How is cue deflection related to cue ball squirt?

“CB deflection,” as the term is commonly used, refers to the squirt of the CB away from its intended or expected path (assuming no squirt). The term “deflection” is also sometimes commonly used for the net effect of squirt and swerve (AKA squerve), referring to the deflected position of the CB (from the expected shot line) at the OB contact point.

The term “deflection” can be confusing and misleading. Here’s a good summary explaining why:

low-deflection” (LD) shaft =
“low-cue-ball-deflection” shaft =
“low-squirt” shaft =
“low end-mass” shaft =
usually flexible (AKA “whippy”, compliant, not stiff, “like a wet noodle”) shaft end with higher deflection (flex) (although, this is less the case with carbon-fiber LD shafts)

If you reduce the endmass of a shaft to create an LD shaft (e.g., by drilling out the end to make it hollow, or by turning down the shaft diameter close to the tip), the end of the shaft will also become less stiff (i.e., more whippy) close to the tip. This would cause the shaft to bend or flex (i.e., “deflect”) away more as a result of an off-center hit, while the low endmass would result in less squirt (CB “deflection”). This is why the term “deflection” can be misleading. A “low-deflection” wood shaft actually typically deflects (flexes) more as it creates less CB deflection (squirt). That’s why the term “squirt” (or “cue ball deflection”) is much clearer than just “deflection.”

Now, it is possible for an LD shaft to be light on the end (i.e., low endmass and squirt) and still be stiff (depending on the geometry and material used, maybe carbon fiber). Endmass is what determines the amount of squirt, and stiffness is what determines how much the shaft flexes and vibrates. As is clear in the the slow-motion videos on the shaft flex and vibration page, the shaft flexes and vibrates mostly after impact (after the CB leaves the tip), due to the momentum imparted to the endmass during tip contact. The flex and vibration mostly occurs after the CB is gone, and it has nothing to do with squirt (CB deflection). But it is probably best to ignore what the cue or shaft is doing (especially after impact, where most of the shaft flex and vibration occur). Cue flex and vibration depends on the stiffness of the shaft. Squirt (CB deflection) depends on the endmass of the shaft. More “endmass” causes the CB to squirt more. Less “endmass” causes the CB to squirt less.

Shaft stiffness has an indirect effect on shaft “endmass” (per the explanations on the endmass and stiffness resource page), but shaft stiffness is not as big of a direct factor on squirt as some people might think, as shown by the analysis in TP B.19 – Comparison of cue ball deflection (squirt) “endmass” and stiffness effects. Per the experiment in Diagram 4 of “Squirt – Part VII: cue test machine results” (BD, February, 2008), if mass is added to the end of a shaft, without changing the shaft stiffness, squirt (CB deflection) will be increased. And if mass is removed squirt (CB deflection) will be decreased.

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