The tuning process is possibly the most confusing aspect of modern bowhunting. Even most experts don’t claim to have a foolproof tuning method that works all the time on all setups and shooting styles. Because there are so many variables in equipment and shooting styles, it’s difficult to write a foolproof laundry list for tuning. But some guidelines will solve most problems. Following is an overview of our procedures.
1. Check the poundage and draw length of your bow.
2. Determine the precise arrow length and point weight you will be using.
3. Consult the arrow manufacturer’s shaft selection chart to ensure that your shafts are properly spined to your bow.
4. Set the limb tiller. Even tiller to 1⁄8-inch less on the bottom limb is the accepted normal range.
5. Attach the arrow rest per instructions and adjust the rest in or out to line the arrow up with the centerline of the bow.
6. Attach the nock locator to the string. Level to 1⁄4-inch high is considered normal, but be sure to consider the diameter of your arrow shaft. If you shoot with a release aid and use nocking points on the string, use at least two nock sets to prevent slippage. Many archers these days use a string loop in place of nock sets. A string loop will not slide up the string.
7. Spray foot powder on the arrow rest and riser or on the shaft and fletching. Shoot an arrow and check for fletching contact. Remember that minor contact from the shaft is inevitable.
8. Fletching contact with the rest can often be reduced by turning the nock slightly in one direction or the other. For this reason it is best not to glue nocks onto new arrows until after you find whether this adjustment is necessary.
9. Shoot through paper from close range. Your arrow will be on its worst behavior at 7 to 10 yards from the bow. Try to achieve a bullet hole, but accept a slightly high-left or left tear (opposite for left-handed shooters). A tear of 1⁄2 to 3⁄4-inch, in addition to the shaft and fletching size, is acceptable at close range.
10. Bare-shaft tuning is another method of checking arrow flight. If you use this method, shoot your first arrow from very close range (3 to 4 yards). Poor arrow flight is exaggerated when there is no fletching attached. If you shoot from a greater distance and the arrow is not flying straight, the force of impact may bend the shaft when it strikes the target butt.
Tuning Overview Arrow Test
The Paper Tuning Arrow Test is the most commonly used bow tuning test for archers using compound bows with mechanical releases. This test also works well for finger release archers.
1. Firmly attach a sheet of paper to a frame approximately 24 in. x 24 in.
2. Position the center of the paper about shoulder height with a target mat about six feet behind the paper to stop the arrows.
3. Stand approximately four to six feet from the paper.
4. Shoot a fletched arrow through the center of the paper.
5. Observe how the paper is torn.
The tear in Diagram A indicates good arrow flight. The point and fletching enter the same hole. The tear in Diagram B indicates a low nocking point. To correct, raise the nocking point 1⁄16-inch at a time, and repeat the procedure until the low vertical tear is eliminated. The tear in Diagram C indicates a high nocking point or clearance problem for a finger release. To correct, lower the nocking point 1⁄16-inch at a time until the high tear is eliminated. If, after moving the nocking point a few times, the problem is unchanged, it most likely involves a lack of vane clearance. For a mechanical release, the tear in Diagram C indicates a high nocking point or a very weak arrow. To correct, move the nocking point as recommended for a finger release. Also try the following in order, ONE AT A TIME:
1. Reduce peak bow weight.
2. Use a lighter arrow point.
3. Use a stiffer arrow.
4. Check compound bow for proper timing (roll-over) of
the wheels or cams. The tear in Diagram D indicates a stiff arrow reaction for right-handed finger release archers. To correct, try the following in order, ONE AT A TIME:
1. Increase arrow weight
2. Use a heavier arrow point.
3.Weaken cushion plunger tension.
