Are rail sights in the correct place? Should the gutter line be 2:1 rather than the cushion nose?

iusedtoberich

iusedtoberich

AzB Silver Member
Silver Member
I was drawing a table for fun in CAD and came across a couple interesting things. The dimensions of the cushions and the diamonds came from the WPA site, which is a copy of the old BCA specs, complete with typos. The picture shows a bank/kick from the corner to the side. On the right half of the table, I'm using the gutter line, which is how the ball moves in real life (disregarding rail compression). On the left side of the picture I'm using the nose of the cushion. Both are perfect mirrors. The angles are different. On the right picture, which I believe is correct, the aim point is not even perfectly across the diamond.

I believe I saw something similar to this in Wining One Pocket where they had an accurate table diagram with the diamonds. I haven't read it in 25 years though, and don't have the book handy right now. I vaguely recall the author of the book was suggesting the rail diamonds should actually be on the cloth gutter line to be accurate, rather than on the wood rail.

I think this all stems from the actual playing area that the center of the ball can "touch" is not really 2:1. This would be the gutter line. The gutter line is not 2:1.

I don't really have a point here, I just found this interesting. Maybe the question would be if tables were invented today, should they have been made with the gutter line being 2:1, rather than the cushion nose?

SCR-20230923-pfxp-2.png




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@Bob Jewett @dr_dave
 
The rail sights (diamonds) are in the right place to give good compensation for a rolling ball without side spin on a one-rail kick/bank.

Carom system players are well acquainted with the difference between "through" and "opposite" use of the diamonds, so it would be perplexing to them if you started moving the sights.

The author of Winning One Pocket is Eddie Robin. He has one of the best treatments of use of the diamonds in that book. At the end he says that you better use your feeling/experience as well as the numbers.
 
The rail sights are offset for the purpose of allowing for the radius of the ball at the rail contact point for multiple rail solutions. With 1 rail bank I believe the adjacent point on the rail would be the better method.
 
I’m not so sure a purist wants to hear this….but at best the diamond system is ‘rule of thumb’.
If you made all the math perfect, you’d still have inconsistencies….age of the cloth, humidity…so on.
When I was a kid, I bet a guy $10 he couldn’t find me the measurements that would satisfy his ideal size..we had 8-9-10,and 12 foot tables…
…..he had to pay me.
The modern snooker balls have changed too, they’re now slightly bigger….from 2/16 to 2/15.
 
pt109 said:
I’m not so sure a purist wants to hear this….but at best the diamond system is ‘rule of thumb’.
If you made all the math perfect, you’d still have inconsistencies….age of the cloth, humidity…so on.
When I was a kid, I bet a guy $10 he couldn’t find me the measurements that would satisfy his ideal size..we had 8-9-10,and 12 foot tables…
…..he had to pay me.
The modern snooker balls have changed too, they’re now slightly bigger….from 2/16 to 2/15.
Click to expand...
When did snooker balls change, always been 2 1/16 in UK and 2 1/8 in USA as far as I ever knew.
 
Bob Jewett said:
The rail sights (diamonds) are in the right place to give good compensation for a rolling ball without side spin on a one-rail kick/bank.

Carom system players are well acquainted with the difference between "through" and "opposite" use of the diamonds, so it would be perplexing to them if you started moving the sights.

The author of Winning One Pocket is Eddie Robin. He has one of the best treatments of use of the diamonds in that book. At the end he says that you better use your feeling/experience as well as the numbers.
Click to expand...
Yes, Mr Robbin. I'll be back at the book next week and can review it.

I didn't mean to redo the rails today. I more meant: "if pool/carom tables were invented today, yet we magically knew everything about them, would it have been better to make the gutter line a true 2:1, and/or to move the sights on the cloth or somewhere else"?
 
