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STRINGS AND THINGS I am a bit obsessive about strings and all the bits and pieces that go with them. I always remember the advice I was given by a veteran coach, when I first started shooting. He really had seen it all. When he started, all bows were longbows, sights were not allowed, steel bows were a new-fangled novelty and linen strings the standard. He said words to the effect that: "the string the nocking point and the arrow rest are the only things that actually touch the arrow - choose them carefully and look after them properly, or you're just wasting your time!" He was right... Modern bowstring materials have been developed to minimise creep and stretch and maximise strength and durability. 'Creep' is permanent lengthening and is always bad news, 'Stretch' is temporary lengthening during the power stroke. A small amount of stretch is useful, as it helps protect equipment from excessive shock and vibration. The key advantage of low creep materials is that, provided your strings and cables are well made, bracing height, draw length and cam timing stay where you put them, regardless of temperature, humidity or (up to a point) age. This means that, all other things being equal, the shot is identical every time. The advantage of low stretch materials is that more of the effort you put into drawing the bow is transferred to the arrow. This is much less important now than it used to be, but it is a sobering thought that around 20% of the total draw energy is wasted by string stretch in a B50 Dacron string. So, in other words, with modern materials, the bow is easier to draw, the shot is more consistent and the arrow goes farther. Sounds good to me... However, low stretch materials come with a health warning: they are very harsh on the bow. For this reason, you must not use low-stretch fibres on bows that were not designed for them. Unless you know for certain that it is okay to do so, do not shoot anything other than B50 Dacron on wooden-riser recurves, steel-cabled compounds or anything described as or looking like a 'training bow'. (Surprisingly, low-stretch fibres are fine on traditional all-wood bows and I have shot my English longbow with a Fast Flight string for over 10 years with no problems. Traditional string materials, such as linen, hemp and silk, had a lot of creep but almost as little stretch as the very best modern fibres.) Strength and durability are simply not a problem for any string properly made with modern materials (I exclude Dacron here). With the breaking strain of a typical string being around 2000lb and a life expectancy of hundreds of thousands of shots in laboratory conditions, a single string could, in theory, last a lifetime. In practice, strings rub and wear, particularly at the nocking point and over the cams, and they degrade in sunlight. Even so, if you replace your string and cables once a year and keep a constant watch for accidental damage, you should be very safe indeed, however many arrows you shoot during that year. This is the Golden Rule.
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Materials
Examples: Dacron, Fortisan Although there were experiments in the 1940's and early 1950's with a polyester called Fortisan, and even with nylon (which must have produced something more like a catapult than a bow!), Dacron was the first artificial fibre to be widely used for bowstrings. It was introduced in the late 1950's, and became the standard almost immediately, as it was such a huge improvement over anything else available at the time. It is still widely used today on training bows and older compounds. Newer versions such as B75 Dacron are available, but have little to offer over and above the original. Advantages:
Disadvantages
Breaking strain per strand: B50 - 50lb; B75 - 55lb.
Liquid Crystal Polymers (LCP's) Aramids Examples: Kevlar, Twaron, Technora These LCP's were important in their day, especially Kevlar. They still have important uses outside of archery, but have been replaced for our purposes by newer, more reliable fibres. There are still plenty of spools of Kevlar and other aramids knocking around in cupboards and tackle boxes, but they should not be used. Even when new they have a short life - often as low as 1000 shots - and tendency to break without warning. After a few years storage, especially in sunlight, they could be positively dangerous. Like Kevlar, the LCP called Vectran is prone to sudden failure and should never be used on its own, especially on compounds. However, Vectran is an important component of most Composite Fibres, such as the BCY 450 family (see below). It is heavy and therefore comparatively slow, but it has the lowest creep of any fibre yet in production - virtually zero under archery conditions. Incidentally, it is often stated that Vectran and Vectran-containing composites need a special wax to protect them, but according to BCY, the manufacturer, although there are advantages in using a wax containing silicon, this is not the case - 'any wax, natural or artificial will do equally well'. High Modulus Polyethylene (HMPE) Examples: Fast Flight, Dyneema, Spectra, Dynaflight 97, BCY 8125) Occasionally also called High Performance Polyethylene (HPPE) or High Tenacity Polyethylene (HTPE), this is currently the most important family of bowstring fibres. HMPE fibres are the standard for high performance recurves and are used on most compounds either alone, or as part of composites. As far as I can discover there are only two basic fibres: Spectra and Dyneema. These are manufactured under license in various diameters and with slightly different finishes to produce a number of different brands of string material. Probably the best known HMPE material, at least in the UK, is Fast Flight, made by Brownells, out of Spectra. The Dynaflight family and, logically enough, the various types of Dyneema are made out of Dyneema, principally by BCY in the US and Angel in Japan. Angel Dyneema has something of a cult following, especially among recurve archers, but I have no personal experience of it. Advantages
