Fractional aiming and required accuracy
- Thread starter Bob Jewett
- Start date
That's covered on Dr. Dave's website, somewhere. It depends on the condition of the balls and the speed of the shot. It's easy to do the test yourself with donuts. As I recall the test I did, which was the speed needed for a one pocket long-way bank, stun was 4 degrees and draw/follow were both 2 degrees for a half-ball cut. It's in one of my articles in Billiards Digest.
These two videos cover everything fairly well:
There are many intricacies involved with throw (and much of it is non-intuitive). If you want to get into the nitty-gritty details, see the list of effects and supporting resources here:
If you instead want a simplified version, see the "summary of the important things you need to know in your game about throw" at the bottom of the page here:
Enjoy,
Dave
First of all, sorry to resurrect a thread from 2020. However, I read through the replies, and while there were certainly some that explain what didn't seem clear to Chris, I wanted to add something, which might help others who see this discussion.
The fractions and resulting angles given are posited to be considered with the initial cue ball position *shifted laterally* (left or right). The (wrong) tendency is to imagine/view the fractions from an unmoving cue ball, where the aim line is pivoted through the cue ball center.
So, with compass references, a South-->North shot will be full (center/center). So, for a 1/2-ball aim, cutting target right, the cue ball shifts West, but the shot/cue line remains S-->N. If one instead pivots the aim line from the CB center, to the left (counter-clockwise), it will still be a 1/2-ball aim, but now the shot/cue line is more like South-Southeast-->North-Northwest. And of course, the final path of the target ball differs, because of the differing, initial cue ball positions.
Again, this is explained by Bob (and others, but I'm too lazy to look up names for credits), but I wanted to try and describe it differently.
[Final note: I think the CB position can also be moved along a curve--pivoted from the target--but the idea that the CB *moves* is what matters.]
That's right... A halfball aim will always produce a 30° cut angle (ignoring throw), whether the distance between cb and ob is 2 inches or 60 inches. Varying distance between cb and ob doesn't change that 30° angle. It simply shifts the angle away from center pocket.
If we set-up a center pocket halfball shot with 44 inches between cb and ob, then move the cb to only 10 inches from the ob (along the cb-ob centerline), and then aim a halfball from there, the 30° angle shifts, making the ob land too thick in relation to the pocket.
The change in perspective (measured in degrees) when moving the cb closer or farther from the ob is the amount of angle change needed to actually pocket the ball. In other words, using the example above, with 44 inches between the balls, our 30° cut hits center pocket, but at 10 inches we would need a 35° cut. The extra 5° is equal to the change in perspective as we move from 44 inches to 10 inches away from the ob.
5 degrees is quite a lot, but this change in perspective/angle isn't so extreme beyond a couple of feet between the balls. For example, the shot angle difference between a 44-inch distance and a 24-inch distance is only 1.2 degrees, and the difference between 60 inches and 24 inches is only 1.6 degrees.
How does the edge change?
As long as the center of the Cue ball is in line with the edge of the object ball doesn’t that always produce a half ball overlap?
It's like this: The halfball overlap is from two different cb-ob relationships, due to the difference in cb-ob distance. This applies only when the cb remains on the centerline between cb and ob. If the cb gets moved along the aim line (center cb to ob edge), then the angle doesn't shift or change at different distances, meaning the halfball aim will produce the same result from 2 inches as it will at 60 inches.
When referencing the center to center line from cb to ob, as Poolology requires, the cut angle shifts as the distance between cb and ob changes.
This diagram shows two different halfball aim lines, one red (closer cb) and one blue (farther cb). The red one is 8° from cb-ob centerline to ob edge, while the blue one is only 3°. The angle difference between these two shot perspectives is 5° (8 - 3 = 5). This means shooting a halfball shot from the closer cb will shift the 30° resulting angle by 5° compared to shooting the halfball shot from the farther cb.
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brian
your diagram helps explain it better
this is a 2 part answer/reply
i was thinking if you move the cue ball along the center to edge line
everything stays the same
my cue balls are not in the right places but if you put all the cue balls along the blue line which represents the line from the center of the farthest cue ball to the edge of the object ball
everything stays the same
yes?
BUT
if you put the cue balls on a line from center cue ball to center object ball (yellow line)
then as the cue ball gets closer the center to edge sends the object ball to a different place (in your example brian by 5 degrees)
red line blue line shows different angles
yes?
if you put the cue balls on a line from center cue ball to center object ball (yellow line)
then as the cue ball gets closer the center to edge sends the object ball to a different place (in your example brian by 5 degrees)
red line blue line shows different angles
yes?
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Yep, but it's really not much of an issue unless the cb is closer to the ob.
For example, using your diagram, the angle difference when shooting from the farthest cb, compared to the middle cb, is less than 1°. But the angle difference between your closest cb and farthest cb is over 4°.
Once the cb is a couple of feet or more from the ob, varying the distance is no longer an issue, because the angle/perspective difference isn't typically enough to cause a miss, which means the same fractional aim can be used to pocket the ball.
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It doesn't, as far as your *aim*. However, if the cue ball is moved forward or back on the cue ball center-to-center line to the target ball, then the actual contact point will change, and so will the resulting path of the target ball. This is what BC21 has shown.
To vary distance, with no change in the end result, the cue ball would need to be moved cue ball center-to-center of the ghost ball. This is what bbb has shown.
I congratulate this entire thread for being another reason to avoid teaching fraction aiming.
ba <- feeling sardonic
gvil
ba <- feeling sardonic
gvil