Ive worked in a pro shop for about 4 years now so i would consider myself qualified to answer your questions.
A) Not really sure what you are talking about right here, but if i understand correctly, you are talking about placing the CG on the Negative side of the ball? Here is a pic of my No Mercy Beatn' which has the CG on the negative side of the ball, is this what you are referring to?
http://ryman624.googlepages.com/Mercy2.JPGIf this is what you are talking about, well there are a few reasons for this and it can get a little complicated for someone who doesn't know too much about layouts, but I will give it a go as simply as i can.
1) If you are laying the ball out so that the drill pattern is 5x5, that is, pin is 5 inched from PAP and CG is 5 inches from PAP, and your PAP measurements are less than 5 inches lateral (to the right if you are a righty or left if you are a lefty), then measuring 5 inches over from your PAP will put the CG on the negative side of the bowling ball.
2) With the case of my No Mercy Beatn', we dont take the CG into account at all. With the Beat'n, there is a specific drilling that is recommended to use to get the most out of the bowling ball. That drilling is to keep the Mass Bias (which is the Heart with a white pin in it on this particular ball) on the negative side of the ball, specifically located on the start of your track. Because this is the recommended layout, some balls will have the CG on the negative side of the ball, like mine has. This is OK to have on high end equipment because you deal more with the Mass Bias than you do with the CG.
3) With other bowling balls (not including the No Mercy line or The One line), placing the CG (and or the MB) on the negative side of the ball will create an early rolling ball motion.
B) Mass Bias. Mass Bias can be found three different ways. The first way is to purchase a high end bowling ball, which has the Mass Bias already marked on the surface of the ball, like my No Mercy has. The way to locate the Mass Bias on a mid line bowling ball which does not have a mass bias rating because its core shape is Symmetric is to draw a line from the pin through the CG which is 6 3/4 inches long. That point would be your invisible mass bias.
C) With the high end bowling balls, the Mass Bias location will depict, for the most part, your bowling balls reaction on the lane. This is where it can get confusing because there are many factors in laying out the bowling ball, and three different ways in which you can move the mass bias to dictate ball reaction. To give a quick run through, picture a bowling ball. On one side of the ball you have your PAP. Now imagine that PAP directly on the other side of the ball, this is your NAP, or negative axis point. The closer you shift the MB towards your PAP, the earlier your ball will begin to pick up its roll. As you shift the Mass Bias towards the middle point between your PAP and NAP, you will create more backend snap.
If you are changing the location of the Mass Bias while laying out the ball, you will be changing both the Degree angle and Mass Bias to PAP distance, but the Pin to PAP does not have to change. The tools available to pro shop owners and regular Joe Schmoe's are what will help you keep your Pin in the same distance while shifting your Mass Bias. Basically, then laying out a ball, you can take a Quater Scale, place the 0 marking on the pin, place your greece pencil on the number which you want to utilize as your Pin to PAP distance, and draw an arc. Now your Pin to PAP distance is set at whatever distance you please. Now all you have to do is decide how far you want your Mass Bias to PAP to be, and draw an arc the same way, and where the two arc's intersect is your PAP. So you can change the Mass Bias to wherever you want it once you have the arc for the Pin to PAP drawn on the ball.
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