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

This is the simplest method and involves bending wood by hand and attaching it to a mold to secure 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. Veneer can take on almost any bend, while an oak blank 2 cm thick is almost impossible to bend. It should also be taken into account that different types of wood 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 bending areas can lead to the formation of 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 because the wood is sawed through almost the entire thickness and very little strength remains in it. Therefore, this method of bending wood is used only where there is no heavy load, for example rounded corners, etc.

The main material for the manufacture of bent-sawn parts is plywood. To achieve best results It is better to make cuts on a circular saw using a limit stop. The cuts should be made across the grain at a distance of about 5-10 mm. from each other. The depth of the cut should be about 1/5 of the thickness of the workpiece.

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

In terms of its physical properties, such wood is close to hydrothermally bent wood, and in terms of some indicators of dynamic loads, it has even better mechanical properties, rather than solid wood.

The first step is to prepare the slats. The thickness of the lamellas is largely determined by the amount of bending. 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.

The cut layers of wood are then coated with glue and pressed into the template using grippers. You cannot use regular wood glue to connect the slats. 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 within 24 hours. It should also be taken into account that after the mold is released, the workpiece may straighten out a little. This effect can be minimized by reducing the thickness of the lamellas or creating a shape with a slight bend.

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

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

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

Freshly cut wood is best suited for bending. The best option is also atmospheric drying wood, since during chamber drying lignin is noticeably strengthened, making bending more difficult. Before steaming the wood chamber drying can be soaked overnight in water. Processing of atmospheric-dried wood and pre-soaked kiln-dried wood requires the same amount of time.

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

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 secure it with the grips.

Removal of the product from the mold is usually accompanied by a slight bending. Therefore, the form must have a bend a little more than required in order to maintain the desired curvature of the product. To minimize deflection, leave the part secured in the mold, while at least, for a few days.

Instructions

To manufacture curved parts from wood, two main methods are used: sawing according to a template and bending pre-steamed wood using a template on a special machine. The first method leads to cutting the fibers and reducing the strength of the parts. Bending provides a high percentage of useful yield of parts and significant strength. Bent parts can be finished with high quality and subjected to various mechanical treatments (profiled, formed with spikes, eyes, etc.).

Ability wooden board bendability is determined by the plasticity of the wood and depends on the type of wood. Beech, birch, oak, pine and spruce have the greatest plasticity. But you can control the plastic properties of the workpiece by hydrolyzing it heat treatment.

At a temperature of 100°C and a humidity of 30%, part of the substances that make up the cells of the material goes into a gel state, while the cell walls and wood fibers become elastic and soft. This wood bends easily. After drying bent board retains its given shape as colloidal substances harden.

Processing the workpiece consists of boiling it in hot water or steaming with saturated low pressure steam. Steaming is more common, since with this treatment the wood is heated more evenly and the wood does not become excessively moistened.

When a board treated in this way is bent on a pattern or in a special clamping device, internal stresses arise in the material. Wood stretches on the convex side and contracts on the concave side. In the middle neutral layer the voltages are zero.

The outer layer will become elongated under the action of tensile stresses, and the inner layer will become shorter. The amount of deformation depends on the thickness of the dock and the bending radius. To limit the elongation of wood fibers and prevent their possible rupture, a special steel bus with a thickness of up to 2.5 mm is applied to the convex side of the bent part. The workpiece is bent together with the tire. In this case, the neutral line extends towards the stretched fibers beyond the board, and bending occurs only due to compression.

When making a wide variety of joinery products, the craftsman often has to use curved parts. It is not always possible to obtain the required shape by sawing, since ensuring the strength of the material and its economy are important here. In such cases, it is necessary to bend the wood under different angles.

You will need

• - hot water;
• - open fire;
• - sample;
• - steel strip;
• - ammonia water.

Instructions

Use steaming or heat treatment for bending. If you expose the wood for several hours to high temperature and moisture, you can achieve a change in the plasticity of the material and bend the workpiece at the required angle.

Carefully select the ones you will subsequently bend. Use boards sawn lengthwise for this treatment. Avoid defective and twisted boards, as well as those workpieces that have knots. If you use materials with damaged fibers, the workpiece may crack at the location of the defect.

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

Often during the process repair work There is a need to obtain curved surfaces of products made from wood. How to bend a board so that the bend is strong and does not crack during the bending process? Well, if you have already decided to do major renovation with your own hands, then you should not retreat in the face of such difficulties. In this article we will talk in detail about how to give wood material a curved shape.

How to bend a tree?

