Static Weight Discussion.....Here we go again

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Static Weight Discussion.....Here we go again

Post by purduepaul »


Below I am going to discuss a topic near and dear to our hearts, static weights. Some companies have made their reputation on them while other companies simply say they do not matter. I will you give you FACTUAL evidence of why its my hypothesis that static weights play an insignificant factor in ball motion. Some of this I put in a post on another site, however I will add a little bit more evidence here.

Let's start at the beginning with
Bill Taylor (RIP)'s Balance book. I bought an original copy of
Balance off of amazon about two years ago after this topic appeared.
I believe its extremely important to look at historical data to see
what it says and see if it still is factual with current technology.
Bill Taylor assumes throughout balance that the imbalance weight is on
the OUTSIDE of the gyroscope (Balance pages 35,36,41, and 57). This
idea that the static imbalance of the ball is on the outer surface of
the ball is 100% FALSE.

This is proven wonderfully by Lane #1/AMF/900 Global's core CAD
designer Nick Siefers of AMF/900 Global. This article can be found
here http://www.900global.com/tech/BowlingBa ... tionDesign
The key CAD drawing you want to look at is Figure 2. This "imbalance"
really lies 0.037" from the geometric center of the bowling ball.
This is for a Pin to CG measurement of 3". This Scientifically PROVES
that the static imbalance is NOT on the outer surface of the ball.


Every major ball manufacturer has a certain internal box they have to
have the ending CG position in order for it to be statically legal.
The MAXIMUM distance away from the geometric center of the ball that
the ending CG can be is 3/64". This negates the myth that the static
imbalance of the ball lies on the outer surface of the ball.

So because the center of gravity is not the actual geometric center of the ball what is the total affect on the RGs. First let's cover where RG comes from. RG or Radius of Gyration comes from a mathematical calculation based on the objects moment of inertia (I). Moment of Inertia is a measure of how difficult it is to rotate an object, or in bowling how easy or hard it is to apply angular momentum and velocity to the object. Radius of Gyration is calculated by taking the square root of the Moment of Inertia about an axis divided by the weight. You are probably wondering, that's great and all but how does it apply to static weights.

In the 900 Global article cited above, remember how the center of gravity was really close to the geometric center of the ball? Well this affect the bowling ball's moment of inertias. Currently we only specify the Radius of Gyrations about three axes (X, Y, Z) but this is only part of the picture. Moment of inertia of ANY three dimensional object is stated as a tensor (three vectors on each principle axis) instead of one vector. So why do we only state three RGs instead of nine you ask? Because the other six, which is what the center of gravity displacement is small are negligible. The proof is attached below in the CAD work by Mr Steve Freshour of Washington, WV.

For this particular Double Thumb drilled Craze shown below lets go through the exercise of calculating the RGs for the Y axis in reference to the geometric center. This data can be found under moment of inertia taken at center of mass and aligned with output coordinate system. Note the y axis is the x axis and the x is really the y this is how the CAD program published the data.

RGyy= SQRT(99.4142/14.7638) = 2.595"

So when you take the three main values of the tensor Ixx, Iyy, Izz and calculate the RG it comes to a ball that has the following values.

RGx=2.535"
RGy=2.596"
RGz=2.563"

So this ball has a total differential of 0.061" and an intermediate differential of 0.033". Both of these values are drilled.

Now what do you think is the affect of center of gravity? It can be found by the difference between the RG values found above and the RG values calculated from the geometric center. Here are the RGs found from the geometric center found from the data found at the bottom of the first picture.

RGx=2.539"
RGy=2.595"
RGz=2.563"

So the effect of static weights on RGs are 0.004" on the X axis, 0.001" on the Y axis, and 0.000" on the Z axis.

The generally regarded standard deviation and error of the RG process is 0.004" So by the RG, static weights do not affect the RGs.

Let's prove this again in a different way. Let's look at two dual angle drillings on a symmetrical ball. This data has already been posted, but again proves that regardless of the Center of gravity position its where the holes intersect the core that determine the final RG values.

With Mr Freshour's assistance we took the same symmetrical cored undrilled bowling ball and drilled it two different ways with two vastly different CG positions.

