When making furniture, you cannot do without curved parts. You can get them in two ways - sawing and bending. Technologically, it would seem easier to cut out a curved part than to steam, bend and then hold it for a certain time until it is completely ready. But sawing has a number of negative consequences.

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

Bending allows you to avoid all these disadvantages. Of course, bending requires the presence of special equipment and devices, and this is not always possible. However, bending is also possible in a home workshop. So, what is the technology of the bending process?

The technological process for 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 to retain it after the action of the forces is eliminated. Wood acquires its best plastic properties at a humidity of 25 - 30% and a temperature in the center of the workpiece at the time of bending of approximately 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 set temperature in the center of the steamed workpiece, then the steaming time increases with increasing thickness of the workpiece. For example, to steam a workpiece (with an initial humidity of 30% and an initial temperature of 25 ° C) with a thickness of 25 mm to achieve a temperature in the center of the workpiece of 100 ° C, 1 hour is required, with a thickness of 35 mm - 1 hour 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 tightened with a tie. The bent workpieces are sent for drying along with the tires.

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

For bent blanks, peeled veneer, urea-formaldehyde resins KF-BZh, KF-Zh, KF-MG, M-70, and 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: corner, arc-shaped, spherical, U-shaped, trapezoidal and trough-shaped (see Fig. 2). Such blanks are obtained by simultaneously bending and gluing together veneer sheets coated with glue, which are formed into packages (Fig. 3). This technology makes it possible to obtain products of a wide variety of architectural forms. In addition, the production of bent-laminated veneer parts is economically feasible due to the low consumption of timber and relatively low labor costs.

Layers of plots are smeared with glue, placed in a template and pressed into place (Fig. 4). After exposure under the press until the glue has completely set, the assembly retains its given shape. Bent-glued units are made from veneer, from hardwood and softwood plates, and from plywood. In bent-laminated veneer elements, the direction of the fibers in the veneer layers can be either mutually perpendicular or identical. Bending of veneer, in which the wood fibers remain straight, is called bending across the grain, and in which the fibers bend, bending along the grain.

When designing bent-laminated veneer units that bear significant loads during operation (chair legs, cabinet products), the most rational designs are those with bending along the fibers in all layers. The rigidity of such knots is much higher than knots with mutually perpendicular directions of wood fibers. With the mutually perpendicular direction of the veneer fibers in the layers, bent-glued units up to 10 mm thick are constructed, which do not bear large loads during operation (box walls, etc.). In this case, they are less susceptible to change in shape. The outer layer of such units must have a lobar direction of the fibers (bending along the fibers), since when bending across the fibers, small lobar cracks appear at the bending points, which exclude good finish products.

Acceptable (radii of curvature of bent-laminated veneer elements depend on the following design parameters: veneer thickness, number of veneer layers in the package, package design, bending angle of the workpiece, mold design.

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.

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

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

Wood is recognized as one of the safest materials for human health used in construction and in the manufacture of various furniture. Its environmental friendliness can be rated five points, which significantly expands the scope of use wooden products. Wood can be used to produce workpieces of various shapes and sizes. Special ones help with this. These technologies also include wood bending and gluing, which is widely used in the modern production cycle.

The entire woodworking process takes a significant amount of time. First the wood - all this happens in wood processing enterprises. Subsequently, boards and other materials are prepared from wood.

These blanks are sent to factories, where they are specially made from them. building materials or various furniture. During the production process, wooden blanks of different shapes and sizes may be required, and therefore woodworking techniques such as bending and gluing are widely used.

Bonding is used to produce parts of the desired size and shape. Wood splicing can be done by width, length or thickness. Pre-prepared ends of the workpieces can have special grooves or tenons, which increases the strength of the parts being connected. Different types of wood glue are used in the gluing process.

Wood bending is necessary to produce curved parts. You can bend wood manually, subject to certain features of this work, or special machines.

The strength and practicality of wooden products, for the manufacture of which special machines for gluing or bending are used, can be rated at five points. Woodworking factories always try to follow all the technology for working with wood, and therefore the goods produced are of high quality.

