Wood bending technologies. How to bend a board at home How to bend a wooden block at home

If there is a need to develop a curved element from wood, then most likely you will encounter a number of difficulties. At first glance, it will seem that it will be easier to cut the required element in a curved form, however, in this embodiment, the wood fibers will be cut and weaken the reliability of the part. Plus, when performing, a very large consumption of material comes out.

Stages of work on bending the board at home:

Wood is cellulose fibers bound together by lignin. Placing the fibers in a straight line affects the flexibility of the wood material.

Tip: a durable and reliable wood material for the manufacture of all kinds of products can only come out under the conditions that the wood is perfectly dried. However, changing the shape of a dry wood blank is a rather laborious process, since dry wood can easily break.

Having studied the technology of wood bending, including its basic physical properties of wood, allowing it to change its shape, it is quite possible to bend wood material in artisanal conditions.

Specifics of working with wood

Bending of wood material is accompanied by its deformation, stretching of the outer layers and compression of the inner ones. It happens that the tensile force leads to rupture of the outer fibers. This can be prevented if a preliminary hydrothermal finishing is carried out.

Can bend timber blanks made of glued wood and solid wood. Plus, to give the desired shape, peeled and sliced ​​veneer is used. Hardwood is considered the most plastic. Which includes beech, birch, hornbeam, ash, maple, oak, linden, poplar and alder. Glued bent blanks are best made from birch veneer. It should be noted that in the total volume of such blanks, about 60% falls on birch veneer.

By production technology bent wood, when steaming the workpiece, its ability to compress significantly increases, and specifically by a third, while the possibility of stretching increases by only a few percent. As a result, one cannot even think about bend the tree is thicker than 2 cm.

How bend board in artisanal conditions: heating in the steam box

First of all, you need to prepare a steam box, which can be made with my own hands. Its main task is to restrain the tree, which is required bend. It must have a hole that is designed to let steam out. Otherwise, under pressure, an explosion may occur.

This hole should be in the bottom of the box. Plus, in the box you need to calculate the removable cover, through which it will be possible to remove bent wood as soon as it receives the required form. In order to hold the bent wood blank in the required shape, special clamps have to be used. They can be done without outside help made of wood or purchased at a building materials store.

Several round cuts are made from wood. Holes are drilled in them, offset from the center. After that, you should push the bolts through them, and then drill another one through the sides to push them firmly. Such simple crafts can perfectly play the role of clamps.

Now you can start steaming the tree. To do this, you need to close the wood blank in the steam box and take care of the heat source. For every 2.5 cm of product thickness, the time spent on steaming will be about an hour. After it expires, the tree should be removed from the box and given to him. required form by bending. The process should be carried out quickly enough, and the bending itself should be soft and gentle.

Tip: due to the different degree of flexibility, some types of wood will bend more easily than others. Any methods require the application of various amounts of force.

As soon as the desired result is achieved, the bent workpiece must be fixed in this position. Tree fastening is possible during the process of its development new form making it easier to control the process.

How bend board in artisanal conditions with chemical impregnation

Since lignin is responsible for the stability of wood, its bonds with the fibers should be destroyed. This is achieved by chemical means, and it is quite possible to do this in artisanal conditions. The most optimal for such purposes is ammonia. The workpiece is soaked in 25% aqueous solution ammonia, which greatly increases its plasticity. The same way there will be an opportunity bend, twist it or squeeze out some relief forms under pressure.

Tip: you should look at the fact that ammonia is dangerous! Due to this, while working with it, it is necessary to strictly adhere to all safety regulations. Wood soaking must be carried out in a tightly closed container, which is located in a well-ventilated area.

The longer the wood is soaked in an ammonia solution, the more plastic it will become later. After soaking the workpiece and developing its new shape, it is necessary to leave it in a similar curved form. This is necessary not only to fix the form, but also to evaporate the ammonia. However, it is necessary to leave a bent tree in a ventilated area. It is noteworthy that when the ammonia has weathered, the fibers of the tree will acquire the same reliability as before, which will enable the workpiece to hold its own shape!

