Tendon coating

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A sinew (engl. Sinew-backing ) is a Bogenbau used, antique organic fiber composite material , consisting of animal tendons and animal glue. A tendon covering is usually an integral part of a composite bow, but is occasionally also needed to prevent a damaged wooden bow from breaking.

species

There are two types of tendon coverings:

Free tendon coating (cable backing)

A free tendon coating is when a string of animal tendons (so-called cable) runs from one end to the other on the tension side of a bow (not to be confused with the bowstring ). This cable is usually tied to the wood, more rarely it runs in a specially carved groove so that it does not slide sideways from the wood when the bow is pulled. The purpose is so that when the bow is pulled, the tendon cable is stretched, absorbing much of the pulling force and thus protecting the wood from tearing.

In the past, this was necessary in areas where only very poor archwoods grew, for example at the Arctic Circle , in order to B. to build a usable arch from fir wood .

The advantages of the free tendon covering are its ease of manufacture and the possibility of twisting the cable more tightly and thus increasing or reducing the tensile weight of the bow. This was used z. B. with the Eskimos .

Firm tendon covering (tendon backing)

A firm tendon covering is also glued to the back of the bow and is as hard or harder than the wood underneath. Historically, it evolved from cable backing , which was first in use before glue was invented. The firm tendon covering is a light, yellowish-gray, hard, fiberglass or plastic-like layer that completely covers the wood of the arch back and can no longer be detached from it non-destructively (except by soaking it in water). Here the tendon fibers are embedded in a matrix of glue (see manufacture).

The purpose of the firm tendon covering is sometimes to protect brittle bowwoods from breakage, but it is mostly used to make high-quality bowwoods (and / or horn) even more efficient ( composite bows ). The best hand and crossbow bows in history had a firm sinew coating.

Advantages and disadvantages

High resilience

The biggest advantage of the firm tendon covering is its high resilience under tension, which made the development of the most extreme bow designs possible. For example, very short rider bows, reflex bows, bows with strongly curved limbs (recurves), and bows with stiffeners (Siyahs) could be developed. In fact, most bow types with tendon coverings are all of this at the same time: They are very short, highly reflective and they have recurves or siyahs. These design features, individually or in combination, ultimately result in a greater range and penetrating power, as well as a flatter trajectory for the arrow.

Long life expectancy

Another advantage compared to simple wooden bows is the long life expectancy of a bow with tendons: Although the tendon fibers in the covering can wear out just as much as the wood with bare wooden bows, the bow with tendons can regenerate quickly. It just needs to be relaxed and taken to a warm, dry place. There the tendon fibers contract under the influence of heat, which gives the bow new elasticity after a few days or weeks, so its tensile weight increases again. A good composite bow can therefore sometimes shoot for over a hundred years, since it always regenerates when not in use. It is not exactly known which process takes place in the tendon covering of a braced bow when it regenerates; The currently most popular theory states that a chemical reaction, a type of polymerisation, takes place in the finished tendon covering of a composite bow . Since tendon fibers and animal glue are made of the same material, namely the protein collagen type I, it could be that the collagen molecules in the tendon lining become increasingly interlinked (polymerize) over time, which leads to a continuous, slow shrinkage of the lining; this gradual shrinkage increases the pretension and thus the tensile weight of the bow over the years. The wear and tear of the arch through use is thus repeatedly compensated for by the slowly progressing polymerization, which is apparently favored by heat. The only thing that is certain is that if a bow is not used for years, it can gain significant pulling weight, sometimes abnormally. One only has to think of Odysseus , whose bow, after decades of absence, could not be drawn by anyone but himself (with divine help).

Water-sensitive, complex production

The biggest disadvantages of a firm tendon covering are its sensitivity to water and the comparatively complex manufacturing process, which, however, is not too important in view of the long service life. Bows with a firm tendon covering were used by very many peoples, in the last 2500 years e.g. B. from: Scythians , Persians , Egyptians , Greeks , Romans , Huns , Mongols , Turks , Crusaders (crossbow bow), Chinese , Indians , Comanche , Sioux , to name just the most famous.

raw materials

Tendons from cattle , elk , deer , reindeer and buffalo were preferred, especially the foot tendons, Achilles tendons and back tendons , as these are up to 50 cm long. Pork ones are not well suited because their fibers are wiry like horse hair. Furthermore, tendons from alligators , ostriches , horses and various exotic mammals (such as the kangaroo ) have been successfully tested by modern bow makers .

At glues are hide glue , isinglass (swim bladder) or rare casein suitable. The best natural glue that Hausenblasenleim (from Stockhausen, Donau sturgeon ) was sometimes added to increase the adhesive strength, z. B. with the Turks.

Manufacturing

Dried animal tendons are pounded soft with a hammer or stone until they split into their fibers. The fibers are combed to free them from the remains of the tendon sheath. The fibers are then washed and degreased and, after drying, combed again. So you are ready to fill the arch.

The wooden, freshly sanded arch spine is roughened a little, then brushed with warm hide glue .

Then the tendon fibers, laid out in handy bundles, are dipped one after the other in warm hide glue until they are soaked. The fiber bundles soaked in this way are then laid lengthwise on the arch, overlapping each other like a roof tile , and smoothed or combed until a continuous layer covers the entire arch spine.

The fresh covering is immediately wrapped tightly with a piece of fabric to press out excess glue. The sheet must then dry for several weeks before the wrapping is removed and the next layer of tendon fibers is glued over the first, whereby the fiber bundles of the 2nd layer must not overlap in the same places as those of the 1st layer, etc. This gluing process, Wrapping and drying continues until all layers have been applied. The number of layers depends on the type of arch.

During the weeks of drying time, a string is usually stretched between the ends of the bow, that is, the bow is tensed upside down when a fresh layer of tendon dries, so that the wood does not warp due to the damp glue.

As the individual tendon layers dry, they contract lengthways and create a dry tension, which causes the bow stick to curve forward towards the surface. There is a permanent bending back of the arch, it is called a reflex . In extreme cases (e.g. Turkish bow) the bow stick looks like the letter C from the side.

Final drying and finishing

The final drying process can take several months or up to two years, depending on the thickness of the tendon covering. During this time, the reflex (bending back) increases more and more, so that the tension cord must be tightened between the ends of the arch so that the wood does not warp sideways.

At the end of the respective drying time, the tension cord between the ends of the arches is removed, as is the wrapping of the tendon covering. Now the bow can be tilled normally so that it bends correctly, then it is shot in. Finally, a layer of thin leather, birch bark or the like is applied. glued to the covering to protect it from water. Most tendon-covered bows are then varnished .

The reflex of the tendon coating that occurs during drying is responsible for the regenerative capacity (see above) of the occupied bows, as in the finished bow after the bowstring has been tensioned, it always pulls the two limbs forward, so that the weapon recovers quickly, especially through heat. The reflex causes the long service life (and the devastating penetration power) of most tendon- covered bows, which is why they are sometimes also called reflex bows. In this context, reflex is simply the bow-maker word for the same force that modern engineers call prestressing today; just like with prestressed concrete , it makes the arches more stable, more powerful and more durable. Since arches were covered with tendons as early as the Stone Age / Bronze Age, this technique can be regarded as one of the first conscious applications of prestressing.

Today, this old fiber composite technology is rare, even among experienced bow makers, as it is too complex and expensive.

But it is still known in some Asian countries, such as Tibet , Mongolia and Korea .

swell

  • The Bible of Traditional Bow Making Vol. 1–3, Verlag Angelika Hörnig, ISBN (Vol. 1) 3-9808743-2-X

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