Tuning the Barebow

This is another extract from “EQUIPMENT MODULE – BARE BOW – FITA LEVEL 2 MANUAL”. It is authored by Tom Bil, Former Netherlands National Team Coach for Field and Disabled; and Former National Coach for Austria. FITA is now known as World Archery. Click on the hyperlink to find out more about this organisation. The contents of this page have been replicated in its entirety and WITHOUT  editing. It is very useful reference on the fundamentals of bow tuning, invaluable in the quest towards the perfectly tuned bow.

TUNING THE (BARE) BOW:
Principles of tuning:
All archers are from time to time forced to tune up their bow setup.
Bow and arrows are bought independently from each other, the bow just according to a recommended draw weight and the arrows according to a more or less rough estimate in the selection chart. They shall fit to any archer and are not at all tuned up, not even to a certain degree. Tuning is not especially concerning the bare bow but also to every other bow in order to achieve high scores.
Provided the archer has a perfect form; what determines where the arrow hits the target are the initial arrow flight properties (direction of travel, speed, archers paradox, release.) and the physical properties of the arrow (mass, length stiffness = spine) If we replace the archer with a shooting machine which handles the bow/arrow system exactly the same way on each shot and the bow/arrow system responds exactly the same way on each shot then the initial arrow flight properties would be exactly the same on each shot. If all the arrows had exactly the same physical properties then every arrow would hit in exactly the same spot. In this case there would be no benefit to be gained from bow tuning. You adjust the shooting machine so the bow is pointing in the right direction to hit the target centre and then you get a perfect score.
Archers are not shooting machines (though some seem to get pretty close to it and isn’t that what we’re striving for). The way the archer operates the bow each time will in some way be slightly different. As a consequence the operation of the bow/arrow system will be slightly different. The resulting initial arrow flight characteristics will be slightly different and as a result where the arrow hits will be slightly different. The minimum arrow spread (group size) is obtained when the arrows leave the bow with zero offset angle ( the angle caused through the off centre position) and no rotation. The purpose of basic bow tuning is to get such a setup so that the archer’s shot meet these criteria.
The fact that tuning relates to the archer’s average in form and varies from shot to shot means that a statistical approach has to be applied to any tuning system. If the archer shoots one arrow through sheet of paper and it happens to be a perfect hole then this is, by far, not enough for getting high scores..
A tuning approach either has to be based on looking at the same time at a lot of shot arrows or if the approach practically can only use a few arrows at a time, e.g. bare shaft tuning, it needs to be repeated lots of times and a composite picture built up. Proper tuning means that a lot of arrows have to be shot under the same conditions what weather but also the archer is concerned.

When an arrow is shot we have to deal with archers paradox, for the archers typical arrow it takes about 15-20 meters for the arrow to stabilize.(they talk about 5meters when an X10 or an ACE is shot). At longer distances this doesn’t matter but if you are shooting the short distances it will be of great influence.
The optimum tuning set up for short distances may be found to be different from the optimum tuning set up at longer distances.
Tuning the bare bow:
Tune the bare bow like the recurve bow (with aluminium or carbon arrow) with the exception of the following:
Tuning for string walkers is a compromise, as moving archers fingers up and down the string alters the ratio of the length of the top and bottom parts of the string from finger to limb nocks. In this the tillering is compromised but mostly they are reasonably forgiven in this respect. Keep the tillering as small as possible . (See limb adjustments and Nocking point)
How to get this compromise tuning of the Nocking point height?
By averaging the tuning at average halfway of the shortest (15mtr) and over halfway of the longest distance (30mtr)
Nocking Point
Nocking point is about +/- 4mm more than the tiller height depending on the kind of bow some bows need up to about 15 to 19mm above tiller height to the right angle of the arrow rest. (normally we talk about top and bottom tiller which is the distance between the string and the top or bottom limb pocket; the tiller difference recommended from the manufacturer, let’s say about 6mm in favour of the top tiller; the tiller height is 6mm + approximately 4mm = 10mm)
6mm Tiller
This would be a nocking point height for a recurve bow with sight at 6 mm tiller height.
10mm Tiller
This would be a nocking point as the above set example for bare bow 6mm + 4 mm= 10mm
16mm Tiller
And, believe it or not, there is a bare bow of a particular manufacturer where the nocking point extends up to 6mm + 4 to 13mm till 19mm.
Nocking points need consideration, especially if archers use the brass clamp on type. When the arrow is shot from between the index and second finger (Mediterranean), the string stays more or less at right angles (assuming there is a half-way 50% finger position) to the shaft.
When shooting three or two fingers under, at full draw, the string passes through the arrow nock at an angle. This means the nock sets have to be further apart to avoid pinching the arrow nock. The easiest way to see if the nock sets is in the right place look at the archer at full draw; if the string nock sets are to close together it causes to “pinch” the arrow, too far apart causes the arrow sliding up and down.
The Ambo nocks compensate for that as a brass/plastic ball is threaded into the string, (archer needs to be sure of the right place) provided the arrow nocks are shaped to fit the ball. The seat of the nock on this nocking point will not change by altering the brace height only if the archer alters the tillering.
Set the correct Nocking point height. If the Nocking point is incorrect then the arrow will “porpoise”, i.e. the point and tail of the arrow will oscillate in a vertical plane, there will be up- and- down oscillation of the arrow. (See Nocking point Bare bow)
The best way the nocking point can be checked for bare bow is with the Bare-shaft test.
The theory behind bare-shaft tuning is that a bare shaft will continue on in the direction it was shot since there are no fletchings to stabilise it.
Shoot at least three fletched shafts and two identically aimed unfletched shafts at a target at a distance of 15 and 30 meters. (the 15 meters will cover the short distances whereas the 30 meters being the half of the longest distance for Bare bow in the field) Of importance is that you as coach see to it that the archers shoots identical shots especially with the same finger position on string and face.
If the unfletched shafts impact above the fletched shafts, the nocking point is too low., if the unfletched shafts impact below the fletched shafts, the nocking point is too high (it is sometimes desirable to have the bare shaft impact just slightly below the fletched shafts to ensure that the nocking point is not too low as this could cause clearance problems. It also recommended to have the bare shaft slightly to the left (to compensate for the string reflex)?

