Month: February 2019

So you have a new bow, followed advice on choosing arrows, and now want to set it up. There is a sequence of actions for doing this, which I will briefly outline here. This is as described by Simon Needham’s book: Archey, the art of repetition.

One thing that I would mention at this point is that the later parts of this sequence involves shooting groups of arrows and correcting the setup according to where that group is. Of course, the better your form, the smaller the group, and the more precisely you can use this to set up and tune the bow.

First assemble the bow, putting on limbs, button, sights, and stabilizers (the following is angled towards Olympic recurves).

Static set-up

Find true centre of the bow

The idea is to find the true centre of the bow and align everything with it. Rest the riser on the back of a chair (side rods help here, otherwise you will need somebody else to hold the bow vertical). Hold an arrow against the riser a bit above the arrow rest, and looking from above check if the arrow is parallel with the long rod. If they are parallel, then the long rod bushings are straight and the centre of the long rod is the bow’s true centre. If it is not, put a card with a hole in it on the end of the long rod (held in place by the weight), and mark on the card where the true centre is.

Align the limbs with the centre

This is best done with Beiter limb gauges attached to the limbs, although it is possible to manage without. In that case align the string with the hole that the limb bolts pass through.

Looking at the bow from behind, while it is on the chair back, check whether the string, when centred on the limbs, also aligns with the true centre. If not, use the lateral adjustments on each limb pocket to align the limbs both with the centre and with each other. First, move the lateral adjustment bolts so that the string passes through the centre of each Beiter gauge, both top and bottom. Now the limbs are aligned with each other. Next, sight down the middle of the string to the end of the long rod, and see that it is also aligned with the true centre. If not, you move the alignment bolts of both top and bottom limbs in parallel until it is.

Setting the tiller

Through an unfortunate defect in evolution, our hands do not have a nice handy hole in the middle for the arrow to pass through. Therefore, we hold the riser below the point where the string is pulled back; and consequently, the distance from the hand to the top limb tip is further than the distance from the hand to the bottom limb tip. Effectively this means that the bottom limb is bent more than the top limb, and the two limbs do not reach the resting point at the same time when the arrow is released.

To remedy this we wind out one limb more than the other. This is known as ’tiller’. This is measured with a bracing height gauge on each limb just at the point where it goes into the limb pocket. In general, bows shoot well when the top is 4-6mm more than the bottom

Set the arrow rest

Assuming this is a new bow, then you will need to put on the arrow rest at this point. Most of them are stick on, but some, such as the Spigarelli, bolt on. Before fixing it in place, put an arrow of the type you intend to use onto it and align it so that the button will touch the centre of the arrow and there is a little upward tilt of the arm that supports the arrow.

Set up the sight

The sight needs to be adjusted in a couple of ways. First, you adjust the sight pin, and then check that the sight rail is parallel to the bow, and if not adjust that.

With the bow still on the back of the chair, with one eye closed, check that the string is aligned with the Beiter gauges (or limb bolt if you don’t have those), and then without moving your head look down until you can see the sight pin aperture. The string should align up just to one side of the aperture, where the sight pin is attached to it. If it is not aligned, adjust the windage on the sight pin. As the same suggests, this side-to-side adjustment is not to put arrows on the target but to adjust for side winds when shooting outdoors. Without any wind, the whole bow should be in alignment around its centre, including the sight pin.

Next, check that the sight rail is parallel to the bow. Move the sight pin to the top of the rail, and check it is in the correct alignment. Then move it to the bottom of the rail and recheck. If the rail is parallel it will be in alignment at all points. Otherwise, there are normally two screws that attach the rail to the bar that goes back to the sight mount on the riser. These can be loosened and the rail rotated a few degrees to either side.

Set the nocking point

The nocking point height is critical, but can only be determined when we start shooting. At this point set it so that the bottom of the arrow is approximately 5mm above the arrow rest, using the bracing height gauge. If you are using Beiter nocking points it is best not to fit them at this point but to put on temporary nocking points.

Centre shot

Nocking point height and centre shot are critical. If these are wrong there isn’t much point messing about with other adjustments. While nocking point height needs to be determined accurately when we start shooting, centre shot can be determined in advance. With the bow still on the back of the chair, put an arrow on the string and sight from behind aligning the string with the Beiter gauges or limb bolt openings as before. Without moving your head, and with one eye closed, look to the tip of the arrow. For aluminium arrows, the string should be aligned with the edge of the arrow nearest the riser at its tip. For aluminium-composite and carbon arrows it is usually more central, ie with the string close to the center of the tip.

This is adjusted by loosening the collar around the button and adjusting it, so that the button sticks out to a greater or lesser extent from the riser. Note this is button position, not button spring pressure, which is adjusted later.

Clicker

If you are using a clicker, now would be the time to set it so that releases just at the end of the expansion phase of your shot cycle.

Stabilizers

Stabilizers are a big subject, I’ll put up a separate post of the physics of these things, but for now, we want to adjust the weights to achieve a neutral balance. There are two balance points to consider.

First, with the bow vertical but upside-down, rest the long rod on your finger to find the point of balance. Ideally, the balance point is about 1″ in front of the back of the riser (this is to allow for the fact that the balance point moves backwards when you draw the bow). Adjust the weight on the end of the long-rod if necessary (or the weights at the end of the side rods)

Having got it balanced in the front-back horizontal dimension, we now balance it in the vertical dimension. with the bow held horizontally, string up and long-rod pointing down, balance the bow on one finger. The balance point should be opposite the throat (deepest point) of the grip. Adjustments may be made by putting a weight (or taking one off) from the top rod, adjusting the angle of the side rods, or whatever it takes to make it work for both points of balance.