Renegade_56 said:
When did snooker balls change, always been 2 1/16 in UK and 2 1/8 in USA as far as I ever knew.
Click to expand...
Found it out by accident maybe a year ago….they aren’t making a point of publicizing it.…..
….gotta a feeling it’s because they’ve been using the metric system for quite a while now.
 
iusedtoberich said:
Yes, Mr Robbin. I'll be back at the book next week and can review it.

I didn't mean to redo the rails today. I more meant: "if pool/carom tables were invented today, yet we magically knew everything about them, would it have been better to make the gutter line a true 2:1, and/or to move the sights on the cloth or somewhere else"?
Click to expand...
There are Many Carom table manufactures around the world that build 3C tables Now/today.
 
pt109 said:
Found it out by accident maybe a year ago….they aren’t making a point of publicizing it.…..
….gotta a feeling it’s because they’ve been using the metric system for quite a while now.
Click to expand...
Well, snooker equipment generally is very well protected, I'd challenge anyone to find actual dimension of snooker bends around the pockets as well, they'll sell them to you, but they won't show you dimensions. At least it was that way a few years back.

So what are the diameters of snooker balls being used now? When I look at retail sites I still see the diameters I stated.
 
Renegade_56 said:
Well, snooker equipment generally is very well protected, I'd challenge anyone to find actual dimension of snooker bends around the pockets as well, they'll sell them to you, but they won't show you dimensions. At least it was that way a few years back.

So what are the diameters of snooker balls being used now? When I look at retail sites I still see the diameters I stated.
Click to expand...
2-15
I‘d probably like it better….always liked the American size, even though I started playing snooker in Canada.
 
iusedtoberich said:
Maybe the question would be if tables were invented today, should they have been made with the gutter line being 2:1, rather than the cushion nose?
Click to expand...
I can't think of a reason to care about the 2:1 ratio, but it might be helpful for "measuring" banks/kicks to have the end diamonds aligned with the gutters rather than the cushion noses (and the spacing of the other diamonds adjusted accordingly).

pj
chgo
 
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pt109 said:
Sorry….2-1/15
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hmm,,,,,,,, you realize that is 52.5mm, and only .004" bigger than the standard 2 1/16. I'd bet that is just a marketing point and well within the diameter tolerance they've always used.

Not calling you out pardner, just trying to understand the difference.
 
pt109 said:
I’m not so sure a purist wants to hear this….but at best the diamond system is ‘rule of thumb’.
If you made all the math perfect, you’d still have inconsistencies….age of the cloth, humidity…so on.
When I was a kid, I bet a guy $10 he couldn’t find me the measurements that would satisfy his ideal size..we had 8-9-10,and 12 foot tables…
…..he had to pay me.
The modern snooker balls have changed too, they’re now slightly bigger….from 2/16 to 2/15.
Click to expand...
Well, yes, but they are not specified as 2 1/15 -- it's in mm. I wonder if someone got the conversion wrong when the changed over or if they put the metric size at the upper end of the allowed size for 2 1/16. The current spec is 52.5mm which is very close to 0.005" larger than 2 1/16. (0.005" is the current tolerance on pool balls but most are much more accurate than that.)

Edit ... Looking at the 1978 rule book which is the first with metric measurements, they give 52.5mm and call it 2 1/16. Perhaps someone on the rules committee was not so good with his sums. The tolerance both before and after the change was "within manufacturer's tolerance." The tolerance now is +- 0.05mm which is roughly 0.002 inches.

52.5mm = 2 1/16 + 0.07/16 measuring as 16ths
52.5mm = 2 1/15 + 0.004/15 measuring in 15ths

52.5mm = 2 + 17/254 inches exactly by the definition of the inch

So.... Your estimate of 2 1/15 was not correct either. ;)
 
Bob Jewett said:
Well, yes, but they are not specified as 2 1/15 -- it's in mm. I wonder if someone got the conversion wrong when the changed over or if they put the metric size at the upper end of the allowed size for 2 1/16. The current spec is 52.5mm which is very close to 0.005" larger than 2 1/16. (0.005" is the current tolerance on pool balls but most are much more accurate than that.)

