midline that intersects the positive axis point. This line is commonly referred to as the vertical axis line. We then note those positive axis point measurements as (blank) inches over x (blank) inches up or down.
I hope that everyone can agree on this so far. These are relatively simple concepts.
The problem with the layout video deals with the process of how you reversed your positive axis point measurements. In a situation where the bowler has a vertical coordinate measurement in their positive axis point (whether it's up or down), you must measure the vertical axis line measurement first, and then draw the perpendicular midline across the ball at the appropriate measurement. Finally, you draw your final perpendicular line at the appropriate distance to mark the centerline of your "grip to be." Your video showed you "reversing" the midline measurement first and then measuring a vertical measurement along the centerline of the grip. This process is not valid and does not result in the appropriate pin to axis measurements.
The problem with this method is that you are drawing perpendicular lines on the surface of a spherical object. If the bowling ball was flat, like a piece of paper, this method would be perfectly fine. But when you reverse the midline first, followed by the vertical measurement, you are changing the relationship of the pin to the bowler's positive axis point.
I tried a few examples here to give an example of what I'm talking about. All of these layouts were done with a 4 1/2" pin distance at a 50 degree layout, just like your video example.
I used your layout method with a 5 3/4" x 1/2" Up PAP. After using your method, I decided to layout the bowler's positive axis point using the process described above, which everyone uses in the pro shop world. When I draw the bowler's PAP using perpendicular lines on the bowling ball from the grip center found using your layout method, the PAP moves approximately 3/8" from the original location. Using a PAP of 5 3/4" x 1" Up results in a larger "miss" of 3/4".
I did two other examples using the 4 1/2" pin distance at a 50 degree angle. Using a 4 1/2" x 1/2" up PAP results in a "miss" of 1/4". Finally, using a PAP of 4 1/2" x 1" Up results in a larger "miss" of 1/2"
It's important to note that the size of the bowling ball does matter in this exercise. The Pro-Sect does not adjust for the size of the bowling ball, and the ball can range up to .095" difference in diameter. Pro shop operators and bowlers can try these examples that I've posed, but you may receive a slightly different measurement in the amount that the PAP moves.
Again, I hope people can see that the reason you must "reverse" the vertical measurement in a PAP first is because we are drawing lines on a spherical object. Also note that the longer your horizontal and vertical measurements measure, the larger the error would be in using this PAP reversing method. Your axis point measurements may be small enough to negate the error in most examples, but others will not.
In finishing, it's crucial to reverse the positive axis point in the appropriate manner so that you end up with the ball reaction you expected. In the example above of the bowler with a 5 3/4" x 1" Up PAP, I told you that the actual PAP moved by 3/4". In this example, the pin changed in relationship to the bowler's PAP by 3/4", and a 4 1/2" pin distance became 5 1/4". This would create a significant difference in ball reaction and may lead to undesirable results.
I hope that people understand this explanation, and if they have any questions about this process, I'll be glad to respond to them in this forum. Nick, I hope I didn't offend. I just want to educate people in these methods, and we need people to have the best understanding possible.
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Jeff Ussery
Powerhouse Training Clinics
www.proshoptraining.comEdited on 10/26/2006 11:16 AM
