Just for fun, How round is a billiard ball?

L.S. Dennis

L.S. Dennis

Well-known member
Apparently not as round as you think! Here's something Bob and Dr Dave might enjoy. The following is an excerpt for Mike Shamos's wonderful book entitled, 'Pool History, Strategies, and Legends.' In it he states:

"It is said that the earth is relatively smoother than a billiard ball. Here is what that means: A ball is permitted to vary by .005 inches out of a typical diameter of 2.25 inches, which is about 1 part in 500. The greatest depth in the ocean and the height of the tallest peak earth are both around 30,000 feet, which calculated with a diameter of 8,000 miles amounts to about 1 part in 750, much less significant than the variance on a billiard ball"!

Looks like Aramith is going to have to go back to the drawing board!
 
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L.S. Dennis said:
Apparently not as round as you think! Here's something Bob and Dr Dave might enjoy. The following is an excerpt for Mike Shamos's wonderful book entitled, 'Pool History, Strategies, and Legends.' In it he states:

"It is said that the earth is relatively smoother than a billiard ball. Here is what means: A ball is permitted to vary by .005 inches out of a typical diameter of 2.25 inches, which is about 1 part in 500. The greatest depth in the ocean and the height of the tallest peak earth are both around 30,000 feet, which calculated with a diameter of 8,000 miles amounts to about 1 part in 750, much less significant than the variance on a billiard ball"!

Looks like Aramith is going to have to go back to the drawing board!
Click to expand...
Cool stuff. At last year's BCA Hall of Fame dinner in Norfolk, VA, I sat next to Mike Shamos. It was the first time I'd seen him in about a decade. Mike, who is a professor at Carnegie Mellon University in Pittsburgh, is a really interesting guy to be around and is, without question, one of the smartest guys that has ever graced pool with his presence.
 
L.S. Dennis said:
Apparently not as round as you think! Here's something Bob and Dr Dave might enjoy. The following is an excerpt for Mike Shamos's wonderful book entitled, 'Pool History, Strategies, and Legends.' In it he states:

"It is said that the earth is relatively smoother than a billiard ball. Here is what means: A ball is permitted to vary by .005 inches out of a typical diameter of 2.25 inches, which is about 1 part in 500. The greatest depth in the ocean and the height of the tallest peak earth are both around 30,000 feet, which calculated with a diameter of 8,000 miles amounts to about 1 part in 750, much less significant than the variance on a billiard ball"!

Looks like Aramith is going to have to go back to the drawing board!
Click to expand...
Ah, but the earth is an ellipsoid, not a sphere. The "diameter" is about 70,000 feet longer at the equator than pole-to-pole.

Dave (oops, missed Cuedup's reply ! )
 
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The cheap-O Chinese 8-ball I've had soaking in a bucket of soapy water measures 2.233" in diameter, and the runout, as near as I can measure with a dial caliper (which isn't a very accurate way to do things), is 0.0005". That is only .5/1000" variation in roundness.

So I guess you could call it a little small, but reasonably round (that's what she said).

original.jpg
 
The idea of creating a perfectly round sphere is a topological problem.

In terms of producing the billiard ball more roundly the construction techniques would have to evolve.

Equally worth arguing is the roughness or smoothness of the surface area on the balls. The balls are coated with a smooth finish. If instead it had a slight texture, I think it would help roll over table impurities. Would it solve skids maybe some.

Each improvement should being a clear advantage to the game. Fixing skids and golden breaks may or may not be solved by Aramith.


Shamos and Jewett were the two names mentioned in Byrnes book. Byrnes book was my pool bible for more years than should have been.
 
Banger said:
The cheap-O Chinese 8-ball I've had soaking in a bucket of soapy water measures 2.233" in diameter, and the runout, as near as I can measure with a dial caliper (which isn't a very accurate way to do things), is 0.0005". That is only .5/1000" variation in roundness.

So I guess you could call it a little small, but reasonably round (that's what she said).

original.jpg
Click to expand...
Tricky with a dial caliper ... you need a spherometer.

www.si.edu

Spherometers | Smithsonian Institution

A spherometer is a device that does just as the name suggests: it measures (ometer) a sphere (sphere). But what exactly would you measure on a sphere?... Learn more
www.si.edu www.si.edu

Dave <-- has 2 spherometers, one antique like the ones shown in the Smithsonian article, and the other shop-made-by-Dave with a 0.0001" Starrett large-face dial indicator https://forums.azbilliards.com/thre...read-what-you-buy.526014/page-43#post-7250797
 
justnum said:
The idea of creating a perfectly round sphere is a topological problem.