Photos of the wood processing methods described above

Splicing Gluing Bending

Main stages of gluing technology

Gluing is the main process of working with wood in any furniture production. In order to obtain a durable and high-quality workpiece, it is necessary to strictly adhere to the entire technology of the process of connecting individual parts. The accuracy of all work is also necessary to prevent possible subsequent deformation.

The process of joining wood and products made from it consists of several stages:

• Preparation of the blanks themselves.
• Selection and application of adhesive composition.
• Actually the gluing itself.

Preliminary preparation of wooden blocks and other workpieces consists of creating special tenons or grooves in them, which can be done using special tool– cutters.

Using a cutter to join wood

Milling is a fairly old branch of wood processing. The first milling machines appeared more than three centuries ago. Today, milling is an indispensable and universal method of wood processing.

For this woodworking machine, you can choose cutters of different shapes - sharpened elements with different types of blades. Using these cutters, various parts are made.

In the gluing process, milling machines are necessary for:

• Cutting tenons of different shapes, with the help of which individual workpieces will be glued together in the future.
• Creating holes in the material. Creating folds and grooves, which are also necessary in the process of manufacturing parts of different shapes.

Milling machines are used everywhere, they can be either manual or electric. The ease of making wooden blanks for gluing using a machine can be rated four points. In order to obtain an accurate workpiece, you first need to gain some experience.

This video provides an overview of cutters for splicing wood and making technological connections. Shown are cutters for straight and angular splicing, as well as a microtenon, zigzag and wave cutter:

Automatic line for wooden blanks

Splicing lumber in any production allows you to create high-strength materials with new, sought-after qualities and also allows you to rationally manage production waste.

Automatic splicing lines include several sequentially operating machines, which allow you to ultimately obtain the material of the required length and width from short blanks. With the help of a splicing line, glued laminated timber, which is popular today, is produced.

The entire technological process when using a production line for splicing wooden blanks consists of several stages, which are provided by a complex of machines included in the installation:

• The cutting press machine provides required sizes material.
• A router prepares tenons and grooves in wood pieces.
• The gluing installation distributes the glue in accordance with the set parameters.
• The cross-cutting machine completes the gluing process.

Using a splice line on furniture factories provides high performance, reduces the number of jobs. , obtained using automatic machines, can be rated five points, since the entire process is strictly controlled.

This is how an automatic length splicing line works:

Types of glue

The correct selection of the type of glue determines the quality of joining wooden workpieces. The choice of glue also depends on the type of wood being glued and the shape of the workpieces. Waterproof adhesive compositions are most often used.

The furniture industry uses several types of synthetic adhesives:

• Thermosetting adhesives are used for gluing tenon parts without heating. The basis of these types of glue are liquid resins.
• Phenol-formaldehyde adhesives are used for gluing wood boards, wooden blanks and plywood.
• Epoxy adhesives are mainly used for joining wood with other materials - metal, plastic.
• At woodworking enterprises, glue based on urea resins is most often used. Also often used adhesive compositions in powder form, which require preliminary preparation.

Bonding of parts is carried out coldly and by heating them. To glue workpieces along the edges, adhesive film is often used; it comes in sheets of various sizes.

Before gluing, the parts must first be prepared, that is, degreased, removed dirt and various types spots After applying glue over the entire surface and connecting the required workpieces, the parts are clamped using special devices, which are removed only when completely dry.

Machine tools

To splice glued wood, special machines in the form of presses can be used. They clamp the parts for the required time. This ensures a strong connection between the adhesive surfaces and prevents movement of parts. The press can be selected according to the length of the beam, power, and the presence of additional functions.

Gluing wood at home

Wood gluing may sometimes be necessary at home. This often happens when wooden furniture sets are put up or when there are various breakdowns. Before gluing, the surfaces of wooden products must be properly prepared.

To do this, their pores are cleaned of old glue and paint layers, degreased with a solvent, and dried. After applying glue to both parts, they are carefully connected and clamped in a clamp for at least 30 minutes.

Commonly used adhesives include:

• Casein glue.
• Waterproof seams are provided by synthetic wood glue.
• Strong bonding is obtained when using glue “Dubok”, “Ago”, “Mekol”, “Mars”.