No, our task is not at all to bend an innocent plant. We are talking about wood building materials. How to bend a tree so that it bends and does not break? Bending method wooden products known since ancient times: to give wood a shape, only heat and moisture are needed, under the influence of which the plasticity of the material increases with all the ensuing consequences. How to bend a tree? Keep it in hot water ( the higher the temperature, the faster the processes occur) or steam ( a steam generator can be made from a kettle or use an iron). The higher the temperature, the faster the wood yields and you can start bending it. Moistened and heated wood can be bent under the influence of a load (the ends of the board are placed on supports), and a 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 wood, we can dwell on this issue in more detail.

Reaction of wood to external influences

The fact is that wood reacts differently to bending. The convex part is subject to tension, the concave part is subject to compression. Moreover, the material also reacts differently to steaming. For example, the ability to compress increases by as much as a third, but the ability to stretch - just a couple of percent. That’s why you shouldn’t think about how to bend a board more than two centimeters thick at home. It is also necessary to take into account that different types wood reacts differently to bending. For example, species such as oak, larch, and maple bend poorly, but beech, ash, and walnut bend 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 humidity, then ironing it (an iron is required), and fixing it in a template. Any frame element can serve as a template and its shape does not necessarily have to be curvilinear. The product is attached to the template using tape. Can be clamped bent plywood between two spacers, give it a bent shape using ropes, tying them around the product in several places along the radius of curvature. Plywood can only be used after it has dried. It seems like we’ve figured out how to bend plywood – let’s 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 two ways: either bend thin sheets (no more than 5 mm) and glue them together, or use flexible MDF. in which there are transverse slots on one side. The thickness of such sheets is usually 8 mm. When bending, they are placed on top of each other with their milled sides, and then glued together. That's all!

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If there is a need to develop a curved element made of wood, then most likely you will encounter a number of difficulties. At first glance, it will seem that cutting out the required element in a curved form will be easier, but in this option, the wood fibers will be cut and weaken the reliability of the part. Plus, during execution there is a very large consumption of material.

Stages of work on bending boards 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: durable and reliable material from wood for the manufacture of all kinds of products can only be obtained under the conditions that the wood is perfectly dried. However, changing the shape of dry wood is a rather labor-intensive process, since dry wood can easily break.

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

Specifics of working with wood

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

Can bend timber blanks made from laminated and solid wood. Plus, to give the desired shape, peeled and planed veneer is used. Hardwood is considered the most ductile. 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 the workpiece is steamed, its ability to compress significantly increases, specifically by a third, while the ability to stretch increases by only a few percent. Thanks to this, you can’t even think about bend tree thicker than 2 cm.

How bend board in artisanal conditions: heating in a 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. There must be a hole in it that is designed for steam to escape. Otherwise, an explosion may occur under pressure.

This hole should be located in the bottom of the box. Plus, in the box you need to calculate a removable lid through which you can remove bent wood, as soon as it receives the required form. In order to hold the bent wood blank in the required shape, it is necessary to use special clamps. They can be made independently from wood or purchased at a building materials store.

Several round scraps are made from wood. Holes are drilled in them, offset from the center. After this, you need to push the bolts through them, and then drill another through the sides to push them in firmly. Such simple crafts can perfectly serve as clamps.

Now you can start steaming the wood. To do this you need to close wood preparation in the steam box and worry about the heat source. For every 2.5 cm of product thickness, the time spent on steaming will be approximately an hour. After its expiration, the tree should be removed from the box and given the required shape by bending it. The process should be performed quickly enough, and the bending itself should be done gently and carefully.

Tip: Due to varying degrees of flexibility, some types of wood will bend more easily than others. Any method requires the application of varying amounts of force.

As soon as the result you want is achieved, the bent workpiece must be secured in this position. Fastening a tree is possible during the process of its development new form, making it easier to control the process.

How bend board in artisanal conditions using chemical impregnation

Since lignin is responsible for the stability of wood, its bonds with the fibers must be broken. This is achieved chemically, and it is quite possible to do this in artisanal conditions. Best suited for such purposes ammonia. The workpiece is soaked in 25% aqueous solution ammonia, which significantly increases its plasticity. Likewise, it will be possible bend, twist it or squeeze out some relief shapes under pressure.

Advice: 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. Soaking of wood 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 shape, but also to evaporate the ammonia. However, bent wood must be left in a ventilated area. It is noteworthy that when the ammonia has evaporated, the wood fibers will acquire the same reliability as before, which will enable the workpiece to retain its own shape!

How bend board in artisanal conditions: layering method

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

The boards must be cut with a straight edge, and not at all front side. Likewise, they can be put together with the least amount of change. A layer of cork is applied to the mold, which can help avoid any unevenness in the shape of the saw and will provide the opportunity to make a more even bend. Plus, the cork will prevent delamination in the mold. After that, glue is applied to the upper side of one of the lamellas with a roller.

It is best to use urea-formaldehyde glue, consisting of two parts. It has a high level of adhesion, but takes a long time to dry. You can also apply resin to epoxy based, but such a composition will cost a lot of money, and absolutely not everyone can afford it. The standard version of wood glue is not suitable for this type of application. Although it will dry quickly, it is considered too soft, which is not at all welcome in this option.