One ball is 160 by 3 3/8" by 40 and one ball is drilled 50 by 3 3/8" by 40. This means that one ball will have the Center of gravity mark on the positive side of the ball and one ball will have the Center of gravity mark on the negative side. By the theory quoted above, these balls will have different RG values based on where the "mass" is placed. Here is the data

----Drilling---low RG----Total Differential-----Intermediate Differential-----RG about PAP
160 drilling------- 2.502"--------- 0.047"------------------ 0.008"-------------------- 2.517"
50 drilling-------- 2.502"--------- 0.046"------------------- 0.008"-------------------- 2.519"

These measurements are all within the standard error of the RG process which is 0.004" .

A lot to process, and a lot of DATA Enjoy!






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Re: Static Weight Discussion.....Here we go again

Post by MegaMav »

Amazing research Paul, Steve, Mo.
I really think this is the data and information everyone wanted to see.
I just hope that everyone can process the end game here.
Which is, the location of CG has an effect on dynamics less than that of the allowable amount of error in the study.

This would be called, statistically insignificant.

Good work, and thank you for efforts.
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Re: Static Weight Discussion.....Here we go again

Post by Mo Pinel »

MegaMav wrote:Amazing research Paul, Steve, Mo.
I really think this is the data and information everyone wanted to see.
I just hope that everyone can process the end game here.
Which is, the location of CG has an effect on dynamics less than that of the allowable amount of error in the study.

This would be called, statistically insignificant.

Good work, and thank you for efforts.
It was never said that static weights didn't matter at all. They are far less significant than mass properties. As always, great job, Paul. Concise and accurate.

By the way, get used to the bolding. It's always been part of my writings. Emphasis, you know. And I've been told that I can't get in trouble for doing it here.
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Re: Static Weight Discussion.....Here we go again

Post by MegaMav »

Mo Pinel wrote:
It was never said that static weights didn't matter at all. They are far less significant than mass properties. As always, great job, Paul. Concise and accurate.

By the way, get used to the bolding. It's always been part of my writings. Emphasis, you know. And I've been told that I can't get in trouble for doing it here.
Welcome in Mo.
I've been a fan of your products and knowledge for a very long time.
As I have told Paul and Steve, this is your sandbox, and stage to answer questions and provide information as you see fit.

We even have a wiki to document anything you wish. ---> http://wiki.bowlingchat.net/

You three, have full control of these Tech Forums, bold with pink in huge font if you want.
The stage is yours Mo, Steve, Paul.
Thanks for joining us, and for your time.
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Re: Static Weight Discussion.....Here we go again

Post by purduepaul »

I bumped this up so people could get caught up with this again....
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Re: Static Weight Discussion.....Here we go again

Post by JessN16 »

Paul,

You might have touched on it in the original post in the thread, but if you did it was part oft he physics that go over my head a bit.

I have one question to follow with: Has anyone studied the point at which statics do become significant? You and I have talked about this in chat before but I figured it would be nice to put it in a post that would have some staying power.

With the USBC seemingly ready to dump the static limits, surely there must be a point at which these things do have an effect. An ounce of sideweight would not, but a pound? I would think a pound would. Has you research produced a threshold at which these things matter?

If there is such a threshold, I would (a) expect the ball companies to begin designing in that direction, and certainly (b) a talented PSO with knowledge of how to manipulate the ball to be able to give a customer an advantage, similar to how a golf clubmaker (I also do that in my spare time, as well as drill my own stuff) is able to use weights to tune clubs to particular swingpaths.

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Re: Static Weight Discussion.....Here we go again

Post by kellytehuna »

I remember reading an article quite some time ago about what have come to be known as "Dodo balls." These balls were created by LITERALLY splitting two balls of different weight in half and splicing one half of each ball together, thus creating a "new" ball. These balls would have a HUGE imbalance (at a minimum, I would say 6oz or so). I would expect these balls would lope heavily down the lane and I suspect they tended to roll toward the heavier side of the ball. But that's speculation on my part. One other thing of note, is balls at this time didn't have "real" cores in the, so the ball was a solid mass, I believe.