4. Use a weaker arrow.
5. For compound archers only, move rest slightly in toward the bow.
The tear in Diagram D is rare for right-handed mechanical release archers. However, it can happen, and often means the
arrow rest position is too far to the right or there is possible vane contact on the inside of the launder rest toward the bow. Mechanical release archers can try to move the arrow rest to the left to correct this problem. It can also indicate too much torque is being applied to the bow, possibly caused by the archer grabbing the bow or holding the grip too tightly. The tear in Diagram E indicates an arrow is too weak or has a vane clearance problem for fingers release archers. To correct, fingers shooters should try the following in order, ONE AT A TIME:
1. Check for vane clearance.
2. Decrease peak bow weight.
3. Use a lighter arrow.
4. Use a stiffer arrow.
5. Fingers shooters only: Move the arrow rest slightly out, away from the bow. For mechanical release, the left tear usually indicates a weak arrow and/or vane clearance problem. To correct, try the following in order, ONE AT A TIME:
1.Move the arrow rest to the right.
2. Check for bow hand torque. Don’t grab the bow.
3. Decrease peak bow weight.
4. Use a lighter arrow.
5. Use a stiffer arrow.
A diagonal tear (Diagram F shows one possibility) indicates a combination of more than one problem. First, correct the vertical
problem by adjusting the nocking point, as described above (Diagrams B and C). Then correct the horizontal disturbance with the instructions that apply to your shooting style. If you can’t eliminate the nocking point (vertical) problem, go to a pro shop and have your compound bow checked for proper “timing” (roll-over) of your eccentric wheels or cams, or have the tiller of your recurve bow checked. NOTE: These reactions and instructions are for right-handed archers shooting compound or recurve bows, except as notes. Lefthanded archers have opposite reactions and instructions.
*THE BEST WAY to find the minimum arrow weight for your bow/shooter combination is to follow the above AMO Recommended Minimum Arrow Weight. Chart released by the Archery Manufacturers and Merchants Organization’s Standards Committee. The chart was compiled through fatigue tests by some of the archery industry’s finest engineers. Follow the chart’s recommendations, and the result will be your fastest, safest, most durable setup.
1. Make only one adjustment at a time.
2. If you experience a high nock tear, lower the nock locator or use a weaker launcher arm or setting. For a low nock tear, do the opposite.
3. For right and left tears, change the center shot or adjust the spring tension in the cushion plunger.
4. When dealing with the arrow rest and nock locator, make the first adjustment a minor one. If that doesn’t provide the desired result, make the second adjustment more significant. If there is no change after a third adjustment, go back to your original setting and try something else.
5. Re-read the rest instructions carefully for helpful hints.
6. Some fingers shooters force an “S” curve in the string with their fingers. With no arrow on the string, draw the bow in front of a mirror or have a friend watch you draw, to identify string twist at full draw.
7. If you have severe string twist, consider dropping the top or bottom finger as you reach full draw. Some of the nation’s best tournament shooters use this method of shooting to improve accuracy.
8. On compound bows, adjust the poundage up and down to see whether either change effects positive results.
9. Release shooters should consider using an eliminator button or a string loop.
10.Consider using feather fletching. Feathers are more forgiving than vanes.
11. Experiment with shafts of different spine values.
Be aware that a low brace height, short axle-to-axle length, radical cams, overdraws, and high arrow speeds can all make a bow more difficult to tune. Also, improper hand position on the grip can torque the bow and affect “tune.” The bow hand must remain relaxed, and hand placement must be consistent. Other trouble-shooting ideas include a check of wheel synchronization and limb deflection. Checking for these conditions usually requires the assistance of a skilled bow technician. Some pro
shops offer this service at a competent level. (Of course, with modern single-cam bows cam synchronization is no longer a concern.)
When your arrows cut perfect holes through paper at all distances beyond 15 to 20 yards, it is time to move on to the important but often overlooked portion of the bow tuning equation: the accuracy test. But, remember, an accuracy test has meaning only in relation to your ability as a shooter. Your shooting skills must be good enough to notice subtle changes in your bow’s accuracy.
You often can create tighter groups by making minor adjustments to the following:
1. Nocking point location
2. Center shot adjustment
3. Cushion plunger tension
Again, I feel accuracy and arrow flight are the bottom line. As long as you have both, the tuning method used is not important. Some of us get so hung up on tuning that we fail to follow up with an accuracy check — even though accuracy is the cornerstone to success.