In terms of producing the billiard ball more roundly the construction techniques would have to evolve.

Equally worth arguing is the roughness or smoothness of the surface area on the balls. The balls are coated with a smooth finish. If instead it had a slight texture, I think it would help roll over table impurities. Would it solve skids maybe some.

Each improvement should being a clear advantage to the game. Fixing skids and golden breaks may or may not be solved by Aramith.


Shamos and Jewetopologicaltt were the two names mentioned in Byrnes book. Byrnes book was my pool bible for more years than should have been.
Click to expand...
for the sanity of all of us, define, topological. unbelievable foolishness.
 
justnum said:
The balls are coated with a smooth finish. If instead it had a slight texture, I think it would help roll over table impurities. Would it solve skids maybe some.
Click to expand...
Exactly the opposite would happen, the texture of CB would interact with texture of OB can cause skids--just like the texture of chalk on the CB creates skid.
 
NASA created balls round to the atomic level for a space probe to determine frame dragging as the earth spins......... anything less perfect would create noise as the ball spins far greater than the effect NASA was trying to measure.

See Grace Satellite.
 
stunshotDAVE said:
for the sanity of all of us, define, topological. unbelievable foolishness.
Click to expand...

How would you make a ball with a limited amount of clay? Your not allowed to put holes or cut the clay.

Just press and shape.
 
MitchAlsup said:
Exactly the opposite would happen, the texture of CB would interact with texture of OB can cause skids--just like the texture of chalk on the CB creates skid.
Click to expand...

Not if the textures where perpendicular.

Here is an example.

1689114736171.png
 
In the 1989 BCA trade show, Rashig of Germany bested every ball manufacturer by staying within .002 off round on the spherical micrometer….most other sets jumped to .004 when crossing a number or stripe.
 
Wow! this is why I never made it out of high school algebra! I was too busy hanging around Jimmy and Dorothy Wise's pool room to paying attention to all this stuff back in those years!
 
pt109 said:
In the 1989 BCA trade show, Rashig of Germany bested every ball manufacturer by staying within .002 off round on the spherical micrometer….most other sets jumped to .004 when crossing a number or stripe.
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I'll bring mine in from the garage and test some Centennials and a few others ... 0.002 or 0.004 makes a big jump on the Starrett :)

justnum said:
Not if the textures where perpendicular.

Here is an example.

View attachment 707958
Click to expand...
... and mesh like a perfect gear ? ... irregularities are just that, irregular, they are not a special case as shown.

Dave
 
justnum said:
The balls are coated with a smooth finish. If instead it had a slight texture, I think it would help roll over table impurities. Would it solve skids maybe some.
Click to expand...
Most skids are caused by chalk or other foreign substances getting on either the balls or the cloth. The invention of a chalk substitute that made it impossible for the substance to adhere to the balls or cloth would make a difference. Not a geometry or topology problem but an engineering problem. Nonetheless, as long as human hands touch the balls, foreign substances will occasionally be in play and skids will sometimes result.
 
sjm said:
Most skids are caused by chalk or other foreign substances getting on either the balls or the cloth. The invention of a chalk substitute that made it impossible for the substance to adhere to the balls or cloth would make a difference. Not a geometry or topology problem but an engineering problem. Nonetheless, as long as human hands touch the balls, foreign substances will occasionally be in play and skids will sometimes result.
Click to expand...

That is a more affordable solution to the skid problem.
 
Two different things - smoothness and roundness. The earth would feel like sandpaper if it were the size of a pool ball.

A ball's surface smoothness is measured in microns.
 
L.S. Dennis said:
Apparently not as round as you think! Here's something Bob and Dr Dave might enjoy. The following is an excerpt for Mike Shamos's wonderful book entitled, 'Pool History, Strategies, and Legends.' In it he states:

"It is said that the earth is relatively smoother than a billiard ball. Here is what that means: A ball is permitted to vary by .005 inches out of a typical diameter of 2.25 inches, which is about 1 part in 500. The greatest depth in the ocean and the height of the tallest peak earth are both around 30,000 feet, which calculated with a diameter of 8,000 miles amounts to about 1 part in 750, much less significant than the variance on a billiard ball"!

Looks like Aramith is going to have to go back to the drawing board!
Click to expand...
Not so quick,,,,,,,, I have 2 sets of Brunswick Centennials and have measured both of them thoroughly with micrometers and there isn't more than .0003 difference in any diameter measurements across the 2 sets, which by the way, one set is less than 6 months old and the other is almost 30 years old. I bought both sets brand new.
 
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