In order to achieve high strength of the parts to be glued, it is necessary to strictly follow the instructions included with each type of glue.

You can clearly see how wood is glued together in the video:

Bending technology

Wood bending can be defined as the process of bending layered or solid pieces of wood to give them the desired curved shape. Bending technology is based on plastic qualities different types wood Curvilinear wooden parts can also be obtained by processing on special machines, but this method is rarely used, as it is endowed with a number of negative consequences.

Process Description

Hardwood such as oak, beech, and ash has greater plasticity. Therefore, mainly the species of these trees are used for the manufacture of curved parts. There are cold and hot bending of wood.

Hot bending is based on a sharp increase in the plasticity of wooden blanks when they are heated from 80 to 120 degrees. This heating mode is achieved by boiling in water or steaming.

The wooden blanks plasticized in this way are bent according to the prepared template and secured with clamps, after which they are cooled and dried. When bending, the convex side is stretched to the required level, and the concave side is compressed. Thick workpieces are bent using special machines.

Cold bending is used to produce multilayer curved bent parts. To obtain a part of the desired shape, you need to place several blanks coated with glue on top of each other, give them the required shape and, using a press machine, wait the required time. The shape of blanks obtained by cold bending is retained longer.

This video will tell you how curved wood is made:

Bending wood at home

Wood bending at home begins with the choice of material. The prepared parts must be straight-layered; they must first be dried under natural conditions. You also need to soak parts if they are made of ash, oak, or beech. Before bending, the workpieces must be steamed.

To do this, you can use a steam chamber prepared yourself. To make such a device, a pipe and a boiling kettle are suitable, from which steam will continuously flow into this chamber through hoses.

The holding time of the blanks can only be determined experimentally, but it is believed that in order to achieve the required plasticity, it is necessary that one centimeter of wood in thickness be steamed for 30 to 40 minutes. It is also not worth overexposing the product.

Before you start bending, you need to prepare the mold and clamps. After heating the wood, it can be bent well only for 5-10 minutes, so everything needs to be done extremely quickly. The products are kept in the mold until they are completely dry, usually this takes at least one week. The finished part can then be machined or processed.

They use this wood processing process to make different types of furniture with their own hands. At the same time, the price of the products is significantly reduced and this can be rated five points. But the labor intensity of the entire process takes a lot of time, and therefore only truly passionate people can take up bending wooden blanks and their subsequent use.

Examples of interior elements made from bent wood

Headboard Rocking chair Table Decorative element Chairs

Bending wood using steam. Or how to bend strong, unbending oak into the shape you need without any problems.

I have been working with flexible wood for 13 years now and during this time I have built many steaming chambers and tested different steam generation systems in action. What you are reading now is based on reading literature and personal practical experience. Even mostly from experience. I usually worked with oak and mahogany (mahogany). I had to deal a little with thin birch veneer. I haven’t tried other breeds because I build and repair boats. Therefore, I cannot judge with authority the work with other species such as cedar, pine, poplar, etc. And since I haven’t done this myself, I can’t judge it. I write here only about what I experienced personally, and not just what I read in a book.

After this introduction, let's get down to business...

To begin with, there are a few basic rules that are always followed.

By steaming wood to bend it, you soften the hemicellulose. Cellulose is a polymer that behaves like thermoplastic resins. (Thanks to John MacKenzie for the last two suggestions).

To do this, you need heat and steam at the same time. I know that in Asia people bend wood over a fire, but that wood is definitely quite wet - usually freshly cut. Shipbuilders in ancient Scandinavia prepared hull materials for their ships and placed them in a saltwater swamp so that they would remain flexible until they were ready for use. However, we are not always able to obtain freshly harvested wood for these purposes, and excellent results can be achieved by using conventional air-dried wood. It would be very good if, a few days before the operation itself, you immerse the workpieces in water so that they gain moisture - those Vikings knew what they were doing. You need warmth and you need moisture.

The main rule concerns steaming time: one hour for every inch of wood thickness.

