Tillern

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The tillering is a term of archery from the craft of bow maker in the workflow in bow making , in particular the Langbogenbau . Tillern describes the work process in which the bow maker brings the preformed bow blank from the stave into its final bending shape by machining - by coordinating the strength of the upper and lower limbs until both bend as desired and evenly without kinks when the bow is pulled out . The process can take several hours and the work step can take days. It is the last operation on the limbs before they finish .

The tillering is one of the highest craftsmanship art crafts and - skills in the skill of the bow maker.

Goal setting and process

The aim of tillering is good shooting comfort, high strength and resistance to breakage of the bow and low string follow with the lowest possible moving mass of the limbs, and for this an even tension distribution in the bow and in particular the limbs is necessary without tension peaks when the bow is drawn out and fully extended.

To do this, the bow maker initially uses the draw knife , later the finer tail plane and scraper , with which, depending on the type of bow, he removes wood along the belly (inside), back (outside) or side or all three until the limbs have the desired even curvature when drawn out demonstrate. Every time after a few shavings , he fixes the blank, which is initially stretched with an over-long Tiller tendon, in the Tiller board, which is usually attached parallel to a wall . With its pull-out device over a pulley , so that he has a clear distance, the bow maker pulls the bow out again and again and piece by piece, checking the curvature and bending behavior with eye and feeling . From time to time he shortens the tendon until it has its future length at the end. In a variant of the tiller board, the bow is drawn out directly by hand and the string is hooked into a series of notches with increasing extension, the bow maker can thus assess the static curvature at a certain extension length, but not the dynamic bending behavior. Tillern also serves for the final adjustment of the draw weight of the bow at a certain draw length , the fine tuner , in which grinding tools are also used. Because woods are natural materials, the bow maker occasionally takes breaks of hours or days. The Tillern can therefore extend over several days.

During the tillering process, the bow continuously loses its final draw weight due to the material removal. The draw weight is always highest at the beginning of the tillering and always lowest at the end. Every tiller process weakens the bow. There is a risk of Überertillern . If the bow is made of natural materials, it may be necessary to adjust it after some time or use .

The bowmaker cannot make up for lost pulling weight after too much material has been removed, but at best within limits through backing measures , such as B. Cover with rawhide , tendons or snakeskin, or glued circumferential windings made of yarn or animal tendon compensate for the weakened areas.

The wood removal follows the longitudinal fibers , the "muscle fibers" of the bow, and must not cut them, especially on the back that is under tension . An incision interrupts the force tension of the affected fiber bundle over the length of the bow , it becomes ineffective dead mass and the area becomes a weak point. The limb can fray at this point and kink, tear or break. Therefore fiber layers are removed. If the fiber course of a blank is wave-like or if there are knots in the blank, the arch builder follows the course with the tool and the arch shows snake-like turns or rounded bulges at the end. This is not a quality defect, nor a design gimmick, but a technical necessity that also gives every solid wood arch its unmistakable appearance.

At which points and how much the bow maker removes is determined in addition to the bow material used, the chosen bow type and design, the layout and its course of the cross-sectional area and neutral fiber . The selected types of wood, due to their different mechanical pressure , stretch and hardness properties, have a decisive influence on the arch type and layout. (Among other things, the bow layouts therefore differ in different epochs or regions of the world - bows were built from the materials and woods that were available at the time and region.) This includes the cross-sectional geometry of the limb and its course from the middle part to the limb end crucial. The English longbow made of yew, for example, has a D-shaped cross-section that tapers from the middle part to the tips. The American longbow and flat bows , often made of Osage orange , have the eponymous flat rectangular cross-section, in which the limb width is much greater than its thickness; the cross-section also tapers towards the tips, but more in width than in thickness. The type of bow of the Holmegaard bow , a more than 10,000 year old layout, which had a long development time behind it and testifies to the highly developed Tiller skills at that time, shows a special course and a particularly old layout as an unusual challenge of the Tillern for a bow maker . Its cross-section is initially that of a flat arch in the area of ​​the central part and changes relatively abruptly after about 2/3 to 3/4 of the limb length into an oppositely flat to round cross-section more thick than wide.

Result

With a well-tilled bow, after loosening the drawn bow with the arrow, the limbs move synchronously to each other and both tips reach their starting position at the same time, the tendon remains in the middle of the bow line when drawn out and fired, the limbs are not twisted and are straight. This makes the bow steady when fired, also by minimizing the resulting torque on the horizontal axis, the bow does not tilt undesirably forwards or backwards when fired, and ensures the best possible energy transfer from the limbs to the arrow . The bending line of the bow in its full extension is even and looks harmonious.

A poorly tilled bow loses efficiency , shoots restlessly and can break when it is pulled out or loosened . The breaking of the fresh bow due to insufficient tillerns is one of the most common disappointments of beginners in bow making without Tiller experience. Often the bow already breaks in the tiller board.

At the end of the Tillern, the bow maker measures the reached draw weight and notes it together with the associated draw length on the bow. After the final completion, the finish is measured one last time. Too great a deviation from the value immediately after Tillern is suspect and the sheet is checked again. If the value is correct, the bow maker writes the final bow length, draw weight and draw length near the middle section either on the belly side or the side of the middle section and puts his signature underneath.

The tiller

→ Main article: Tiller

The tilled arch shows a uniform bending line when fully extended . The lower limb is usually more rigid than the upper limb in order to compensate for the asymmetrical force geometry, which arises from the fact that the force point of the pulling hand usually engages the tendon below the vertical center of the bow and the pressure point of the bow hand is also usually lower in the grip. The lower limb of a bow is therefore usually shorter than the upper arm in relation to the handle. In the full extension, this asymmetry of the limb forces is just not visible because of the tilling, both tips , the limb tips , lie on the vertical.

The different bending stiffness can be seen when the bow is stretched but not extended: the vertical distance between the tendon and the limb is smaller on the lower limb than on the upper one. Due to their force connection via the tight tendon, both tips are subject to the same tensile force , but the lower limb bends less, it is stiffer. The difference between these two distances from the tendon to the limb, measured at a certain distance from the vertical center of the bow according to the AMO standard, when the bow is stretched and not extended is a key figure of the bow, it is its tiller . Usually the measuring points are at the two fade outs , the transition points from the middle section to the limb.

Parameters such as the tiller and measurement methods in archery were standardized in the 1950s by the Archery Manufacturers Organization , the AMO . Since the organization was renamed the Archery Trade Association in 2002 , the AMO standards can also be found as ATA standards .

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