Disadvantages
Breaking strain per strand: Fast Flight - 95lb; Dyna Flight/Dyna Flight 97 - 120lb; Angel Dyneema; 110lb
Examples: BCY 450 Premium, BCY 450 Plus, BCY 452, Brownells S4, Ultracam The definitive modern fibres for compound bows. They are all mixtures of Vectran for creep resistance and HMPE for strength and durability. For example, BCY 450 Plus is two-thirds Dyneema SK75 and one third Vectran. For practical purposes, these materials do not creep at all. A new string, or one that has been off the bow for a while, will usually creep slightly as tension between the strands evens out, but should quickly settle in. None of the creep is due to the materials themselves - see the section on settling in, below. Advantages
Disadvantages
Breaking strain per strand: All are in excess of 150lb (but note the new, thinner strands now becoming popular). At the time of writing (February 2004), HMPE and composites continue to rule the roost, as far as compounds are concerned, and I have not located any radically new fibres on the horizon. If anything, single fibre HMPE's are making a comeback with materials like BCY's 8125. It is always a dangerous thing to say, but I think that, unless a whole new technology comes along, the development of new fibres for bowstrings is getting close to its end: strength, durability, creep and elasticity have all been brought to a point where they are simply not an issue any more, and only price remains. As a reaction, it seems to me that the manufacturers are now going in for tweaks and cosmetic changes. For example, there is a trend towards ever thinner strands, which is interesting, because a couple of years ago it was for ever thicker strands, culminating, as far as I know, in a proprietary string from Martin with only 4 strands. The justification for thinner strands is that it is easier to get an even tension throughout the string, which is interesting, because that was exactly the justification for thicker strands - ho hum!
Not long ago, practically all serving threads were nylon, and it is still widely used. Nylon serving threads have one advantage over anything else yet produced: they grip the string well and are much less prone to slip or open out than the more modern fibres. Quite a few compound archers, even those shooting high performance bows, stick to nylon for this reason and accept that they must check the condition of the servings frequently and replace them when necessary. Soft-twist nylon is the cheapest. It is perfectly adequate for any end-serving that is not subject to heavy wear, which means it is fine for recurves and could be used on some end servings for a compound (the ones that don't run over a cam). It is not recommended for centre servings, as it wears through too easily. Braided nylon is similar to soft-twist, but it is a little easier to work with and makes what some people consider to be better looking servings. Its main practical advantage is that it is thinner than standard soft-twist and fits better into cam grooves. Monofilament nylon is quite different from the twisted or braided varieties. It is useless for end-servings as it would slip too much, but it is ideal, almost perfect, for centre servings. It is smooth, giving a clean, fast release for finger shooters, it forms a screw thread that can be used for accurate nocking point adjustment and, above all, it is available in many different sizes, to give the best possible nock fit. The standard sizes available from archery suppliers are 0.015", 0.018" and 0.021", but many more sizes are available from fishing tackle shops as fishing line, usually in the 15 to 25 lb breaking strain range. I have often been told, and seen it written in several books and articles, that fishing line is not suitable for archery purposes, but I have used nothing else, on recurves and compounds, for over 15 years and have had no problems whatever. One important point to watch is that monofil weakens and becomes brittle with age. If you find that servings are breaking inexplicably, often within 24 hours of making them, this is probably the reason. The other likely reason is that you let the lighter flame get too near the serving when you finished it off! Pretty well all the HMPE brands are available as unwaxed serving threads as well as bowstring threads. Most are twisted and are intended primarily for end servings. Their wear resistance makes them particularly useful where the serving goes over a cam. Some are braided and intended specifically for centre serving. Angel Dyneema has a strong reputation as a smooth, strong centre serving, as does Halo, which is braided Spectra. However, both are very expensive compared to monofilament nylon which I consider to