Edit ... Looking at the 1978 rule book which is the first with metric measurements, they give 52.5mm and call it 2 1/16. Perhaps someone on the rules committee was not so good with his sums. The tolerance both before and after the change was "within manufacturer's tolerance." The tolerance now is +- 0.05mm which is roughly 0.002 inches.

52.5mm = 2 1/16 + 0.07/16 measuring as 16ths
52.5mm = 2 1/15 + 0.004/15 measuring in 15ths

52.5mm = 2 + 17/254 inches exactly by the definition of the inch

So.... Your estimate of 2 1/15 was not correct either. ;)
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Glad you took note, Bob….I had always meant to bring it up…..things just aren’t as tidy as they’re thought to be.
I knew a guy years ago who bet he played on a 7x14….turned out he’d played on a table that was 6x12 inside the rails…
….only one I ever heard of.
 
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So the impetus of drawing an accurate table in CAD was I wanted to make a 3-d printed ramp (like a stimp meter) to test rail rebound angles across different tables. The ramp would butt up against the cushion nose of two adjacent rails for consistency, at the corner pocket (or corner of a carom table). It would be pointed to the theoretical mirror line to make the ball kick/bank one rail into the side pocket.

However upon drawing the table in detail with the rail sights, the ball track lines, the gutter line, etc, I'm not so sure such an angle exists to make this ramp at a fixed angle that would be "geometrically" accurate across all table sizes. I think the ramp angle would actually have to change from let's say a 7' pool table to a 10' carom table. (I'm only talking about the perfect geometric mirror lines, not the real world effects of cushion compression, spin, etc). That's what led me down the path of is the table the ideal geometry.

Here are 2 more pictures. The first is a 100"x50" table. The second is a hypothetical 50"x25" table that makes the angle differences easier to see. See the 3 angles how they change? The only angle that stays the same between the two table sizes is the 53.13 deg, the one at the cushion nose, which is not real life because the ball can't follow that path. That angle does not change because the cushion nose is a true 2:1 length and width of the table. If instead, the gutter line were a true 2:1 length/width, then the path the ball actually took (the ball's centerline) would not change across table sizes.



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SCR-20230923-rhdw-2.png
 
iusedtoberich said:
So the impetus of drawing an accurate table in CAD was I wanted to make a 3-d printed ramp (like a stimp meter) to test rail rebound angles across different tables. The ramp would butt up against the cushion nose of two adjacent rails for consistency, at the corner pocket (or corner of a carom table). It would be pointed to the theoretical mirror line to make the ball kick/bank one rail into the side pocket.

However upon drawing the table in detail with the rail sights, the ball track lines, the gutter line, etc, I'm not so sure such an angle exists to make this ramp at a fixed angle that would be "geometrically" accurate across all table sizes. I think the ramp angle would actually have to change from let's say a 7' pool table to a 10' carom table. (I'm only talking about the perfect geometric mirror lines, not the real world effects of cushion compression, spin, etc). That's what led me down the path of is the table the ideal geometry.

Here are 2 more pictures. The first is a 100"x50" table. The second is a hypothetical 50"x25" table that makes the angle differences easier to see. See the 3 angles how they change? The only angle that stays the same between the two table sizes is the 53.13 deg, the one at the cushion nose, which is not real life because the ball can't follow that path. That angle does not change because the cushion nose is a true 2:1 length and width of the table. If instead, the gutter line were a true 2:1 length/width, then the path the ball actually took (the ball's centerline) would not change across table sizes.



View attachment 720428



View attachment 720429
Click to expand...
Well they HAVE to be slightly different because even though the ratio of the table is 2:1 for both, rail sites are spec'd from the inner rail and the same for both, as well as the fact that the ball sizes don't change in proportion to table size. They cannot possibly be the same if 2 of the 3 remain constant but the third does not.
 
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