I would not be surprised in the Kaufmann "Dodo" scales were invented because of these balls and I wouldn't be surprised if the static weight limits were introduced because of these balls, also.

I don't know what the minimum would be before static weights become an major factor in ball reaction, but I suspect it would be significantly more than the 1oz side and finger weight and 3oz of top weight we are currently restricted to. I would suspect if they loosened the rules to allow 3oz in any quadrant, you would see far fewer balls failing and you would only have to check a ball that has EXTREMELY weird CG placement. It's already been shown that a net difference of almost 3oz makes very little difference and any difference that is shown can't be DEFINITIVELY put down to static weights, because of potential differences in covers.

I'm not sure they should get rid of statics altogether, or we might see HUGE imbalances that will almost certainly affect ball reaction, but if they loosen them a bunch, as proposed above, I'm sure static weights will be much less of an issue than it is now and we can focus on what REALLY matters - knocking down those pins!
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Re: Static Weight Discussion.....Here we go again

Post by Old_Hickory »

1st USBC sets limits on the bowling balls out of the factor so I do not see this as an issue. The differential limit is .060. I wish they would get rid of the side weight limits because I hate putting a 1" hole in a ball 3 inches deep just to be able to lay the ball out like I want because the cg my be shifted a little right. Also, if they do this it will help the ball manufactures too. Mo will not have to call balls with cgs shifted over 1 and 3/4" blems (I think that is the measure he uses). Again lets get rid of it because in the grand skeem of things, it is not very relevant.

Does anyone know if they are going to throw it out? And if so is it going to happen in March 2011? Also if they do throw it out, what is the limit on balance hole sizes and depths?
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Re: Static Weight Discussion.....Here we go again

Post by JohnP »

The current limit on balance hole diameter is 1 1/4", there is no USBC limit on depth, but after you go past the center of the ball you start undoing the changes you made to the statics. -- JohnP
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Re: Static Weight Discussion.....Here we go again

Post by Old_Hickory »

The question is if they throw out the side weight and figure weight rules what is the hole size and depth limits going to be.
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Re: Static Weight Discussion.....Here we go again

Post by Mo Pinel »

Old_Hickory wrote:The question is if they throw out the side weight and figure weight rules what is the hole size and depth limits going to be.
I have been promoting limiting balance hole size of 1" diameter, 3" deep for two years. Manufacturers would not be able to manufacture a ball with > 4 oz. top weight.
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Re: Static Weight Discussion.....Here we go again

Post by triggerman »

since the posts on BR were deleted and no one really answered this question I will post it here for grins

symetrical cored ball, 15# 3 oz prior to drilling 3.50 top weight, (I have two identical) ball 1 has a 3" pin ball two has a 5" pin. I drill both balls 75 x 5 x 25 (for me this is pin above ring, cg stacked, roughly) I drilled fingers 2" deep on both balls, drilled 1" thumb on both balls 3 inches deep.................................why do they react differently (vastly different)

on edit and before we get carried away, this is a legitmate question not an attempt to stir the pot
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Re: Static Weight Discussion.....Here we go again

Post by rmack »

triggerman wrote:since the posts on BR were deleted and no one really answered this question I will post it here for grins

symetrical cored ball, 15# 3 oz prior to drilling 3.50 top weight, (I have two identical) ball 1 has a 3" pin ball two has a 5" pin. I drill both balls 75 x 5 x 25 (for me this is pin above ring, cg stacked, roughly) I drilled fingers 2" deep on both balls, drilled 1" thumb on both balls 3 inches deep.................................why do they react differently (vastly different)

on edit and before we get carried away, this is a legitmate question not an attempt to stir the pot

trig,

have you had both balls spun to confirm the drilled psa? the other item of note would be to make sure that both balls had the exact same surface... i almost never trust box surfaces.

i have a customer that has 3 identical riot zone pro 2.0's... exact same statics & dead weight, my dodo scale cannot see a difference between them. all roll differently, but after drilling, all have different post drilled spin times and ending psa locations... we ended up tuning cover prep to further separate the balls into a sensible arsenal (this guy does not like extra holes).

