Just for fun, How round is a billiard ball?

[MitchAlsup]

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.

If you watch a video on making ball bearings, you would see that there are a number of presses to get a cube of steel into s sort of round shape. Then the balls are dropped between 2 plates spinning in the opposite direction, and by the time the ball drops out of this it is considerably rounder. They typically do this 3 times and get bearings to better than 0.001" of roundness. Class 7 bearings go through another shot and are generally in the 0.000,2" range.

So, to make something round you mold it somewhat round, and then spin polish it until it is with spec.

 

[pt109]

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




Dave

David….if I recall correctly, Raschig prompted Aramith to get up to speed with the roundness thing.
In the 60s and 70s, some people knew you could give a slug rack with all the balls touching…rack them with numbers and stripes touching.

 

[tomatoshooter]

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.

I was thinking about that. A surface can be +/- 0.001" but have many variations, but another surface could have far greater total runout, yet this runout could be spread over a larger area.

 

[tomatoshooter]

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.

I can feel the numbers on a couple of my Aramith Premier balls. That must be why I missed that shot. I've seen pictures of an old Raschig nine ball set that had no numbers. Good thing they didn't change the colors on that set.

 

[AtLarge]

Here's a thread from long ago related to a billiard ball vs. the earth: https://forums.azbilliards.com/thre...-the-magnified-surface-of-a-pool-ball.283742/

A post by Bob Jewett on page 2 of that thread concludes: "Bottom line: New, polished pool balls are much rounder than the Earth and somewhat smoother than the "geologically interesting" areas of the Earth. Old, worn pool balls are still much rounder than the Earth but depending on damage may be rougher than the roughest spots on the surface of the Earth."

And here is the page on Dr. Dave's website about this subject: https://billiards.colostate.edu/faq/ball/smooth/

 

[Patrick Johnson]

...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.

Even better: if your decimal number is correct, it's actually 5/10,000 (5 ten thousandths), which is 1/10 of .005 (5 one thousandths).

pj
chgo

 

[3kushn]

If you watch a video on making ball bearings, you would see that there are a number of presses to get a cube of steel into s sort of round shape. Then the balls are dropped between 2 plates spinning in the opposite direction, and by the time the ball drops out of this it is considerably rounder. They typically do this 3 times and get bearings to better than 0.001" of roundness. Class 7 bearings go through another shot and are generally in the 0.000,2" range.

So, to make something round you mold it somewhat round, and then spin polish it until it is with spec.

I assume most folks don't know that the largest share of business for Saluc, who owns the Aramith Brand, is manufacturing Precision Ball Bearings.

This topic is sort of interesting to me and not to hijack ... Making a perfectly round object may be easier than making a peferct Cube... All sides are the same!!

 

[justnum]

I assume most folks don't know that the largest share of business for Saluc, who owns the Aramith Brand, is manufacturing Precision Ball Bearings.

This topic is sort of interesting to me and not to hijack ... Making a perfectly round object may be easier than making a peferct Cube... All sides are the same!!

Precision ball bearings are not designed to roll on a table, get smacked but rough chalk and frequently hit by other balls.

The pool problems that still exist today are skids, bad racks and foreign debris getting in on the action.

Emily tried to fix rack problems, changing colors means a different pigment. Metal based pigments carry more electrical charge and is more sensitive to static electricity
in the air. There are weak magnetic forces at play.

It could be worth suggesting that players are only allowed to chalk at their chair, not near or above table level altitude.

The idea of a round ball is a good problem.

 

[Banger]

Even better: if your decimal number is correct, it's actually 5/10,000 (5 ten thousandths), which is 1/10 of .005 (5 one thousandths).

pj
chgo

Yep. I spent about 10 minutes measuring the ball on numerous different axes, and the biggest variation I could find was about 1/2 of 1/1000". So from 2.2325" to 2.2330". Of course the dial caliper doesn't really measure to that level........it's just that the needle was between two marks.

BUT, as mentioned, I'm quite sure this is about the worst way possible to measure the roundness of a sphere, and the margin of error is great. My measurements could be off by....A LOT.

But it's OK, because it's all just for fun.

 

[3kushn]

Precision ball bearings are not designed to roll on a table, get smacked but rough chalk and frequently hit by other balls.

What are you saying??
Are you saying that Billiard balls don't need to be precision ball bearings? They just need to be able to be kicked around.
Precision Ball Bearings aren't only the size of a pea or smaller.
Makes no sense to me. What are you getting at.

Just for instance, and I don't know this Co more than 60 seconds. And maybe not the perfect example. I didn't get into their precision. Point is these folks make precision spheres 17" diameter!