How bend board in artisanal conditions: bundle method

First you need to make a harvest of wood, which will later be prone to bending. It is very, very important that the boards are slightly longer than the length of the required part. This can be explained by the fact that the bend tames the lamellae. Before you start cutting, you will need to draw a diagonal line with a pencil. This must be done across the underside of the workpiece, which will make it possible, after moving the lamellas, to save their order.

The boards must be cut with a straight edge, and not at all with the front side. Similarly, they can be put together with the smallest change. The cork layer is applied to the mold, which can help avoid any unevenness in the shape of the saw and allow for a more even bend. Plus, the cork will hold back the delamination in the form. After that, glue is applied to the upper side of one of the lamellae with a roller.

It is best to use urea-formaldehyde glue, consisting of 2 parts. It has a high level of adhesion, but dries for a long time. You can also use an epoxy-based resin, but such a composition will cost decent money, and absolutely not everyone can give it to themselves. A typical version of glue for wood in this version is not suitable. Although it will dry quickly, it is considered too soft, which is not at all welcome in this version.

A product made of bent wood must fit into the mold as soon as possible. So, on a lamella smeared with glue, another one lies down. The process must be repeated until the bent workpiece receives required thickness. Boards are fixed together. After the glue has completely dried, it is necessary to make it shorter to the required length.

How bend board in artisanal conditions: propyl

The prepared wood cut needs to be sawn through. Cuts are calculated for 2/3 of the thickness of the workpiece. They must be inside the bend. You need to be very careful, as rough cuts can be difficult to deform the tree, and completely break.

Tip: The key to success when cutting is to keep the distance between the cuts as even as possible. The best option is 1.25 cm.

The cuts are made across the pattern of the wood. After you need to compress the edges of the workpiece, which will make it possible to combine the resulting cracks into a single whole. This shape and gets a bend at the end of the work. After which it is corrected. In many cases, the outer side is finished with veneer, less often with laminate. This action will give you the opportunity to correct the bend and hide almost any imperfections made in the manufacture. Gaps in a bent tree are hidden quite easily - for this, sawdust and glue are mixed, after which the gaps are filled with the mixture.

Regardless of the fold option, as soon as the workpiece is taken out of the mold, the fold will relax a little. In view of this, it must be made a little larger in order to compensate later this effect. The sawing method is used when bending a corner made of metal or part of a box.

So, using these tips, you can big problems bend wood with your own hands.

How to bend a board, plywood, fiberboard, MDF with your own hands

Often during the course of repair work there is a need to obtain curved surfaces of products made of wood. How to bend the board in such a way that the bend is strong and does not crack during the bending process? What if you decide to do overhaul with your own hands, then you should not retreat before such difficulties. In this article, we will talk in detail about how to give a wood material a curved shape.

How to bend a tree?

No, our task is not at all to bend an innocent plant. It's about wood. building materials. How to bend a tree so that it bends and does not break? The method of bending wooden products has been known since ancient times: to shape wood, you need only heat and moisture, under the influence of which the plasticity of the material increases with all the ensuing consequences. How to bend a tree? Hold him in hot water (the higher the temperature, the faster the processes) or steam ( a steam generator can be built from a kettle or use an iron). The higher the temperature, the faster the wood gives up and you can start bending it. Moistened and heated wood can be bent under the action of the load (the ends of the board are placed on the supports), and the load is placed in the place of the future bend. Dried wood perfectly retains the minimum radius of curvature that was achieved during the bending process. Now we know how to bend a tree, we can dwell on this issue in more detail.

The reaction of wood to external influences

The fact is that wood reacts differently to bending. The convex part is under tension, the concave part is under compression. Moreover, the material also reacts differently to steaming. For example, the ability to compress increases by as much as a third, but to stretch - just a couple percent. That is why it is not worth thinking about how to bend a board more than two centimeters thick at home. It must also be taken into account that different types Woods react differently to bending. For example, such species as oak, larch, maple bend poorly, but beech, ash, walnut - well. So before you think about how to bend the board, decide on the type of wood from which it is made.

