Bowstrings part 1: bowstring basics
Starting a new series, Cleve Cheney looks at bowstrings – the requirements for a good string and the materials such strings are made of.
Bowstrings are often overlooked in terms of importance – until one breaks, that is, and the bow becomes inoperable. The string is one of a bow’s critical components. You can shoot a bow without a sight, without a stabiliser, arrow rest, or limb savers, but you cannot shoot a bow without a string. It therefore makes good sense to learn more about bowstrings, how they are made, how they function and how they are maintained.
Strength is of paramount importance, as breakage renders the bow useless and in the case of high-poundage bows can result in injury to the shooter and damage to the bow itself. Lighter string material generally translates into higher arrow speed as there is less string mass to accelerate. The individual fibres making up the string material are subject to destructive friction each time a string is drawn and released to propel an arrow on its way. High abrasion-resistance properties will impart a longer life to the bowstring. If bowstring fibres absorb water it will weaken the string, therefore it is desirable for the string to be water resistant or water repelling.
Archers, from the very primitive to the modern, have always looked for bowstring material with a minimum of creep and stretch.
Creep is a permanent lengthening of a bowstring when it is stretched during the power stroke. The string does not return to its original length when the stretching force is relaxed. The main advantages with string materials that have low creep properties is that the draw length, brace height and cam timing of the bow stay relatively constant regardless of variations in humidity, temperature or age of the string. The end result is consistency from shot to shot.
Stretch is a temporary lengthening of the bowstring during the power stroke. The string returns to its original dimensions once the stretching force is relaxed. The advantage of low-stretch materials is that more of the effort you put into drawing the bow is transferred to the arrow. For example, approximately 20% of the total draw energy is lost due to string stretch in a B50 Dacron string. A small amount of stretch does however help to protect the bow limbs, especially limb tips, from excessive shock and is desirable in wooden longbows and recurves. Low-stretch bowstrings are very harsh on bows that were not designed for them. It is therefore not advisable to use low-stretch bowstring materials on wooden longbows and recurves and on older, steel-cable compounds. On these bows rather use B50 Dacron, unless you know for certain that the bows were designed for low-stretch strings.
Simple bowstrings may be made of any fibre twisted into a single cord and have been used in many parts of the world. They are quick to make and effective, but they unravel easily if not kept under tension. Weight-for-weight they are not very strong or durable. See Figure 2.
Reverse-twist bowstrings are made up of several bundles, each being individually twisted in one direction. The entire group of bundles is then twisted in the opposite direction. See Figures 1 and 3. The resulting string is stronger for its weight than a simple string and holds together better, with less tendency to unravel. A further advantage is that the full thickness of the string passes around the nocks, where stresses and wear are the greatest. The string can then be tied onto the nocks with a bowyers knot (timber hitch) or a Flemish loop tied in. The traditional Flemish string has a laid-in loop at one end, which makes it easier to attach it to the nock when stringing or unstringing than with a knot. A Flemish string is more difficult to make than an endless-loop string but is preferred by traditionalists.
Endless-loop strings are made of one or more continuous loops of material, parallel to each other and each pulling independently. See Figures 1 and 4. Bowstrings for modern compound bows are made this way, but it is not a modern technique. The Turks and other bowyers who manufactured composite bows used endless strings made of silk. An endless string has several advantages. It can be made to exact length, and if it is carefully made, the tension can be evenly distributed at all points on all strands. Also, an endless string is not twisted. Each strand is therefore more like a bar than a coil, and this results in less stretch when it is shot. An endless-loop bowstring is also easier to make than a Flemish string.
Let’s look in more detail at flax, hemp and stinging nettles. Flax, also known as linen, can be grown in your own back yard (hemp, or dagga, as it is more commonly known in South Africa, can be grown in your neighbour’s yard). It is best harvested at the end of autumn or in early winter when the stalks are dry. Plants are pulled from the ground with the roots intact and left to lie on the ground. They are turned every week or so until the stalks are brittle. The inner fibres are then easily extracted by combing them free from the stalks. Once gathered, the fibres can be stored for years. Seeds can also be collected and pressed to extract linseed oil, which is a traditional bow finish.
Hemp (marijuana) originated north of Tibet. It reached China by 2800 BC, Europe by the fifth century and America in 1645. It grows in thin stalks, up to four-and-a-half metres tall, and is branchless. Hemp fibres can easily be as long as a bowstring and require little twisting. Hemp is harvested and processed in the same way as flax. Because of the narcotic properties of the leaves, it is illegal to grow hemp in South Africa.
Nettles produce one of the strongest of natural fibres, but processing this plant is labour intensive. It is harvested when fully grown or dying by being pulled out of the ground and allowed to age for a while before being boiled to release the plant fibres. An alternative is to soak the stalks in water, then gently pound them. Another option is to pull fibres from broken sections of stalk.
Sinew can be bought from butcher shops or harvested from hunted animals. The backstraps or leg sinews from any hoofed animal will make useable bowstrings. The sinews can be allowed to air dry and can be stored indefinitely. Once dried, they can be pounded and shredded to obtain fibres from which strings can be produced using reverse-twisting techniques (see Figure 6).
Gut strings are the fastest and easiest to make. To make a bowstring, wind out sufficient gut and twist the strands tightly together. Then, keeping the string under tension, let it dry in place.
In the next article we will look at modern bowstring-making materials.Updated: Wednesday, October 7, 2009 12:23 PM