Bal-tec was established in 1952 to custom produce precision balls that were not commercially available. We manufacture precision balls in any size from 0.005" ( 0.13 mm ) to over 17" ( 400 mm).

Bal-tec - Custom Precision Balls

 

[justnum]

What are you saying??
Are you saying that Billiard balls don't need to be precision ball bearings? They just need to be able to be kicked around.
Precision Ball Bearings aren't only the size of a pea or smaller.
Makes no sense to me. What are you getting at.

Just for instance, and I don't know this Co more than 60 seconds. And maybe not the perfect example. I didn't get into their precision. Point is these folks make precision spheres 17" diameter!

Bal-tec was established in 1952 to custom produce precision balls that were not commercially available. We manufacture precision balls in any size from 0.005" ( 0.13 mm ) to over 17" ( 400 mm).

Bal-tec - Custom Precision Balls

Tell the company to make balls designed so any chalk from the cue tip does not remain on the ball after contact.

Or design a cueball that does not need to be hit by a chalked cue stick.

 

[Rickhem]

Some interesting stuff here. It reminds me of all the hype about the mirror for the Hubble Space Telescope when that was first deployed:

"Laser tools were then used to polish the surfaces so that they would not deviate from the desired curve by more than 1/800,000th of an inch. To emphasize this precision, if Hubble's mirror were scaled up to the diameter of the earth, any leftover bumps on the glass would be no more than 6 inches high."

Full Article: http://www.scienceclarified.com/scitech/Telescopes/Hubble.html

After seeing the comparisons on billiard ball smoothness, what they did with the Hubble mirror is pretty incredible.

 

[BC21]

I was thinking about that. A surface can be +/- 0.001" but have many variations, but another surface could have far greater total runout, yet this runout could be spread over a larger area.

The +/- 0.001" is for roundness. The surface smoothness of a pool ball is closer to +/- 0.001mm.

An old beat-up cue ball might have a few nicks and dings in it, but still the overall/average smoothness is better than the Earth would be if we could shrink it down to the size of a pool ball.

I read somewhere, years ago, that a good spec for smoothness of a billiard ball is about 3 microns, which means any imperfections in the surface should be less than 0.003 millimeters. That's much smoother than Earth's surface.

What's interesting is that if the Earth could be shrunken down to a 2.25" sphere, it would feel like 600 grit sandpaper in some regions, 80 grit sandpaper in others, and probably about 220 grit over most of its surface. This takes in account the oceans and flat deserts and plains, compared to highest peaks and average mountains and valleys.

A pool ball, minus any obvious nicks/damage, is closer to 8000 grit sandpaper.

 

[iusedtoberich]

I was designing a sphericity measuring device last year. Have to get back on that project one day and finish it. See below single post, and expand the whole thread if you'd like more information.

Designing and building ball roundness tester

I'm working on a ball sphericity (roundness) tester for fun. Below are a couple of pictures, and a YouTube video link describing the process. I'll update as I go. My motivation is to see how different ball sets and brands compare both when new, and when worn. Also because I like making things...

forums.azbilliards.com

 

[hang-the-9]

for the sanity of all of us, define, topological. unbelievable foolishness.

Or "normal" for the poster

 

[Renegade_56]

Tell the company to make balls designed so any chalk from the cue tip does not remain on the ball after contact.

Or design a cueball that does not need to be hit by a chalked cue stick.

there is nothing, anywhere, that says you must use chalk

 

[justnum]

there is nothing, anywhere, that says you must use chalk

My cooking pan is nonstick.
Teflon is the material used to create that property.

I have a few other ideas to deal with the chalk pressed into the cueball during contact.

First I will debate all known materials. Teflon on a pool ball would it work?

 

[OldOrvis]

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!

but we all know the Earth is flat

 

[Cuedup]

but we all know the Earth is flat

Ha! You believe in flat?

You've been brainwashed. Flat doesn't exist. Nothing is flat upon close enough inspection.

 

[DaveK]

David….if I recall correctly, Raschig prompted Aramith to get up to speed with the roundness thing.
In the 60s and 70s, some people knew you could give a slug rack with all the balls touching…rack them with numbers and stripes touching.

Interesting. I tested my Centennial 1 ball and 15 ball, and found a maximum deviation of about 0.0015", certainly <0.002". The worst place was over the numbers and stripe as you noted .... on the other parts of the ball (1 ball in particular) the deviation was under a thou.

And my antique spherometer was useless for testing 2.25" balls, but may have had enough range to test Russian Billiards or perhaps bowling balls

Dave