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Author Topic: Asymmetry  (Read 2164 times)

LordWalrus

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Asymmetry
« on: January 19, 2010, 11:58:21 PM »
I've read that, after drilling, a ball with a symmetrical core becomes asymmetrical to some degree. That means the ball would have a mass bias after drilling, right? So... How assymetrical do these balls become? I would imagine only to a small degree, but is there any rule of thumb or average strength/rating of the mass bias in a symmetrical cored ball after drilling? I'm trying to get a feel for how comparable symmetrical balls and asymmetrical balls with low mass bias ratings really are.

Thanks!
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J_w73

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Re: Asymmetry
« Reply #1 on: January 20, 2010, 08:18:15 AM »
They do and the PSA ends up being at the thumb hole.  So even though the ball becomes assymetrical, the location of the PSA will not really have any asymmetrical effect on the rotation of the ball.  A weighthole on the other hand can add asymmetry that will effect the ball's dynamics depending on the location.
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16-17 mph,350 rpm,PAP 5 1/2 x 3/8up, HighGame 300 x 4, High Series 808
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icewall

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Re: Asymmetry
« Reply #2 on: January 20, 2010, 08:44:00 AM »
quote:
They do and the PSA ends up being at the thumb hole.  So even though the ball becomes assymetrical, the location of the PSA will not really have any asymmetrical effect on the rotation of the ball.  A weighthole on the other hand can add asymmetry that will effect the ball's dynamics depending on the location.
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16-17 mph,350 rpm,PAP 5 1/2 x 3/8up, HighGame 300 x 4, High Series 808
Book Average 205,PBA Xperience ave180



this is true for the most part (from what ive seen). usually the mass bias does end up NEAR the thumbhole or at it and even if the asymmetry was strong there because of the thumbhole size it would be too far away from the pap to have much effect on ball motion.

according to mo pinel the angle to the val has the most effect in creating asymmetry in symmetrical bowling balls BEFORE you move on to a weight hole. Obviously a weight hole would have the greatest effect.

Symmetrical Ball   
Drilling: 50°, Pin 5" from PAP, Different Angles to the VAL   
Angle to VAL   Low RG Axis   Asym Diff   Total Diff   
Undrilled               2.463     0.000     0.050   
20°                               2.469       0.008     0.051   
45°                               2.473       0.004       0.043   
70°                               2.475       0.004       0.041

this is the only other thing i know the link to off of my head is http://www.morichbowling.com/Drilling/The_Truth_about_Drilled_Balls.pdf
but it is about asymmetrical bowling balls and weighthole placement

and you could also watch the video promotion for the storm second dimension where hank boomershine puts 4 balls after drilling and determines their PSA showing you where it ends up!

http://www.youtube.com/watch?v=va1NdfLaOJ4
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dizzyfugu

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Re: Asymmetry
« Reply #3 on: January 21, 2010, 08:13:02 AM »
Do not confuse the core''s construction with the weight distribution inside of the ball.
What is key about "core asymmetry" is to understand that a core is placed through its drilling into an unstable rotational position (relative to the PAP, as reference), and that it will migrate towards a final and stable preferrential spin axis (PSA). This is true for both symmetrical and asymmetrical cores, or better: balls with low or high mass bias ratings.

In any ball these forces work the same - on strong mass bias balls, the PSA is normally an axis that goes through the MB marker, which has technically to be placed at 90° to the pin axis. That''s why such markers are placed 6.75" away from the pin, and they are marked because this "force" overrides other influences (see below).

This PSA migration is also true for symmetrical cores which may have a very low (or insignificant) mass bias rating of 0.01" or less (vague number). But here, the PSA is created through the CG shift, caused by the shifted core inside of the ball. Here, the marked CG comes into play, because it creates a rotational force much like in a "true" mass bias ball.
You can find the PSA on a low MB ball if you draw a 6.75" line from the pin through the CG. Where it ends up depends on the overall pin and CG placement, on stacked layouts it will normally end on the positive side of the thumb hole. You may mark it, and watch if the ball actually migrates from your PAP towards this PSA just before it enters the pins. It better should do so, otherwise, I''d wonder about the drilling setup or the release...

Anyway, drilled holes change the weight distribution, so strategically placed holes (or special depths) might affect and shift a PSA slightly.

And: from an asym. RG diff. (as a measure of the mass bias'' strength) of about 0.01" on, the core''s migration powers override the PSA effect created through the CG, so you better consider the MB marker''s placement instead of the CG when drilling up such a piece, even if it is a mild one. Placing the MB marker wrong can have VERY negative effects on the ball''s performance.
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Edited on 1/21/2010 9:28 AM

Edited on 1/26/2010 4:03 AM
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