SHOOT-THROUGH CABLE SYSTEM
The shoot-through cable system is difficult to describe, but once you have seen one (and I presume most of you have by now) it is pretty obvious. It is also pretty obvious that it is an improvement in almost every way on dragging the cables sideways over a cable guard. When I installed my first shoot-through system on my Hoyt Oasis the difference was amazing. The bow was quieter, faster and above all, much more consistent. My scores jumped immediately by around 5 points on an IFAA Field Round.
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Norwegian
International,
Terje Roestad using a Merlin shoot-through system |
The only problem I have ever come across is that the cables can rub along the arm of archers who use a very straight bow arm. In this case, a long, 'beginners' bracer can often put things right - I always wear one .
Making a Shoot-Through Cable System
Making a shoot-through cable system is quite straightforward, although I would not advise a beginners at string making to try it by themselves.
All shoot-through system depend on splitting the cables. There are two common ways of doing this. One, developed by Don Kudlacek, whose company is best known for their 'Genesis' multi-rod stabilisers, uses no proprietary parts. Each cable is a single unit, split and separated by scrap lengths of ACE or ACC 3-18 tubing with G-nocks at each end. The other developed by Merlin Bows of England (http://www.merlin-bows.co.uk) uses proprietary, metal half-moons. In this case there is a separate short cable attached to the cam at one end and the half-moon at the other, and a single, double length cable run over the half-moon.
Each system has its advantages. The Kudlacek system lets you adjust the tension separately on each side of the limb. This positively controls limb twist and makes it the ideal system if you are unsure about the state of your limbs, and also for any split-limb bow, as limb twist is always a major concern with this system. of course, you must ensure that the tension on each side of the limb is correct, or you could twist a perfectly good limb. The Merlin system evens out the tension from side to side, as the single cable can move over the half-moon, so it is ideal for untwisted, solid limbs, but can't be used to correct pre-existing limb twist, nor to control split limbs or other dodgy designs. It is easier to make the Merlin cable system, once you have the measurements, and I have used it almost exclusively over the past three or four years.
Shoot-through systems can be installed on any two-wheeler provided it has, or can be fitted with, axles that extend on either side of the limb, and bobbins to attach 'Y' shaped cables. These days, that covers nearly all bows.
Whichever system you use, it is important to get the measurements right:
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Measure the axle-to-axle distance with the bow at rest.
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Put the bow in a press.
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Remove and measure your existing cable.
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FOR THE KUDLACEK SYSTEM: Make two cables, each three-quarters of an inch longer than your existing cable to allow for the fork you will put in them.
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FOR THE MERLIN SYSTEM: Make four cables. Two will must be the length of the cable take-up plus about 6 inches. In practice, unless you have unusually large cams, 9.5 inches will be about right. The other two are difficult to calculate, but easy enough to measure. Relax the bow in the bow press until it is back to the correct axle-to-axle length. Make and fit one of your short cables and half-moon. Use a single strand of bowstring material to imitate the long cable. Measure and add half an inch.
If you are prepared to take a bit of a gamble, or want to double check, you can use the formula:
2x (length of original cable - length of short cable) + 1.75 inches
For example, if your original cable was 42.5 inches, your new cable will be:
42.5-9.5 = 33 x2 = 66 + 1.75 = 67.75"
This will usually be about right - a little on the long side, if anything, which is easily fixed by a few twists.
The starting point is the number of strands you use in your string, but there are a few points to remember:
FOR THE KUDLACEK SYSTEM: Since the single cable divides twice - once at the root of the 'Y' and once more to go over the bobbins - the number of strands must be divisible by 4 to have equal numbers on each side of the 'Y'. If necessary, round up to the nearest number that is divisible by 4. For most standard threads (eg BCY 450, FastFlight, Dynaflite etc) this means 12, 16 or 20 strands. 12 is a realistic minimum, and since even this means that only 3 strands will go over each bobbin, you may feel, like me, that 16 strands is as low as you want to go. On the other hand, don't overdo the safety factor, as 20 strands may well over-fill your cable groove. For my own 52 lb bow, with a 14 strand string I use 16 strands for the cable.
FOR THE MERLIN SYSTEM: Use the same number of strands as in your string for the short cables. The long cables only divide once, at the bobbins, so use half the number of strands as in your string, rounded up if necessary, to be divisible by 2. For my own bow, with a 14 strand string, I use 14 strands for the short cables, and 8 strands for the long cables.
Once you have established the measurements. making the cables is standard, if fiddly: just be particularly careful about lengths and keeping constant tension. There is no need to serve any of the end loops.
Merlin-type cables are very easy to fit. the short cables are served for their full length, so they need no twists. I would put about 20 twists in each of the long cables to start with and take it from there (see below). Although the system is self-correcting, it is still a good idea to put an equal number of twists into each side of the long cable when making adjustments on the bow.
When fitting Kudlacek-type cables, it is important not only to get the overall length right, but to ensure that each arm of the 'Y' is equal (or not, if you have a twisted limb!). The best way to do this at this stage is to ensure that the axle-to-axle distance is identical on each side of the limb; you will carry out fine adjustments later.
In a variation of the original Kudlacek system, separate, short cam cables are used, as in the Merlin system and looped directly onto the long cables. This is easier to make, but means that you no longer have control over limb twist - what you now have is simply a cheap version of the Merlin system.
Adjust the cables and, where necessary the string, to get the correct draw length, then the correct axle-to-axle length to about one-eighth of an inch either way. The key rules are:
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The draw length varies in the same direction as the string. Lengthening the string lengthens the draw, shortening the string shortens it.
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The draw length varies in the opposite direction to the cables. Lengthening the cables shortens the draw, shortening the cables lengthens it.
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Adjust draw length first, then adjust axle-to-axle length by equal adjustments of string and cable in the same direction. If the axle-to-axle length is too long shorten both the string and the cables equally and vice versa.
This may sound complicated, but like many things to do with strings and things, it is quite easily sorted out in practice.
Finding the 'Correct' Draw Length
There are two answers to the question 'what is the correct draw length?'. The first, and ultimately most important, is that it is the draw length that allows you to be comfortable and in control of the bow. However there is also an engineering-type answer: it is the draw length that gives maximum bow efficiency and let-off. For most wheel/cam designs, there is an acceptable draw length range of about half to three-quarters of an inch downwards from the quoted, draw without the need to adjust or replace the wheel or cam itself. For example, a bow quoted as having a draw length of 29 inches will probably be fine from about 28.25 inches to 29 inches (not longer than the quoted figure, you notice - you will see why later). If you want to go outside this range you will either need a different sized cam or, with luck, you may be able to adjust or replace just the cable segment of the cam.
If you go much below the quoted draw length, by adjusting the string and cable lengths you will get quite quickly to a point where power loss is dramatic and, perhaps more important with modern hard-cam, short-valley bows, you will find that your holding weight quickly increases to the point where it is uncontrollable. On a round, or round-ish wheel, the ideal draw length (from the bow's point of view) is where the string nearly wraps the whole way round the cam, but not so far that it traps itself - see "too long" below.
On more radical cams, the correct length is usually indicated by the alignment of the string with the 'tail' of the cam.
Once the cables are fitted and both the axle-to-axle length and the draw length are correct, set your timing as in the 'Basic Set-up' section. If you wish, you can then proceed to 'Cam Tuning' in the 'Super Tuning' section.