Fletched and Bareshaft
Brace height
The manufacturers give a certain range for the brace height.
An experienced archer may adjust his/her brace height to compensate for individual shooting style, in the end it depends on the arrow flight (depending on the smoothness of the archers’ release skills) where the brace height ends up.
Get the bracing height right for the bare bow -Listen to the shot – does it sound nice? Does it sound harsh? Set the archers bow at minimum bracing height and increase it steadily to maximum and listen to the bow as it is shot. Do this with different finger positions on the string (String walking) until you think it sounds good.

Another way of sorting out the individual brace height is described in Rick McKinney’s book “The simple art of winning” is a another option.
Limb alignment
Limb alignment is a mechanism used to compensate for slight twists in the riser.
Traditionally, take-down recurve bow limbs sit in a limb pocket and lock into place. Limb alignment adjustment provides the facility to adjust the pocket/limb relationship. This can cause problems when the limb adjustment is of poor design, resulting in an unreliable bow. If possible, avoid limb alignment pockets and simply insist on a riser which is perfectly straight.
In order to determine if the limbs are correctly aligned, fit a long-rod to the bow, rest the bow
over the back of a chair or similar, ensuring that there is no weight or pressure on the limbs,
and stand back from the bow, looking with one eye.
(the long rod is fitted to the bow as a recurve bow so that when archer is alone he can align his bow from a distance, sometimes you see things better at a distance, when assistance is present the long rod is not needed)
The string should align as shown:

String alignment
Limb weight adjustment
In order to provide some flexibility, most modern risers provide the facility to adjust the draw
weight by tilting the point at which the limbs sit in the limb pockets. On some bows, this means adding packers to the bottom of the limb pockets to reduce the weight, on others the limbs are adjusted by means of an adjustment screw at the back of the limb pocket. In most cases this will only provide up to 4lbs (up to 10%) of adjustment.
Use a strong arrow rest. The arrow rest the archer wants to use has to be reliable firm when the archer string walks. Shooting with a gap of two inches and more between fingers and arrow creates a lot of down force on the rest. (See arrow rest, bare bow and its accessories)
To determine the right balance on the archers bare bow, so that after the shot the bow is stabile or the upper Limb might even move towards archer (instead away from archer towards the target) it is advised that firstly the archer apply with tape some lead (as used in fishing) on the lower part on the backside of the bow handle and note the amount of lead attached. (Grains). Now shoot some arrows at different distances and watch the performance of the bow..
The archers grip and its influence on the stability is described thoroughly in the Entry level Manual and should be considered.

By adding or decreasing the weight of lead the archer can now determine the amount of weight needed to stabilise the bow.

  • End of Article Extract
  • As a follow-on the archer can also get many useful points from Rick Stonebraker’s  Tuning for Tens”
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