win a ball from Bowling.com
« previous next »
Pages: [1] 2

Author Topic: Is this possible?  (Read 4532 times)

Moon57

  • Hero Member
  • *****
  • Posts: 745
Is this possible?
« on: May 30, 2008, 09:41:39 PM »
Got my x-blem Cell yesterday. Box is marked .63 topweight, cg is 2" to the right of the pin-mb line. Start checking the cg on my digital homebrew scale and the cg doesn't seem to be in the right spot. Put the ball in the spinner with the cg straight up to check for wobble, spinner shakes pretty good. Keep moving ball around in spinner until the ball is spinning nice smooth and mark the top of the ball. Put the ball back on the scale and now the ball has 1.3 oz of top weight and the cg that I marked is 1 1/2" to the left of the pin-mb line. Is it possible the cg is off by 3 1/2" and the topweight is off by .7oz? I never thought about it before but how is the cg determined at the factory?
--------------------
Moon
--------------------
So many questions, so little time but I''m having fun.
Logged

 

Russell

  • Hero Member
  • *****
  • Posts: 5121
Re: Is this possible?
« Reply #1 on: May 31, 2008, 05:50:11 AM »
Sometimes a blem is due to a mismarked CG.  Just measure it a couple of times on the scale, remark it with a tool in the shop, and drill away.
--------------------
http://www.myspace.com/rlrussell

The artist formerly known as "jabroni"
Logged

1MechEng

  • Hero Member
  • *****
  • Posts: 1679
  • Bowling Nerd Herd member
Re: Is this possible?
« Reply #2 on: May 31, 2008, 06:00:52 AM »
If I remember correctly, Roger (aka Mustang Guy) said that there was a batch of mismarked cells that went out.
You might PM him, and also do a search on this site (in the archives) for the previous thread that discussed this.
--------------------
======================
Dan
======================
Engineering * Bowling = a fun and practical application of rotational kinematics.

Bowling Nerd Herd (TM) Member
Logged
Dan

T-GOD

  • Hero Member
  • *****
  • Posts: 2141
Re: Is this possible?
« Reply #3 on: May 31, 2008, 11:47:27 AM »
Just because the ball doesn't wobble in the spinner, doesn't mean the CG is where you marked it. It may just be where the core is most stable. To find the CG go to... http://www.lane1bowling.com/tech/cg.html =:^D
Logged

Moon57

  • Hero Member
  • *****
  • Posts: 745
Re: Is this possible?
« Reply #4 on: May 31, 2008, 08:53:13 PM »
T-, am I correct in saying that the cg is the stacticaly heavy spot on the ball? Doesn't it make sense that if this heavy spot is at the top and is lined up with the ball spinner cup shaft that the ball won't wobble? Now imagine the heavy spot being at a right angle to the cup shaft wouldn't it now make sense that the spinner would try and wobble? The dynamics of the core really don't come into play, just how the weight distribution of the core affects the cg. If I am missing something here please explain it for me so I can see why I'm wrong.
--------------------
Moon
--------------------
So many questions, so little time but I'm having fun.

Edited on 5/31/2008 8:53 PM
Logged

Doug Sterner

  • Hero Member
  • *****
  • Posts: 4395
Re: Is this possible?
« Reply #5 on: May 31, 2008, 09:01:26 PM »
core dynamics will overcome a topweight difference of even 2-3 oz so your wobble is most likely due to the core creating an imbalance as oppposed to the top weight.
--------------------
Doug Sterner
Doug's Pro Shop
Owego, NY
http://dougsproshop@aol.com
www.dougsproshop.net
Lane 1 Buzzsaw...The Official Power Tool Of Bowling
Logged
Doug Sterner
Doug's Pro Shop
Owego, NY

Proud Member of the NRA
Fighting to uphold the Constitution of the U.S.

BigWillyStyle

  • Hero Member
  • *****
  • Posts: 897
Re: Is this possible?
« Reply #6 on: May 31, 2008, 09:11:27 PM »
quote:
T-, am I correct in saying that the cg is the stacticaly heavy spot on the ball? Doesn't it make sense that if this heavy spot is at the top and is lined up with the ball spinner cup shaft that the ball won't wobble? Now imagine the heavy spot being at a right angle to the cup shaft wouldn't it now make sense that the spinner would try and wobble? The dynamics of the core really don't come into play, just how the weight distribution of the core affects the cg. If I am missing something here please explain it for me so I can see why I'm wrong.
--------------------
Moon
--------------------
So many questions, so little time but I'm having fun.

Edited on 5/31/2008 8:53 PM


Picture it like this....imagine that the core is shaped like a heart (like a valentine's day heart...not an actual human one). Actually, let's use the Gas Mask core, since it's very large at one end and smaller at the other.

http://123bowl.com/ball.asp?ballid=2871

Imagine that even if you flip the core over 180 degrees, that the ball will still spin the same, since the cg would still be lined up with the shaft. This is why thi test isn't 100% accurate.

