Expert: - 1/23/2009

Question
QUESTION: Hello Chip,

I need to know why on some balls the MB mark isn't in the continuation of the Pin-CG line ?
Actually I have an Ebonite Big One with an MB position at 3” ½  of the left of the line coming from the Pin to the CG and at 6” ¾ from Pin, which is normal.
The Pin-CG distance is 2” ½.
Actually I have a trouble with it because I have a split or a crack ½” deep, coming from the ring finger hole, close to the Pin crossing the CG and following the Pin-CG line at almost 6” ¾ and I think that the Mass Biass is just under.

BR,
Vincent

ANSWER: Hello Vincent, I'm Warren.

The core sometimes shifts in production. Sometimes the manufacturer wants bigger pin out balls and creates a core/mold orientation where the center of gravity bumps away from the pin to mass bias "line".

While static weights are affected in the drilling, it is more important the Pin and Mass Bias are positioned where you want them. Often excessive static imbalance can be removed with a weight hole.

Ball layouts center on the Pin to Mass Bias line. CG location is of lesser importance. Thanks for the question. Did Chip have a good answer?

---------- FOLLOW-UP ----------

QUESTION: Hello Warren,

I agree with your comments but the purpose of my request was more concerning the physical explanation of how a MB can be far away from the line crossing the Pin and CG ?
In other words when the bowling ball builder positioned the MB, it will affect the position of the CG.
I don’t know how the MB is physically done, if it is a physical mass it is logical that its position is in the continuation of the line Pin-CG or close.
Why it is always at 6” ¾ distance from Pin, actually it is corresponding to the quarter (90°) of the ball ?

Otherwise I have no answer from Chip.

BR,
Vincent


Answer
Vincent,
You asked: I need to know why on some balls the MB mark isn't in the continuation of the Pin-CG line ?

You have an older ball that cracked. Are you needing to know because you suspect there is a problem or defect with the ball? You mentioned the crack but really didn't ask a question.

You understand that when building a ball the pin and Mass Bias locator pin are the two elements that allow a ball driller to know the orientation of the core inside the ball. The mass being identified for a driller is on the side of the core, 6 3/4 inches from the top (Pin) of the core. The intent is to be able to position an asymmetric protrusion of the core to help create ball reaction.

Further, when drawing a line from Pin to Mass Bias, I explained how a CG can end up positioned well off the line, and that the CG is an  identifier of a secondary influence (static weights).

When wrapping a core with the coverstock, material is injected into a mold.  If everything goes perfectly, Pin, Center of Gravity (CG) and MB should line up nicely. If the support rod holding the core in the intended position is bent (the hole it leaves becomes the Pin), the core turns a little when material is injected, the result would be a heavy spot that becomes the center of gravity (CG) off the "line"  connecting Pin to Mass Bias.

CG is only determined after production. It is a VERY SMALL part of ball layout and ball roll. The USBC rules on imbalance necessitate the identification of the CG (and often, in my experience they are still off, a little, from marked).

I hope this better answers your question. If you have a question about the cracked ball please ask it.