Dynamic setup, or Initial tuning

There is a lot that can be said about tuning, but here we are just covering the basics. This involves:

• Adjusting the button pressure
• Adjusting the nocking point height
• Adjusting the match between arrow spine and limb weight

Button pressure

Shooting at 18m or 20yds using all fletched arrows, shoot an end with the sight on the gold. Looking at the group we are interested only in their position left or right of the gold (since at this point the sight may not be adjusted so that the vertical pattern is correct).

If the arrows are off to the left, reduce the button spring pressure. If the arrows are off to the right, increase the button spring pressure. Continue shooting ends until the arrows are aligned vertically with the gold. While doing this you can also be adjusting the sight along the sight rail to correct the vertical.

Nocking point height

At the end of the above stage, the group should all be in or clustered around the gold. Now you need two unfletched (bare shaft) arrows. Shoot these along with your fletched arrows in random order and observe the groups. There will likely be two groups, the fletched arrows in or around the gold, and the bare shafts either above or below them. You need at least two bare shafts because if there is only one you can’t tell whether the difference is due to tuning or a poor release on that one arrow. Assuming the two bare shafts form a group (and the fletched arrows also form a group), if the bare shafts are above the fletched arrows this means that the nocking point is too low, which the fletchings are compensating for. You want the fletchings to do as little work as possible, as otherwise they introduce too much drag. So move the nocking point up a millimetre and try again.

If the bare shafts are below the fletched arrows this the nocking point is too high (ie the arrow is pointed down too much at full draw), so move it up a little.

Continue until the fletched arrows and bare shafts are at the same vertical level.

Matching limbs to arrow spine

At this point, the bare shafts and fletched arrows are in two groups at the same height on the target. If they are also at the same horizontal point (ie if all the arrows form one group), congratulations, you have finished initial tuning.

In the discussion below, when I talk about the bare shafts going left or right, I’m referring to a right hand bow (ie held in the left hand). If you are left-handed, just reverse what I say below.

Adjusting the bow to match the arrow

Assuming you are not that lucky, this means that the spine of the arrow is not well matched to the power delivered by the limbs. I’ll make a separate post explaining arrow spine and the action of the string on the arrow, but for now it is enough to know that the arrow does not stay straight. When you release the string the arrow bends, first one way and then the other. Because of this bending the arrow curves around the bow (archer’s paradox) emerging from the bow (when tuning is complete) straight down the true centre of the bow. The more powerful the limbs (basically, the draw weight, although this is also influenced by the efficiency of the limbs as shown by the draw-force curve, but let’s leave that discussion for another day), the more the force acting on the nock causes the arrow to bend. To compensate for this, stiffer arrows are needed for stronger bows, and more flexible arrows with weaker bows.

When you bought the arrows, you presumably looked up the arrow charts to choose arrows with a spine suitable for your limbs (or somebody did on your behalf). However, this isn’t exact, it may need a little adjustment to get it exactly right. The main adjustment is to change the bow weight by adjusting the limb bolts. As the limbs are adjusted out the draw weight decreases. When the limbs are adjusted all the way into the limb pocket base the bow is at its most powerful for those limbs.

If the bare shafts go out to the left (while the fletched arrows are in the gold) then the arrows are too stiff for the current setup. To compensate we tighten the limb bolts to increase the draw weight. If the bare shafts are off to the right then the arrows are too weak, so the limb bolts need to be slackened off, reducing the power.

Adjusting the limb bolts is one possible adjustment at your disposal. Another is the bracing height. The bracing height is adjusted by adding or removing twists from the string; the more twists the shorter the string and so the greater the bracing height. Start with the bracing height in the middle of the range recommended by the bow manufacturer. Why does this make a difference? Because when you release the string the nock actually moves towards the riser in a sine curve. At some point the limbs reach the limit of their movement and the string suddenly stops moving forward, causing the nock to detach. At what position in the sine curve did the detachment occur? This is what you are adjusting when you change the bracing point. By changing it up and down (within the manufacturer’s limits) you can cause the arrow to be pointed more to the left or the right at the point it detaches. In addition, however, the brace height may affect group size, so this is a more delicate adjustment that changing the limb poundage.

A further change is possible by using a different number of strands in the string. Although the string may seem very light to you, remember that it is the part of the bow that undergoes the greatest change in position, and Force = mass x acceleration, so a change in the mass of the string can have a significant effect on the force applied to the arrow. Commercial strings are made so that they are suitable even for powerful bows, for safety reasons, and commonly come in 18 strands. For a bow in the 20-26lb range this is overkill, and the number of strands reduced to 12-14 (or even down to 10) safely, which will increase the speed of the arrow, and thus how much it bends. that is, you can ‘weaken’ the arrow by reducing the number of strands, if the bare shafts are going off to the left (for a right-hand bow).

Adjusting the arrow to match the bow

If the above procedures don’t work, and you cannot get the bare shafts into the same group as the fletched arrows by adjusting the bow, then you will have to adjust the arrows to match the bow.

If the arrow type permits different point weights (eg X10s), then if the arrows are too stiff increase the point weight; if too weak, reduce the point weight.

If all that fails, then I’m afraid these arrows are just too far out to be matched to the bow. If the arrows are too weak, and you have access to an arrow saw, then shortening the arrow will make it stiffer. Of course, this assumes that you have some leeway here, and shortening them will not make them unsafe – don’t shoot arrows too short for your draw length!

If the arrows are too stiff, then there is nothing for it but to replace them, either with the same spine but longer, or the same length but a weaker spine.