How to bend plywood, fiberboard, MDF

At home, plywood is bent by increasing its moisture content, then ironing (an iron is required), and fixing it in a template. Any frame element can serve as a template, and its shape does not have to be curvilinear at all. The product is attached to the template with adhesive tape. Can be clamped bent plywood between two spacers, give it a bent shape due to the ropes, tying the product with them in several places along the radius of curvature. Plywood can only be used after it has dried. It seems that we figured out how to bend plywood - we move on.

How to bend fiberboard? The technique is the same as in the previous case! How to bend MDF? In this case, you can go in two ways: either bend thin sheets (no more than 5 mm) and glue them together, or use flexible MDF. in which on one side there are transverse slots. The thickness of such sheets is usually 8 mm. When bent, they overlap each other with milled sides, after which they are glued together. That, in fact, is all!

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If you decide to decorate the room with wood or start creating beautiful furniture in classical style- then you will need to produce curved parts. Fortunately, wood is a unique substance, because it allows experienced master play around with the shape a bit. It's not as difficult as it seems, but it's not as easy as you'd like.

Previously, the site already had a publication on plywood bending. In this article, we will understand the principles of bending massive board and timber, we will find out how it is done in production. We will also bring helpful tips from professionals who will be useful to the home craftsman.

Why bending is better than sawing

curvilinear wooden detail can be obtained in two ways: by bending a flat workpiece, or by cutting out the required spatial shape. The so-called "cutting" method attracts users with its simplicity. For such manufacturing of parts and structures, you do not need to use complex devices, you do not have to spend a lot of time and effort. However, in order to cut a curved wooden product, it is necessary to use a workpiece that is obviously too large, and a lot of valuable material will be irretrievably lost as waste.

But main problem are the performance characteristics of the parts received. When cutting a curved part from a conventional edged lumber, wood fibers do not change their direction.
As a result, transverse sections fall into the zone of radii, which not only worsen appearance, but also significantly complicate the subsequent refinement of the product, for example, its milling or fine grinding. In addition, in the rounded areas most vulnerable to mechanical impact, the fibers run across the section, which makes the part prone to breaking in this place.

Whereas when bending, the opposite picture is usually observed, when the wood only becomes stronger. On the edges of a curved beam or board do not go "end" sections of the fibers, so subsequently it is possible to process such blanks without restrictions, using all standard operations.

What happens in wood when it bends

The technology of bending is based on the ability of wood, while maintaining integrity, to change its shape within certain limits as force is applied, and then retain it after removal of mechanical stress. However, we all know that without preparatory activities lumber is elastic - that is, it returns to its original state. And if the applied forces are too great, then the beam or board simply breaks.

Layers wooden blank when bent, they work differently. Outside the radius, the material is stretched, inside it is compressed, and in the middle of the array, the fibers practically do not experience significant loads and have little resistance to the forces acting on the workpiece (this inner layer is called “neutral”). Under critical deformation, the fibers on the outer radius are broken, and on the inner radius, “folds” are usually formed, which are a fairly common defect in the bending of softwood. shrink fibers of plastic hardwood or conifers can be 20 percent or more, while the stretch limit is about one to one and a half percent.

That is, to determine the possibility for bending (without breaking), the limit of relative elongation of the stretched layer will be a more important indicator. It directly depends on the thickness of the part and determines the radius to be obtained. The thicker the preform and the smaller the radius, the greater will be the relative elongation along the fibers. Having data on the physical properties of popular wood species, it is possible to formulate for each of them the maximum possible ratio of the thickness and radius of the parts. In numbers it will look like this:

Bending using a steel bar

Bending without using a bar

These data indicate that softwood lumber, compared with dense hardwood, is less adapted to free bending. To work with lumber at aggressive radii, it is imperative to use combined methods of preliminary preparation of parts and mechanical protection.