be unbeatable in this role. The main disadvantage of all these materials is that they tend to slip and open out on the string. In general, the thinner the thread, the better it will grip, and some, such as BCY black 2D thread are covered with a light adhesive coating to reduce this problem. In practice, it does not matter too much if the serving opens out a little as the string or cable strands are still well protected and HMPE fibres are so strong that I am not even sure that serving is necessary for protection, although it plays a vital role in preventing the string from coming apart! It is worth remembering that servings can open out because they are too tight as well as too loose. As with many things in archery, this is a matter of experiment and experience. String Making - Mainly for Compounds NOTE - I have had to make a lot of strings for my own and other people's bows over the past year or so, and I have completely reconsidered my method on the basis of this experience. I now recommend serving with the twist after the twists have been put in, which is just about the opposite of my original method. Oh well, we live and learn.....), Making strings and cables 1 Tools and Equipment To make good strings and cables you need a strong string making jig. The best I have come across is the Spigarelli jig, which is industrial strength and, most important, has a screw adjustment which allows you to tighten and loosen the tension on the string as you work. Frankly, most commercial jigs available in the UK are simply not up to the job, but if that is all you have, you must make the best of it, and you might think about a separate stretching device. Before getting the Spigarelli jig I used two rigging screws bolted to the wall of my garage to wind on the tension to pre-stretch the string. The only other special equipment you need is a serving tool. Although it is big and clumsy, the Beiter tool, with steel rollers (essential) is probably the best, although both the BCY and Cartel tools are reasonable. 2 How many Strands? The most important consideration when deciding how many strands to use in your strings and cables is safety. The second consideration, a long way behind, is nock and/or cam groove fit. However, as we shall see, with conventional equipment and materials, safety is not an issue. Why is safety not an issue? To illustrate, calculate the minimum number of stands you can safely use. To be very safe, use a safety factor of 10 x Peak Weight as a minimum. This is more than adequate to take into account things like the 'jerk' of the string at the end of the power stroke, and the inevitable weakening of the fibres with age and use (remember - you must always change your strings and cables at least once a year). For example, for my own bow set to 52 lb peak weight, using 450 Plus, gives a minimum of 52 x 10 / 150 » 4 strands. For a very heavy hunting bow, with a 100 lb peak (!!) the answer is still only 7, and it is virtually impossible to get any sort of decent nock fit with less than 12. In fact I use 14 - a safety factor of 3500%. So, in practice, provided you are using HMPE or composite fibres, the only thing to worry about for strings is nock and groove fit. For cables I make sure that there are at least as many strands in total as are in the string. So for my own bows with I will have at least 8 strands of 450 or 12 of 452 in each cable. I say 'at least' because I do not like fewer than 4 strands of 452 or 6 strands of 450+ where the cable divides over the bobbin. This means that for a conventionally cabled two-wheeler, if the 'Y' is made by dividing the cable rather than having a separate yoke (like Hoyt) the minimum number of strands is in fact 16 or 24 respectively. This is probably over-kill, but it is very safe and has no unwanted side-effects. If you are using Dacron for your strings, you are still very safe indeed if you let nock fit dictate. I presume that no-one uses Dacron for cables. 3 Laying out the strands
Pre-twist and pre-tension
Serve and finish
Settling in With modern materials most, if not all the initial creep of a new string is caused by uneven tension on the jig, or by slippage caused by poor finishing, not by elongation of the strands themselves. A pre-stretched, pre-twisted string carefully made according to these instructions will not have either of these deficiencies and consequently needs hardly any settling in at all. In general, all the settling that is going to happen will happen in the first 2 dozen shots, and will be very minor at that. I expect my peep to stop rolling and come to its final position in a dozen shots and I am rarely disappointed. I have seen too many archers moaning that their strings and cables 'still settling in' after half a season when in reality, they are not settling in at all, they are coming apart! And, I might add, some of the worst culprits are commercially made strings and cables. Apparently one major manufacturer advises that it takes 1000 shots or 1 dry fire(!) to settle in a new string or cable. This is nonsense, driven more, I suspect, by the litigious nature of the American legal system than by technical reality: if your string or cables are still creeping after a couple of hundred shots, replace them with some properly made ones before they come apart and do serious damage. The most useful guides to bowstrings are :
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