Product from bent wood need to fit into the mold as quickly as possible. So, another one is placed on the lamella coated with glue. The process must be repeated until the bent workpiece reaches the required thickness. The boards are fixed together. After the glue has completely dried, it is necessary to shorten it to the required length.

How bend board in artisanal conditions: cut through

The prepared piece of wood needs to be sawn through. The cuts are calculated at 2/3 of the thickness of the workpiece. They must be located inside the bend. You need to be very careful, as rough cuts can easily deform the tree and even completely break it.

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

The cuts are made across the grain of the wood. Afterwards you need to compress the edges of the workpiece, which will make it possible to combine the resulting cracks into a single whole. This is the shape the bend takes upon completion of the work. After which he is corrected. In many cases, the outer side is finished with veneer, less often with laminate. This impact will give you the opportunity to correct the bend and hide almost any defects made during manufacturing. Gaps in bent tree they are hidden quite easily - for this, sawdust and glue are mixed, after which the gaps are filled with the mixture.

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

So, using such tips you can without big problems bend wood with your own hands.

The layers are carefully lubricated with glue, placed in a template and pressed into place. Bent glued units made from veneer, from hardwood and softwood boards, from plywood. In bent-laminated veneer elements, the direction of the fibers in the veneer layers can be either mutually perpendicular or identical.

When manufacturing 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.

As the bending radius of the slab increases, the distance between the cuts decreases, as can be seen in the figure above. That is, the width of the cut directly depends on the bending radius of the slab and the number of cuts.

Now let's look at the theoretical aspects of bending

Curved solid wood parts can be made in two basic ways:

cutting out curved workpieces and giving a straight bar a curved shape by bending it on a template. Both methods are used in practice and have their advantages and disadvantages.

Sawing curved blanks The technology is simple and does not require special equipment. However, when sawing, the wood fibers are inevitably cut, and this weakens the strength so much that parts with large curvature and a closed contour have to be made up of several elements by gluing. On curved surfaces half-end and end surfaces of cuts are obtained and, in connection with this, the processing conditions on milling machines and finishing. In addition, when cutting it turns out large number a large amount of waste. The production of curved parts using the bending method requires, compared to sawing, a more complex process. technological process and equipment. However, when bending, the strength of the parts is completely preserved and even in some cases increases; end surfaces are not created on their faces, and the modes of subsequent processing of bent parts do not differ from the modes of processing straight parts.

Element bending
A- nature of the workpiece deformation during bending;
6 - bending the workpiece with the tire according to the template:
1 - template; 2 - notches; 3 - pressing roller; 4 - tire

When the workpiece is bent within the limits of elastic deformations, stresses normal to the cross section arise: tensile on the convex side and compressive on the concave side. Between the zones of tension and compression there is a neutral layer, the normal stresses in which are small. Since the value normal stress changes across the cross-section, shear stresses arise, tending to move some layers of the part relative to others. Since this shift is impossible, bending is accompanied by stretching of the material on the convex side of the part and compression on the concave side.

The magnitude of the resulting tensile and compressive deformations depends on the thickness of the bar and the bending radius. Let us assume that the block rectangular section bent in a circular arc and that the deformations in the bar are directly proportional to the stresses, and the neutral layer is located in the middle of the bar.

Let us denote the thickness of the bar H, its initial length through Lo, bend radius along the neutral line through R(Fig. 60, a). The length of the block along the neutral line when bending will remain unchanged and is equal to Lo = p R( j /180) , (84) where p is the number pi(3, 14...), j - bend angle in degrees.
The outer stretched layer will receive elongation D L (delta L). Total length the stretched part of the block is determined from the expression Lo+ D L= p (R + H/2) j /180 (85)
Subtracting the previous one from this equation, we obtain the absolute elongation
D L= p (H/2)( j /180). (86)
Elongation Er will be equal to D L/Lo = H/2R, i.e. relative elongation when bending D Ll/Lo depends on the ratio of the thickness of the bar to the bending radius; the thicker the block, the larger it is H and the smaller the bend radius R. A similar relationship for the value of relative compression during bending can be obtained in a similar way.
Let's assume that around the pattern R" bent block with initial length Lo and at the same time maximum compressive and tensile deformations are achieved. Designated by E szh the value of permissible compressive deformation of wood along the fibers, and through E grow the value of the permissible tensile strain along the fibers, we can write a relationship for the stretched side
L = Lo(1 + Erast)= p (R" + H) j /180 (87)
From here R" + H = / p ( j /180) .
For the compressed (concave) side there will be L 2 = Lo (1 - Eczh) = p R"(j/180)
or R" = / p ( j /180 ). (88)
Subtracting the second from the first expression, we get
H = )