Mismarked mass bias?

[RobbieB]

So I have a 13lb Pure Physics ball here to drill, only 1" pin out, and the cg appears to be correctly marked. However, the pin to mass bias distance is only 4''! - pretty much on a line through pin & cg.
Is the Pure Physics symmetric in 13lb? I know mb location is more of a tweaking tool, but I'm not a great fan of punching this out if the mb could be a couple of inches out in either direction.
Anyone else seen this? And can anyone confirm that the mb should still be 6 3/4 from the pin even in assymetric balls (just not always through the cg) cos if it is I can probably find the correct location on the dodo.

Seemed a little odd, first time I have seen a ball this obviously mismarked make it through QC. Or is it possible to have only a 4" mb - pin distance in an assymetric ball? I didn't think it was, by definition.

Cheers, Robbie.

 

[tonx]

Ohh nice one mate, but one that I am surprised that you have asked and you are right! The key to answering it yourself, is to ask what a MB/PSA is.

The mass bias mark is to indicate the high rg axis' greatest point of bias or influence. It's effect is the same concept* as a small weight added to the side of a spinning top. While the top is at full speed its spin axis is not really going to be affected due to centrifical force, as the top slows down it will have a tendancy to stop on the weighted side.

The true MB/PSA of an undrilled ball must be on the high rg axis of the core which is at 6 3/4 from the low rg axis (the PIN).

Without a DeTerminator machine, you cannot locate the true MB/PSA of the undrilled core. However the strength of the Pure Physics's int. diff. needs to be considered, and if not significant just use a balance hole to change the breakpoint shape for your customer.

The bigger question is, how a ball could have a MB/PSA marker mismarked, because in Ebonite made balls it is marked even before pouring the filler on the 90degree axis of the core mould. I'd say either the pin or the MB/PSA has been plugged and moved after completely pouring the balls the first time. I have heard of this to make pin request quota, but that manufacturer was not Ebonite.

*An MB/PSA is a little unlike the spinning top on modern bowling balls. It is not weight that creates asymmetry, but rather the Mass of the shape that creates a psa in a ball core.

 

[RobbieB]

Ohh nice one mate, but one that I am surprised that you have asked and you are right! The key to answering it yourself, is to ask what a MB/PSA is.

The mass bias mark is to indicate the high rg axis' greatest point of bias or influence. It's effect is the same concept* as a small weight added to the side of a spinning top. While the top is at full speed its spin axis is not really going to be affected due to centrifical force, as the top slows down it will have a tendancy to stop on the weighted side.

That is a horrible analogy for mass bias effect - especially as a ball is generally going to increase rotational speed, not slow down. Also, mass bias can't affect a ball that starts off on the low rg axis (pin axis drilling) like a top. But, anyway:

The true MB/PSA of an undrilled ball must be on the high rg axis of the core which is at 6 3/4 from the low rg axis (the PIN).

Without a DeTerminator machine, you cannot locate the true MB/PSA of the undrilled core.

You can, actually - it is just a very tedious process. My fellow geek Dousty probably knows how.

However the strength of the Pure Physics's int. diff. needs to be considered, and if not significant just use a balance hole to change the breakpoint shape for your customer.

The bigger question is, how a ball could have a MB/PSA marker mismarked, because in Ebonite made balls it is marked even before pouring the filler on the 90degree axis of the core mould. I'd say either the pin or the MB/PSA has been plugged and moved after completely pouring the balls the first time. I have heard of this to make pin request quota, but that manufacturer was not Ebonite.

*An MB/PSA is a little unlike the spinning top on modern bowling balls. It is not weight that creates asymmetry, but rather the Mass of the shape that creates a psa in a ball core.

If it was (accurately?) marked after pouring, I could see it being a dud core - where the pin is not actually the low rg axis. It certainly doesn't look as though anything has been moved. Quite odd, really. I might take a pic and post it.

 

[tonx]

That my way of simplifying the process of a psa's effect. Don't like it don't use it.

I'll also be as impressed as the rest of the industry will be if you can locate a PSA with a dodo... In fact sell your concept to the manufacturers as they can't do it at the moment, but im sure such a geek like yourself can create some magical way to do it.

No really, you can't, because you can't measure mass with a scale. Sorry mate, but you are wrong on this one.

 

[RobbieB]

Who said anything about using a dodo?

 

[tonx]

Anyone else seen this? And can anyone confirm that the mb should still be 6 3/4 from the pin even in assymetric balls (just not always through the cg) cos if it is I can probably find the correct location on the dodo.

You did man....

 

[RobbieB]

lol yeah, not thinking about the first post when I wrote that - but you don't need a determinator. Just have to string up a torsion type setup similar to how they measure rg of pins. Three bits of string, big ball ring and a stopwatch.

 

[tonx]

And a very very long time, and lots of patience.....

In the bowling world, that's called an RG-Swing.

There are also rumours around the industry that a crude determinator has been made, which might save you a few hours on an rg swing

 

[bluey]

Hey Robbie, just drill the ball for a left hander, you know that it's soooo easy on my side it wouldn't matter how the ball layout was done.

 

[RobbieB]

Hey Bluey - if it was for a lefty, I wouldn't care how it reacted.