Big Willy Style
--------------------
Just my $0.02 so take it for what the Foreign Exchange values it at!
"I was raised by a cup of coffee..."
***This message brought to you by the A.O.B.U.B.O.A. (Assembly Of Back-Up Bowlers Of America) which is now taking applications***  
Honorary Member of the F.O.S. (and also the best back-up bowler the Saws have ever had)!
Visionary Test Staff Member '08-'09
Logged

Moon57

  • Hero Member
  • *****
  • Posts: 745
Re: Is this possible?
« Reply #7 on: May 31, 2008, 09:27:41 PM »
Doug, the way I'm looking at it there are no core dynamics when the core is forced to spin on the fixed axis of the ball cup shaft. I agree about the dynamics when the ball is rolling on the alley.

BigWilly, your right, if you took the cg and put it right on the bottom it wouldn't wobble. But the cg would still be lined up with the ball cup shaft. So you could have a possible 2 spots for the cg but a quick check on the scales would tell which is which.

I need to ask a question, does the static weight distribution in the core affect the cg? It seems like it would but nobody has actually stated it does.
--------------------
Moon
--------------------
So many questions, so little time but I'm having fun.
Logged

JohnP

  • Hero Member
  • *****
  • Posts: 5819
Re: Is this possible?
« Reply #8 on: June 01, 2008, 08:45:16 PM »
When you are spinning the core at a fixed orientation other than a stable one, the forces required to hold it stable cause the vibration.  The physics are trying to force the ball to move toward a stable rotational axis.  Use the method T-GOD referred you to, determine the true cg, and you'll see that it's not the cg causing the vibration.  --  JohnP
Logged

JessN16

  • Hero Member
  • *****
  • Posts: 3716
Re: Is this possible?
« Reply #9 on: June 01, 2008, 09:10:32 PM »
Since this is a MB ball, is the MB not affecting this issue as well?

Jess
Logged

Moon57

  • Hero Member
  • *****
  • Posts: 745
Re: Is this possible?
« Reply #10 on: June 01, 2008, 10:55:27 PM »
Say John, did you happen to click on TGOD's find the cg link? I couldn't figure out how to do it on a RotoGrip ball.  When the cg is lined up with the ball cup shaft the core is in a stable position. The only thing that gives the core any dynamics is how the weight is distributed within the core in regards to the centerline of the ball.

Jess, yes the mb does affect the cg. Stop and think about it, the mb is there because one side of the core is heavier than the other, or the core is offset from the centerline of the ball. But it all boils down to the internal weight distribution of the ball.

I've never used a regular bowling ball scale but I'm assuming, correctly I hope, that when finding the cg it winds up at the top of the ball while it's sitting in the scale. Now, as long as you keep the cg exactly at the top of the ball you can rotate the ball to any position and it will always be in balance on the scale. Since that can be done, it doesn't matter if you rotate the ball at 1 rpm or 500 rpm. The ball will always be in balance if the cg is at top of the ball. Of course the shaft of the ball cup on the spinner has to be absolutely vertical.
--------------------
Moon
--------------------
So many questions, so little time but I'm having fun.
Logged

dizzyfugu

  • Hero Member
  • *****
  • Posts: 7606
Re: Is this possible?
« Reply #11 on: June 02, 2008, 09:01:33 AM »
quote:
Since this is a MB ball, is the MB not affecting this issue as well?

Jess


That's the problem - the ball in the spinner (or determinator) will move towards its MB, its preferred spin axis. But this does not tell you anything about the actual CG placement. IMHO, you'd need a do-do scale for this task, since it is a static weight issue.
--------------------
DizzyFugu - Reporting from Germany

Confused by bowling?
Check out BR.com's vault of wisdom: the unofficial FAQ section
Secrets revealed: What's a fugu?
Logged
DizzyFugu ~ Reporting from Germany

All10

  • Jr. Member
  • **
  • Posts: 94
Re: Is this possible?
« Reply #12 on: June 02, 2008, 09:42:47 AM »
You want the CG at the top of the scale as you put if so that "IF" you rotate the ball 90, 180, 270 degrees the ball is still statically balanced. If the CG is not at the top center, the scale will not stay level when the ball is rotated, since the heaviest static spot is now in a different place.

Once a bowling ball starts spinning like in a spinner the core want's to make the ball spin to its prefered axis, you just need to spin the ball fast enough for it to overcome friction with the ring on the spinner. That is your vibration.
Logged

JohnP

  • Hero Member
  • *****
  • Posts: 5819
Re: Is this possible?
« Reply #13 on: June 02, 2008, 10:31:24 AM »
Moon -- The procedure will work on any ball, not just Lane 1's.  They, of course, use their balls in their illustrations.  They refer to the orientation of their diamond label, but only to show how to rotate the ball.  If it helps, draw a diamond around the marked cg and pretend it's a Lane 1 ball.  Then follow their instructions.  The true cg will end up near, but not necessarily dead on, the top of the ball.  Its location depends on where you draw the first line.  --  JohnP
Logged

Moon57

  • Hero Member
  • *****
  • Posts: 745
Re: Is this possible?
« Reply #14 on: June 02, 2008, 01:13:40 PM »
John, my bad for not reading the instructions. I went back and reread it and understand what they are talking about now. Thanks for bringing my attention to that.
--------------------
Moon
--------------------
So many questions, so little time but I'm having fun.
Logged
Pages: [1] 2
« previous next »