How do you aim combination shots when the gap between the balls is small?

The following videos explore throw effects related to small-gap combinations with various gap sizes between the balls:

For more info, see “Small-Gap Combos” (BD, August, 2018).

Here are some useful conclusions from a math/physics analysis in TP B.21:

  • When the gap between the OBs is 3/8″ (9.5mm) or 1/6 a ball diameter or 1/3 a ball radius, the 2nd ball heads very straight (i.e., the throw effect cancels the cut effect) over a fairly wide range of 1st-ball angles, regardless of ball conditions. At larger angles, the 2nd ball heads in the cut direction (because the cut effect is larger than the throw effect). Fortunately, 9.5mm is just slightly smaller than the diameter of typical low-CB-deflections shafts, so it is easy to judge the optimal gap size with your tip. Alternatively, you can visualize the gap size as 1/3 the radius of a ball (1/3 * 1.125″ = 1/3 * 9/8″ = 3/8″). Alternatively, visualize 3/8″ as between 1/4″ and 1/2″ (which many people can picture fairly easily).
  • When the gap between the OBs is very small (much less than 3/8″ or 9.5 mm), the 2nd OB heads in the throw direction at smaller 1st-ball angles and slower speeds (except at really small angles where speed has no effect), but the 2nd OB heads in the cut direction at larger angles and faster speed. The largest throw effect occurs close to a 1/2-ball hit.
  • When the gap between the OBs is larger than 3/8″, the 2nd OB always heads in the cut direction, regardless of shot speed; although, throw reduces the cut more at slower speed (except at small angles where the speed has no effect).
  • When the gap between the OBs is 1/4″ (6 mm), a fast speed shot results in less accuracy for small angles (less than about 15°), but the accuracy is within +/- 1 degree over a larger range of 1st-ball angles. For 1st-ball angles below about 20°, the error is in the throw direction, and for angle above about 20°, the error is in the cut direction.
  • If a small-gap combo is wired to the center of a pocket, with a gap size between 1/4″ (6 mm, about 1/2 the width of a typical shaft) and 1/2″ (13 mm, about the width of a typical shaft), anything fuller than a 3/4-ball hit between the 1st and 2nd OB will result in pocketing the 2nd ball (at any speed) for average distances and pocket sizes.

When there is no gap between the balls, the 2nd ball throws the most (but not much more than when there is a very small gap). For more info and demonstrations, see the frozen-ball throw resource page.

The info above also applies to cut shots where the CB is close to the OB and hit with stun. The difference is you have direct control over the CB’s spin. With small-gap cuts, sidespin can be used to change the throw amount and/or direction, and top/bottom spin will reduce the amount of throw (see throw draw/follow effects).

Here’s an interesting example of a straight small-gap or frozen combination, where the 1st ball needs to be sent forward:

Can you use sidespin instead of CIT to throw a small-gap or frozen combo?

Yes, but it is much easier to judge and control combo throw with cut-induced throw (CIT). Although, sidespin is sometimes useful to eliminate cut-induced-spin effects, per the demo and explanation here:

If CB control is a issue, using sidespin to throw the combo might be a good alternative to cutting the 1st ball. CB sidespin (ex: right) throws the first ball (ex: left). If there is a gap, this cuts the 2nd ball (ex: right). The transferred spin on the 1st ball (ex: left) would also tend to throw the 2nd ball (ex: right), but the CIT direction between the 1st and 2nd balls is in the opposite direction, so the effects combine in complicated ways. For more info, see the answers to questions about throw.

Again, it is easier to judge combo throw by using CIT and gearing spin.

Does the 3/8″ value change with ball conditions?

No. The 3/8″ value applies to all conditions, even with a chalk mark at the contact point, because the rule applies only over a small range of combo cut angles, where the OBs are gearing together during contact (with no sliding between the balls when they separate). Having extra friction does not change this situation. Now, for bigger cut angles, a chalk mark at the contact point can have a huge effect on shot outcome, per the demonstration on the cling/skid/kick resource page.

For more information, including the math and physics details, see TP B.21.

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