manufacturing tolerances can trump layout sometimes. weight holes can dominate layout as well ('specially in symmetricals). i am willing to wager that adding balance holes to both balls and ensuring identical cover prep would bring them much closer together. :)

just my .02
Last edited by rmack on October 25th, 2010, 7:51 pm, edited 1 time in total.
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Re: Static Weight Discussion.....Here we go again

Post by Mo Pinel »

triggerman wrote:since the posts on BR were deleted and no one really answered this question I will post it here for grins

symetrical cored ball, 15# 3 oz prior to drilling 3.50 top weight, (I have two identical) ball 1 has a 3" pin ball two has a 5" pin. I drill both balls 75 x 5 x 25 (for me this is pin above ring, cg stacked, roughly) I drilled fingers 2" deep on both balls, drilled 1" thumb on both balls 3 inches deep.................................why do they react differently (vastly different)

on edit and before we get carried away, this is a legitimate question not an attempt to stir the pot

I'll treat it as legitimate. Without a DeTerminator to find the exact PSA of the drilled ball and the spin time, we cannot begin to accurately analyze the cause and effect of the difference between the two balls. It could be in manufacturing or in the surface prep. as Paul mentioned.
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Re: Static Weight Discussion.....Here we go again

Post by bowl1820 »

This link appears to no longer work.

But you can find the article here:
http://www.itbca.bowlingknowledge.info/ ... top-weight

it has some slight changes and it's now called:
MANUFACTURING PROCESS VARIATION: THE SMALLEST of SHIFTS CAN ALTER PIN DISTANCE and TOP WEIGHT

the original version can be seen here:

Bowling Ball Production Design: Tolerances and Customer Driven Specifications
https://web.archive.org/web/20090901061 ... tionDesign
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Re: Static Weight Discussion.....Here we go again

Post by LabRat »

Since this thread has already been resurrected and referenced by several people, I thought I'd comment on it directly rather than start a new thread. The OP is below, with my comments in green.
purduepaul wrote:
Below I am going to discuss a topic near and dear to our hearts, static weights. Some companies have made their reputation on them while other companies simply say they do not matter. I will you give you FACTUAL evidence of why its my hypothesis that static weights play an insignificant factor in ball motion. Some of this I put in a post on another site, however I will add a little bit more evidence here.

Let's start at the beginning with
Bill Taylor (RIP)'s Balance book. I bought an original copy of
Balance off of amazon about two years ago after this topic appeared.
I believe its extremely important to look at historical data to see
what it says and see if it still is factual with current technology.
Bill Taylor assumes throughout balance that the imbalance weight is on
the OUTSIDE of the gyroscope (Balance pages 35,36,41, and 57). This
idea that the static imbalance of the ball is on the outer surface of
the ball is 100% FALSE.



No. Taylor modelled statics by assuming they acted as if they were on the outside of the ball, which is a perfectly reasonable, understandable and valid model. The fact we can modify statics by drilling holes on the outside of the ball clearly demonstrates the validity of this model.

This is proven wonderfully by Lane #1/AMF/900 Global's core CAD
designer Nick Siefers of AMF/900 Global. This article can be found
here http://www.900global.com/tech/BowlingBa ... tionDesign
The key CAD drawing you want to look at is Figure 2. This "imbalance"
really lies 0.037" from the geometric center of the bowling ball.
This is for a Pin to CG measurement of 3". This Scientifically PROVES
that the static imbalance is NOT on the outer surface of the ball.


No. The ENTIRE MASS of the ball acts at this point, 0.037" from the centre in your example. This is NOT the imbalance weight. This shift of the centre of mass CREATES the imbalance, which we call the top weight of the undrilled ball. This top weight behaves exactly as if it were added to the outside of a uniform sphere at the cg mark.

Every major ball manufacturer has a certain internal box they have to
have the ending CG position in order for it to be statically legal.
The MAXIMUM distance away from the geometric center of the ball that
the ending CG can be is 3/64". This negates the myth that the static
imbalance of the ball lies on the outer surface of the ball.


Wrong. You are conflating two different concepts here, as explained above.

So because the center of gravity is not the actual geometric center of the ball what is the total affect on the RGs.

