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- Thread starter MDSPHOTO
- Start date

I would love to see a diagram of this semi circle of death, to use for instructional purposes. Anyone know where I might find one? - thanksThe Semi-Circle of Death is the half circle drawn from corner pocket to corner pocket passing through the spot. Straight lines to both corner pockets from any point on that semi-circle form a 90-degree angle. That means pocketing an OB that's on that semi-circle (including a ball on the spot) into either corner pocket with a stun hit (so the CB caroms straight along the 90-degree "tangent line") will scratch the CB in the other corner pocket.

pj

chgo

The first drawing shows the Semicircle of Death (dashed line) for the shot posted above. The solid lines are examples showing the right angles formed at various places on the semicircle connected to both pockets.I would love to see a diagram of this semi circle of death, to use for instructional purposes. Anyone know where I might find one? - thanks

The second drawing shows more Semicircles of Death in several places on the table - wherever a semicircle can connect two pockets.

pj

chgo

Last edited:

Thanks! In the OP‘s original diagram, the 8-ball appeared to be located a few inches below the foot spot, which is even more reason it would be easy to avoid the scratch.The first drawing shows the Semicircle of Death (dashed line) for the shot posted above. The solid lines are examples showing the right angles formed at various places on the semicircle connected to both pockets.

The second drawing shows more Semicircles of Death in several places on the table - wherever a semicircle can connect two pockets.

pj

chgo

View attachment 601597

View attachment 601598

Quit shooting so hard. Otherwise you will scratch every time. Roll the CB and cut the 8 in.I can make this shot 8 out of 10 times, unfortunately I scratch about the same amount of times. How do I not pocked the cue ball on this shot? View attachment 601336

Scott Lee

Are there any resources that explain how this is put to use?The first drawing shows the Semicircle of Death (dashed line) for the shot posted above. The solid lines are examples showing the right angles formed at various places on the semicircle connected to both pockets.

The second drawing shows more Semicircles of Death in several places on the table - wherever a semicircle can connect two pockets.

pj

chgo

View attachment 601597

View attachment 601598

If you know what a tangent line is and how to use it to predict/control the direction the CB goes after contact, then you know all there is to know about it. As usual, I recommend Dr. Dave's info on it: https://billiards.colostate.edu/faq/stun/90-degree-rule/Are there any resources that explain how this is put to use?

pj

chgo

I have a good understanding of the tangent line and using it to predict cue ball direction. Execution is another matter. Just wondering if the circles had some practical application.If you know what a tangent line is and how to use it to predict/control the direction the CB goes after contact, then you know all there is to know about it. As usual, I recommend Dr. Dave's info on it: https://billiards.colostate.edu/faq/stun/90-degree-rule/

pj

chgo

For what it's worth, I can scratch from just about anywhere on the table!

None that I know of, other than being able to predict the scratch - but if you know your tangent line stuff you already know that for every shot, including the ones on these lines.Just wondering if the circles had some practical application.

pj

chgo

See my columns from 2007 here: http://www.sfbilliards.com/articles/BD_articles.htmlAre there any resources that explain how this is put to use?

There are two columns about the semicircle.

"The Poisoned Point of Double Death"? lolSee my columns from 2007 here: http://www.sfbilliards.com/articles/BD_articles.html

There are two columns about the semicircle.

By the way, I think they mistakenly substituted pictures of your son (good looking kid).

pj

chgo

The Semi-Circle of Death is the half circle drawn from corner pocket to corner pocket passing through the spot. Straight lines to both corner pockets from any point on that semi-circle form a 90-degree angle. That means pocketing an OB that's on that semi-circle (including a ball on the spot) into either corner pocket with a stun hit (so the CB caroms straight along the 90-degree "tangent line") will scratch the CB in the other corner pocket.

pj

chgo

Dollar bill is an easy and handy rule to check the tangent line, as it has 90 degree angles.

I think one of the most important skills for a player to acquire to get past "OK intermediate" level is to learn to judge tangents and right angles by eye. And I know at least one "pro" player who would call a foul if you got a "measuring device" out of your wallet.Dollar bill is an easy and handy rule to check the tangent line, as it has 90 degree angles.

Your cue stick is the only thing that by the rules you are allowed to use as a measuring / alignment device, as long as you don’t let loose of it.My goodness, how could any functioning adult not know what a 90 degree angle looks like? And I see players (even pros) using measuring devices all the time....they use their cue stick to determine angles off the rail, particularly on bank shots.

Many people escape from school rather than graduate from it. I know an instructor who felt it necessary to build a right angle from PVC pipe so his students could see a right angle.My goodness, how could any functioning adult not know what a 90 degree angle looks like? ...

If a shot is aligned with the sides of the table (NSEW), most people will get the "right" answer. If the shot is 24 degrees off axis, the perpendicular for a large fraction of students ends up in very strange places. This is a large problem when learning to play position.

future cue sticks will have mininprocessors that can use an AI to hypothesize percentages for each shot.My goodness, how could any functioning adult not know what a 90 degree angle looks like? And I see players (even pros) using measuring devices all the time....they use their cue stick to determine angles off the rail, particularly on bank shots.

I can post a demo in a few months.

Well, it's OK with me. They can use a dollar bill, as far as I'm concerned, as long as they do it in a timely manor.Your cue stick is the only thing that by the rules you are allowed to use as a measuring / alignment device, as long as you don’t let loose of it.

I can post a demo in a few months.

You can't escape from the world. 90 degree angles are everywhere. We grow up looking at 90 degree angles. A piece of paper, the corner of a book, a computer screen, cell phones, the doors in most houses, the wall in most houses, a dollar bill. All have 90 degree angles on the corners.Many people escape from school rather than graduate from it.

It must be mighty discouraging at times, to be an instructor.I know an instructor who felt it necessary to build a right angle from PVC pipe so his students could see a right angle.