4. Rest launcher tension
THE BALANCE POINT of an arrow is the exact point along the shaft at which it will balance when laid horizontally on a narrow object. As the arrow’s balance point is moved forward of its physical center, the fletchings gain an increased leverage advantage and thus have better control over the flight of an arrow. This is particularly significant with hunting arrows, because broadhead blades compete with the fletching for control of the arrow. Determining the proper forward of center (FOC) balance point is not an exact science, because arrow flight depends on the size of the fletching, the size of the broadhead, the length of the shaft, and how smoothly the arrow is launched. We simply want an adequate FOC balance point to ensure that our arrows are not approaching an unstable condition. A 10-percent FOC balance point will, in most cases, provide stable arrow flight. Less may or may not provide adequate control. A more forward balance point, say up to 20 percent FOC, is generally not necessary, but it should not cause a problem. Do remember, however, that weight added to the front of an arrow does weaken its dynamic spine.
Three primary factors combine to affect balance point:
1) The weight of the components attached to the rear of the arrow.
2) The weight of the components attached to the front of the arrow.
3) The length and weight of the shaft.
To move the balance point forward, you can remove weight from the rear, add weight to the front, or do both. Most finished arrows have an acceptable balance point, but it is a good idea to check. If the balance point is too far aft (toward the fletching), you may experience arrow flight problems. Short arrows fletched with large plastic vanes (vanes are heavier than feathers) and lightweight broadheads are the most likely to have questionable balance points. As always, arrow accuracy should be the determining factor. To find the balance point of an arrow, place it on a narrow object. Your finger will suffice, but something with less surface area, like the back of a knife blade, will work better. Place the completed arrow (target point or broadhead installed) on the narrow edge and move it back and forth.
When you find a point at which the arrow does not tip in either direction, precisely mark that spot – that’s the balance point. Next, measure your arrow from the bottom of the nock slot to the back of the insert, and record the number. This measurement is often referred to as the “cut length.” For carbon arrows with an outsert point adapter, measure from the bottom of the nock slot to the back of the outsert and add 3⁄4 of an inch. In both cases this gives you the total shaft length. If you make all measurements in 10ths of an inch they will be easier to calculate. Now, divide the shaft length number by two and place a second mark in the exact center of the shaft (between the two measuring points.) Thus, if the cut length of your arrow is 30 inches, the center of the arrow will be 15 inches from each end. The balance-point mark should be closer to the front (point end) of the arrow, the center-point mark closer to the nock end. (The specific points at which shafts are to be measured and the calculations used to determine the balance point of an arrow are set by an ASTM standard. The designation number is F1435-94.) To determine whether your arrow is properly balanced, measure between the two marks you placed on the shaft. This is the distance between the center of the shaft and the balance point. Now divide that number by the cut length of the shaft (the large into the small). The resulting number is the FOC balance point. Example: Let’s say the distance between the center mark and the balance-point mark is 3 inches, and the cut length is 30 inches. Divide 3 inches by 30 inches, and you get 0.1000. Now move the decimal point two places to the right and you have the FOC balance point expressed as a percent (10 percent in this case). Or you can multiply 0.1000 x 100 and the decimal point will move automatically, producing the same results. WITH ALL WE know about penetration today, we're completely comfortable with saying that, all else being equal, the power an arrow possesses– its ability to penetrate a target – is a function of kinetic energy.
Kinetic energy is a function of arrow weight and velocity combined. (Of course, when addressing kinetic energy we’re assuming that arrows are striking in the same place, and in the right place. Proper arrow placement is critical.) To calculate kinetic energy, measure arrow speed one yard from the bow. Once you know arrow speed and arrow weight, apply the following formula: Arrow speed times arrow speed; times arrow weight; divided by 450,240, equals kinetic energy in foot-pounds. Example: 240 fps x 240 fps = 57,600.00 x 500 grains = 28,800,000 divided by 450,240 = 63.965 foot-pounds of kinetic energy.