Tire as an effective way to avoid the destruction of wood during bending

Since the main problem is the breakage of the fibers from the outer radius, it is this surface of the workpiece that needs to be stabilized somehow. One of the most common methods is the use of an overhead tire. The tire is a steel strip with a thickness of half a millimeter to two millimeters, which covers a beam or board along the outer radius and is bent on a template along with the wood. The elastic strip absorbs part of the energy during stretching and at the same time redistributes the breaking load along the length of the workpiece. Thanks to this approach, coupled with moistening and heating, the permissible bending radius is reduced significantly.

In parallel with the use of a steel tire in bending devices and machines, mechanical compaction of wood is achieved. This is done using a pressing roller, which presses on the workpiece along the outer bending radius. In addition, the template mold in such a fixture is often endowed with 3 mm teeth (in increments of about 0.5 cm), oriented towards the workpiece travel.

The task of the jagged surface of the template is to prevent the workpiece from slipping, to prevent the mutual shift of the fibers in the solid wood, and also to create a small depressed corrugation in the concave radius of the part (the fibers are pressed into the array, therefore, problems with folds are solved).

Pressing with a tire allows you to bend bars and boards from softwood and soft hardwood with a minimum percentage of rejects. Please note that parts made of relatively hard rocks become about ten to twelve percent thinner when pressed, and pine and spruce blanks become 20-30% thinner. But the positive aspects of this method include a significant increase strength characteristics finished product, as well as a significant reduction in the requirements for the presence of flaws and defects in wood blanks.

How to improve the plasticity of wood

In the normal state, lumber has elasticity, significant spatial rigidity and resistance to compression. These valuable properties Wood is derived from lignin, a natural "network" polymer that gives plants their stable shape and strength. Lignin is located in the intercellular space and in cell walls, connecting cellulose fibers. In coniferous wood it contains about 23-38 percent, in hardwood - up to 25 percent.

Essentially, lignin is a kind of glue. We can soften it and turn it into a "colloidal solution" if we heat the lumber by steaming, boiling, treating with high frequency current (for small parts household microwave is also applicable). After the lignin is melted, the workpiece is bent and fixed - cooling down, the molten lignin hardens and prevents the wood from returning to its original shape.

Practice shows that optimum temperature for bending solid wood (bar, rail, board) will be 100 degrees Celsius. This temperature must be obtained not on the surface, but inside the workpiece. Therefore, in many respects, the time of thermal exposure will depend on how massive the part is. The thicker the part, the longer it will take to heat up. For example, if steaming is used to prepare a 25 mm thick strip (with a moisture content of about 28-32%) for bending, then on average it takes about 60 minutes. It is noteworthy that the exposure time under steam for parts of similar dimensions for any species is approximately the same.

By the way, it is believed that it is also impossible to overheat the part, since lignin after hardening can lose elasticity and become too brittle.

The boiling method is not often used, since the workpiece is strongly and unevenly moistened, and such water-saturated fibers and cells, when bent, can tear, at least with the formation of a pile. Parts after cooking have to dry for too long. But this method shows itself well if you need to process only part of the workpiece for bending.

Steaming allows you to heat the workpiece evenly, and its humidity at the exit tends to approach the optimum. The most suitable humidity for achieving maximum plasticity of lumber is considered to be in the range of 26-35 percent (the saturation point of the wood fibers).

To steam wood for bending at home, use home-made cylindrical chambers made of metal / polymer pipes or rectangular wooden boxes. Heating tanks act as a source of steam, electric kettles and other similar devices that can provide a temperature of about 105 degrees and a little pressure. This is always followed by the stage of drying the part (+ exposure of the fixed form) to about fifteen percent and its finishing.

Chemical methods of plasticizing wood

It is also known that it is possible to make lumber more pliable using impregnation with various compositions. There are ready-made impregnations that make wood cells more plastic, for example, Super-Soft 2. Some practitioners soak wood in so-called textile conditioners, with similar results.

But rather primitive “recipes” containing ammonia and ethyl alcohol, glycerin, alkalis, hydrogen peroxide, dissolved alum can also be used ... Many of them are extremely simple - they increase the ability of the workpiece to absorb water and help retain moisture in the fibers.