Red herring. Statics don't affect ball motion (in theory) by changing rg's. The imbalance weight applies a torque to the ball, as per 'Balance'.

First let's cover where RG comes from. RG or Radius of Gyration comes from a mathematical calculation based on the objects moment of inertia (I). Moment of Inertia is a measure of how difficult it is to rotate an object, or in bowling how easy or hard it is to apply angular momentum and velocity to the object. Radius of Gyration is calculated by taking the square root of the Moment of Inertia about an axis divided by the weight. You are probably wondering, that's great and all but how does it apply to static weights. It doesn't.

In the 900 Global article cited above, remember how the center of gravity was really close to the geometric center of the ball? Well this affect the bowling ball's moment of inertias. Currently we only specify the Radius of Gyrations about three axes (X, Y, Z) but this is only part of the picture. Moment of inertia of ANY three dimensional object is stated as a tensor (three vectors on each principle axis) instead of one vector. So why do we only state three RGs instead of nine you ask? Because the other six, which is what the center of gravity displacement is small are negligible. The proof is attached below in the CAD work by Mr Steve Freshour of Washington, WV.

For this particular Double Thumb drilled Craze shown below lets go through the exercise of calculating the RGs for the Y axis in reference to the geometric center. This data can be found under moment of inertia taken at center of mass and aligned with output coordinate system. Note the y axis is the x axis and the x is really the y this is how the CAD program published the data.

RGyy= SQRT(99.4142/14.7638) = 2.595"

So when you take the three main values of the tensor Ixx, Iyy, Izz and calculate the RG it comes to a ball that has the following values.

RGx=2.535"
RGy=2.596"
RGz=2.563"

So this ball has a total differential of 0.061" and an intermediate differential of 0.033". Both of these values are drilled.

Now what do you think is the affect of center of gravity? It can be found by the difference between the RG values found above and the RG values calculated from the geometric center. Here are the RGs found from the geometric center found from the data found at the bottom of the first picture.

RGx=2.539"
RGy=2.595"
RGz=2.563"

So the effect of static weights on RGs are 0.004" on the X axis, 0.001" on the Y axis, and 0.000" on the Z axis.

The generally regarded standard deviation and error of the RG process is 0.004" So by the RG, static weights do not affect the RGs.

Let's prove this again in a different way. Let's look at two dual angle drillings on a symmetrical ball. This data has already been posted, but again proves that regardless of the Center of gravity position its where the holes intersect the core that determine the final RG values.

With Mr Freshour's assistance we took the same symmetrical cored undrilled bowling ball and drilled it two different ways with two vastly different CG positions.

One ball is 160 by 3 3/8" by 40 and one ball is drilled 50 by 3 3/8" by 40. This means that one ball will have the Center of gravity mark on the positive side of the ball and one ball will have the Center of gravity mark on the negative side. By the theory quoted above, these balls will have different RG values based on where the "mass" is placed. Here is the data

----Drilling---low RG----Total Differential-----Intermediate Differential-----RG about PAP
160 drilling------- 2.502"--------- 0.047"------------------ 0.008"-------------------- 2.517"
50 drilling-------- 2.502"--------- 0.046"------------------- 0.008"-------------------- 2.519"

These measurements are all within the standard error of the RG process which is 0.004" .

A lot to process, and a lot of DATA Enjoy!

Studies by Kegel on the effect of lane topography have shown that a continuous slope of 40/1000", the maximum allowed, causes a deviation of 1.2 boards over the length of the lane, for a 'good' bowlers stats. See http://www.11thframe.com/news/article/6743" onclick="window.open(this.href);return false; and links within.
The slope affects the ball path because the centre of gravity is not directly above the lane contact point, generating a sideways force, which for a sphere is effectively a torque about the contact point.This slope moves the cg by a distance of 0.00425" from directly above the lane contact point, equivalent to about 0.25oz. imbalance weight. A knowledgeable ball driller can use ball flare to get the ball into the roll phase with effectively 3oz. side weight. The Kegel data and the data from the USBC static weight study suggest to me that this can have a profound effect on entry angles and continuation through the deck, and I still maintain this is likely to be the best explanation for the difference between the MOhole and double thumb drills.
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