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Trees

Fractures of trees at forks

The easy way, convenient for use in field conditions, non-threaded rods and no nuts may be used. The purpose of the nuts may be a washer placed on the rod, the end of which is slit and bent, flattened, etc.. (drawing).

Drawing. Bar end replacing a nut in certain bond types (cutting open and unfolding, fold, flattening).

The bar passing through the limb in most cases is not perpendicular to the axis of the bundled limbs, and thus also to the plane of the elliptical washer. In such cases, it is necessary to use washers of unequal thickness (wedge). Their task is to better transfer the force acting obliquely to the elliptical washer and to prevent the rod from bending when twisted. Therefore, the angle, formed by the planes of the wedge washer, should correspond to the angle, by which the binding bar is deviated from perpendicular to the limb axis (drawing).

Drawing. The method of making the handle in the case of an oblique passage of the binding rod: a - by installing a wedge washer, b - by welding at an angle a flat washer.

Since such a deviation should not exceed 30 °, most often it ranges from 10-20 °, therefore, the angle of the washers used should differ by 10 °. So it is enough to prepare washers with an angle of 10 °, 20°, 30°. The use of washers with such angles forces to accept a fit tolerance within 5 °. This inaccuracy is of little practical importance. Making wedge washers is a bit tricky. The easiest way is to make them rectangular and tuck one end over, giving an angle of about 10 °, or obtained by bending from a flat bar. A washer with a diameter slightly larger than the nut should be placed between the nut and the wedge washer.

Conical washers can also be used instead of wedge washers, whose operation is similar. It is essential to place the washers under the conical washers, better distributing the pressure forces on the elliptical washer. A fairly simple solution to replace a wedge or conical washer and nut can be a fastener (by welding) to the end of the round washer rod at the required angle (Lynx. b).

The element directly connecting the branches is usually a steel bar. Round bars are used for this purpose, smooth, with diameters of 8-16 mm. The bars can be uniform or connected and create rigid or flexible bonds.

In some cases (healthy hard wood, low tensile forces) you can use different hooks that are screwed into the wood by drilling a slightly smaller hole. Bars passing through two opposite branches should lie on the same straight line. An exception may be the binding of thinner side branches to a thick trunk. Drilling holes along the same straight line in thick trunks can make the hole length much longer.

The site of bonding between the two limbs at risk of breaking may be different (drawings), however, not accidental.

Drawings. Diagrams of various types of rigid and flexible bonds used in various cases of tying limbs of similar sizes.

Winds are a very important factor to take into account when setting up a binding (drawings), their strength and directions, wood quality of the protected branches and the mechanical condition of the fork.

Drawings. Examples of bundles of limbs of various thicknesses and positions.

Under certain conditions of the arrangement and quality of the branches, wind can stress the bond and create a torque on the place where the washer is applied, leading to limb fracture at the binding site (drawing).

 

The greatness of this moment, that is, the breaking force, will be the greater, the lower the bond is assumed. In contrast, the risk of fracture is greatest in trees with rotten or soft wood. Therefore, in such cases the binding should be placed as high as possible. If, on the other hand, the same branch is affected by the wind force from the outside, then there will be a loosening of the binding, and after the gust has ceased - the limb retracts and jerks. If such movements are characterized by high frequency and speed, they can damage the bond and destroy the wood in the vicinity of the bonding elements. For these reasons, under these conditions, the bond should not be placed high. The most recommended is then a low-set rigid bond with a tube placed on the rod, preventing the mentioned approach and jerking of the binding.

Drawing 1. The wind that stretches the mate causes the torque, which can lead to fracture.
Drawing 2. The action of the wind may cause the binding to relax and the occurrence of jerks on the return movements.
Drawing 3. Approximating the limbs before setting the bond allows the length of the bond elements to be determined and the required slight tension to be obtained.

The occurring winds can also cause movements transverse to the binding direction, the stronger, the higher the bond is. So that these movements are not transmitted through the rigid binding bar to the side walls of the wood hole, it is necessary to use the appropriate linkage joints, which relieve pressure and shock from transverse directions. They are flexible bonds.

However, even, when elastic constraints are used, lateral pressures of the rod on the wood of the holes can be large and cause fissures and irritation and injury to the healing tissue. In such cases, it is necessary to place a washer on both sides of the limb.