Thin products such as veneer are spray processed, but pre-treatment of normal lumber with chemicals is usually done by full immersion. It takes time for the working substances to get inside the bar or rail, usually it takes from 3-5 hours to several days (although heating helps to reduce the wait).

It is largely because of the duration of the processes that chemical plasticization is not often used, although there are other problems: the cost of chemistry, color changes, the need to provide protection from harmful fumes, the increased tendency of such curved parts to straighten ...

Tips for bending lumber using hydrothermal preparation

• Very carefully select the quality of the workpiece for bending. It is better not to use material with cracks, knots (even live and intergrown), fiber inclination. If there are no options for this, then orient the part in the bending fixture (machine or template) so that the defects fall into the concave radius zone, and not into the tension zone on the outer radius. Give preference to the bending method with a bar.
• When selecting a workpiece, it is imperative to provide for a change in the size of the part after molding. For example, the thickness of a coniferous bar can be reduced by 30 percent if bending with pressing is performed.
• Even if you are planning an extensive finishing- do not leave too much material. How thinner workpiece, the easier it bends without breaking.
• If the amount of work is small, then it is better not to cut out blanks, but to prick them from chocks. So it is possible to avoid cutting the fibers and, as a result, marriage during bending.
• For bending, it is desirable to use lumber with natural moisture. If dry blanks are used, then preference should be given to those that have not been processed in drying chamber, but dried under a canopy - in an atmospheric way.
• After steaming, work with softened wood very quickly, as lignin begins to harden almost immediately, especially in the most vulnerable outer layers of solid wood. Usually you need to focus on a margin of time from half an hour to 40 minutes, so there is no point in making large cameras if you simply do not have time to install all the material from which into templates.
• Position the material in the steam chamber so that it is the surfaces facing the outer radius that are unobstructed by the steam jets.
• To save time, many carpenters forgo the use of clamp templates. Instead, they use metal staples and wedges, or limit posts, on the templates.
• Keep in mind that a curved bar or rail will still tend to straighten. And this straightening always occurs by a few percent. So when required high accuracy in the manufacture of the part, it is necessary to conduct tests and, based on the results obtained, correct the shape of the template (reduce the radius).
• After cooling the part in the form, let it stand for a while. Some experienced furniture makers prefer to make an exposure of 5-7 days. The tire, as a rule, is left fixed to the part for all this time.

Nature does not like straight lines and it takes a lot of time and effort to make wooden crafts straight. However, wood bending is also a rather laborious process. bent wooden elements often used in Scandinavian furniture in the form of beautiful, light and durable products with a unity of structure and form. In this article, we will look at several ways to bend wood: simple power bending, kerf bending, pair bending, and layer bending.

This is the simplest method and consists of manually bending the wood and attaching it to a mold to fix the bend. The thinner the wood, the easier it is to bend. It follows from this that the greater the bend, the thinner the wood should be. The veneer can acquire almost any bend, while an oak blank 2 cm thick is almost impossible to bend. It should also be taken into account that different breeds woods have different degrees of flexibility. So the ratio of the thickness of the workpiece and the minimum bending radius for some species will be: beech - 1/2.5; oak - 1/4; birch - 1/5.7; alder - 1/8; spruce - 1/10; pine - 1/11. That is, with a beech blank thickness of 10 mm, the minimum bending radius will be 25 mm.

As a rule, the workpiece is fixed with glue, since the use of nails or screws in the bends can lead to cracks and breaks. There is an unspoken rule - what can be fixed by hand can also be fixed with glue. When gluing, to reduce gaps, you need to move from the center to the edges, or from one edge to the other.

This method of bending wood is the least durable, since the wood is sawn through almost its entire thickness and there is very little strength left in it. Therefore, this method of bending wood is used only where there is no heavy load, such as rounded corners, etc.

The main material for the manufacture of bent sawn parts is plywood. For best results, cuts are best made on circular saw using a limit stop. Cuts should be made across the fibers at a distance of about 5-10 mm. from each other. The depth of cut should be about 1/5 of the thickness of the workpiece.

To fix the bend, you can use glue or wood filler. By gluing and fixing two curved slats with cuts inward, you can create interesting elements in some designs, albeit with limited strength.

By their own physical properties such wood is close to hydrothermally bent wood, and according to some indicators of dynamic loads, it has even better mechanical properties than solid wood.

The first step is to prepare the slats. The thickness of the lamellas is largely determined by the magnitude of the bend. The greater the bend, the thinner the lamellas should be and vice versa. As a rule, the thickness of the lamellas should not exceed 3.2 mm.

Then the cut layers of wood are smeared with glue and compressed in a template using grippers. To connect the lamellas, you cannot use ordinary carpentry glue. For these purposes, adhesives based on urea-formaldehyde or epoxy resins are best suited.

Before removing the part from the template, the glue should set for a day. It should also be borne in mind that after unclenching the mold, the workpiece may straighten a little. This effect can be minimized by reducing the thickness of the lamellas or creating a shape with a slight inflection.

Hydrothermal bending of wood gives the highest quality result, but requires a lot of labor and technical equipment.

Before starting the bending process, due attention should be paid to the choice of wood. Almost any type of wood can be bent, but hardwoods such as oak, beech, elm, birch, cherry, maple, walnut, ash have the best flexibility. It is not recommended to use coniferous and softwoods such as spruce, pine, cedar, alder. It is also important that the wood is free from cracks and knots at the intended bend.

Each cell of wood fibers is covered with lignin - glue-like chemical, which at ordinary temperature firmly binds the fibers. The heat transferred from the steam softens the lignin, allowing the fibers to contract and stretch. As the lignin cools, it hardens and binds the fibers together again.

Freshly cut wood is best suited for bending. The best option atmospheric drying wood is also, since during chamber drying, lignin is noticeably strengthened, making it difficult to bend. Before steaming, kiln-dried wood can be soaked overnight in water. Atmospheric wood and pre-soaked kiln-dried wood require the same processing time.

Wood acquires the best plastic properties at a moisture content of 25-30% and at a temperature of about 100°C. Steaming time depends on the thickness of the wood. So, for example, for steaming a workpiece with an initial moisture content of 30% and a thickness of 25 mm to reach a temperature in the center of the workpiece up to 100°C, it takes 1 hour, and about 2 hours with a thickness of 35 mm.

Before removing the workpiece, make sure that all tools are at hand, as the wood cools and hardens very quickly. Be sure to wear thick gloves to avoid getting burned by the steam. Remove the part and immediately fix it with grippers.

The removal of the product from the mold is usually accompanied by a slight extension. Therefore, the shape must have a bend a little more than required in order to maintain the desired curvature of the product. To minimize buckling, leave the piece fixed in the mold for at least a few days.

In the manufacture of furniture, you can not do without curvilinear parts. You can get them in two ways - sawing and bending. Technologically, it would seem that it is easier to cut a curved part than to steam, bend and then withstand it for a certain time until it is fully ready. But sawing has a number of negative consequences.

Firstly, there is a high probability of cutting the fibers when working with a circle saw (it is used in this technology). The result of cutting the fibers will be the loss of strength of the part, and, as a result, of the entire product as a whole. Secondly, sawing technology involves a greater consumption of material than bending technology. This is obvious and no comment is required. Third - all curved surfaces sawn parts have end and half-end cut surfaces. This significantly affects the conditions for their further processing and finishing.

Bending avoids all these disadvantages. Of course, bending involves the presence of special equipment and fixtures, and this is not always possible. However, bending is possible in the home workshop. So, what is the technology of the bending process?

The technological process of manufacturing bent parts includes hydrothermal treatment, bending of blanks and their drying after bending.

Hydrothermal treatment improves the plastic properties of wood. Plasticity is understood as the property of a material to change its shape without destruction under the influence of external forces and keep it after the action of the forces is eliminated. Wood acquires the best plastic properties at a moisture content of 25 - 30% and a temperature in the center of the workpiece by the time of bending of about 100 ° C.

Hydrothermal treatment of wood is carried out by steaming in boilers with saturated steam. low pressure 0.02 - 0.05 MPa at a temperature of 102 - 105°C.

Since the duration of steaming is determined by the time it takes to reach the set temperature in the center of the steamed workpiece, the steaming time increases with increasing thickness of the workpiece. For example, for steaming a workpiece (with an initial humidity of 30% and an initial temperature of 25°C) with a thickness of 25 mm to reach a temperature in the center of the workpiece of 100°C, 1 hour is required, and a thickness of 35 mm - 1 hour and 50 minutes.

When bending, the workpiece is placed on a tire with stops (Fig. 1), then in a mechanical or hydraulic press, the workpiece together with the tire is bent to a given contour; in presses, as a rule, several workpieces are bent simultaneously. At the end of bending, the ends of the tires are pulled together with a coupler. The bent blanks are sent for drying along with the tires.

The workpieces are dried for 6-8 hours. During drying, the shape of the workpieces stabilizes. After drying, the blanks are freed from templates and tires and kept for at least 24 hours. After holding, the deviation of the dimensions of the bent blanks from the original ones is usually ± 3 mm. Next, the blanks are processed.

For bent blanks, peeled veneer, urea-formaldehyde resins KF-BZh, KF-Zh, KF-MG, M-70, particle boards P-1 and P-2 are used. The thickness of the workpiece can be from 4 to 30 mm. Blanks can have a wide variety of profiles: angular, arc-shaped, spherical, U-shaped, trapezoidal and trough-shaped (see Fig. 2). Such blanks are obtained by simultaneous bending and gluing together veneer sheets lubricated with glue, which are formed into packages (Fig. 3). This technology makes it possible to obtain products of a wide variety architectural forms. In addition, the production of bent glued parts from veneer is economically feasible due to the low consumption of timber and relatively low labor costs.

Layers of plots are smeared with glue, laid in a template and pressed in (Fig. 4). After exposure under the press until the glue has completely set, the knot retains the shape given to it. Bent glued knots are made from veneer, from hardwood and coniferous plates, from plywood. In bent glued veneer elements, the direction of the fibers in the veneer layers can be either mutually perpendicular or the same. The bend in the veneer, in which the grain of the wood remains straight, is called a bend across the grain, and in which the grain is bent, it is called a bend along the grain.

When constructing bent glued veneer assemblies that carry significant loads during operation (legs of chairs, cabinet products), the most rational designs are those with a bend along the fibers in all layers. The rigidity of such knots is much higher than knots with mutually perpendicular direction of wood fibers. With a mutually perpendicular direction of the veneer fibers in the layers, bent glued knots up to 10 mm thick are designed that do not carry heavy loads during operation (walls of boxes, etc.). In this case, they are less susceptible to form change. The outer layer of such knots should have a fractional direction of the fibers (bending along the fibers), since when bending across the fibers, small fractional cracks appear at the bending points, which exclude good finish products.

Permissible (curvature radii of curved veneer elements depend on the following design parameters: veneer thickness, number of veneer layers in a package, package design, billet bending angle, mold design.

In the manufacture of bent profile units with longitudinal cuts, it is necessary to take into account the dependence of the thickness of the bent elements on the type of wood and the thickness of the bent part.

In the tables, the elements remaining after the cuts are called extreme, the rest - intermediate. Minimum distance between the cuts that can be obtained is about 1.5 mm.

With an increase in the bending radius of the plate, the distance between the cuts decreases (Fig. 5). The width of the cut depends on the bending radius of the board and the number of cuts. To obtain rounded nodes, in the slab, after veneering and grinding, a groove is selected in the place where the bend will be. The groove can be rectangular or dovetail. The thickness of the remaining plywood bridge (the bottom of the groove) should be equal to the thickness of the facing plywood with an allowance of 1-1.5 mm. A rounded bar is inserted into the rectangular groove with glue, and a strip of veneer is inserted into the dovetail groove. Then the plate is bent and kept in the template until the glue sets. To give the corner greater strength in it with inside you can put a wooden square.