As I discovered, along with the probability of understeaming the workpiece, there is also the probability of oversteaming it. If you hovered an inch board for an hour and when you tried to bend it, it cracked, do not conclude that the time was not enough. There are other influencing factors that explain this, but we'll get to those later. Steaming the same workpiece for a longer time will not give a positive result. In such a situation, it’s a good idea to have a workpiece of the same thickness as that intended for bending and which you don’t mind. Preferably from the same board. They need to be steamed together and after the supposedly required time, take out a test sample and try to bend it into shape. If it cracks, then let the main workpiece steam for another ten minutes. But no more.

Wood:

As a rule, the best option it will if you can find freshly cut wood. I understand that the cabinet makers will shudder at these words. But the fact remains that fresh wood bends better than dry wood. I can take a six-foot-long plank of white oak, clamp one end of it in the workbench, and bend it to whatever curvature I need—that's how malleable the fresh wood is. However, naturally, it will not remain in this state and you will still have to float it.

In shipbuilding, the main evil is rot. If you are concerned about this issue, then please note that the very fact of steaming fresh wood eliminates its tendency to rot. Therefore, you don’t have to worry - the frames of boats are usually made from fresh steam-bent oak and do not rot if it is taken care of. This also means that in this way it is possible to make at least blanks for the Windsor Chair. However, I also worked a lot with air-dried oak and the result was also excellent.

When selecting wood for bending, one thing to avoid is cross-layering. When trying to bend such a workpiece may burst.

Therefore, regarding wood moisture content, the rules are as follows:

• Fresh wood is best.
• Air-dried wood is a second good option.
• Wood after drying is the third and very far from the first two option.

If all you have is from the dryer and you can’t get anything else - well, then you have no choice. I dealt with this too. But still, if you can get air-dried wood, it will be much better. Just last week I bent 20mm thick walnut boards for the transom of my yacht. The blanks were dried for several years and their bending went completely smoothly.

Steaming chambers.

It is absolutely useless, and even harmful for the bending result, to strive to make an absolutely sealed chamber. The steam must leave it. If you do not provide steam flow through the chamber, you will not be able to bend the workpiece and the result will be as if you steamed it for only five minutes. After all my experiences, this is familiar to me.

Cameras come in a variety of shapes and sizes. It should be large enough so that the workpiece seems to be suspended and steam flows around all sides of it. A good result will come from pine boards with a cross-section of about 50 x 200. One way to ensure the “hanging” of the workpiece is to drill through holes in the side walls of the chamber and drive round wooden rods from hardwood into it. With their help, the workpiece will not touch the bottom and the area of ​​​​closed wood will be minimal. However, you should not make the chamber so large that the amount of steam generated is not enough to fill its volume. The chamber should be such that it is humid inside and the steam rolls in waves. This means that the dimensions of the chamber must correspond to the capabilities of the steam generator (or vice versa).

When I needed to bend a five-meter mahogany board with a cross-section of about 200 x 20 for the new deckhouse of my yacht, I made a chamber from pine boards with a cross-section of 50 x 300. A 20-liter metal tank acted as a steam generator. The energy source was a propane torch. The thing is absolutely wonderful because it is convenient and mobile. Capacity 45000 BTU (1 BTU ~ 1 kJ). This is an aluminum cylinder with three legs and one burner with a diameter of 200 mm.

I recently found a 160,000 BTU propane burner in the West Marine catalog for $50 and purchased that as well. With its help I can bend frames even for "Constitution".

When I say one hour of steaming per inch of thickness, I mean one hour of SERIOUS CONTINUOUS steaming. Therefore, the boiler must be designed to provide steam for the required time. I used a new 20-liter fuel container for these purposes. Workpieces can only be placed into the chamber when the installation has reached full capacity and the chamber is completely filled with steam. We must absolutely ensure that the water does not run out prematurely. If this happens and you have to add water, it is better to give it up. Adding cold water will slow down steam generation.

One way to make the most of the water is to position the chamber at a slight angle so that the condensed water inside flows back into the boiler. But at the same time, it is necessary that the fitting through which the steam enters inside is closer to the far wall. Another way is to make a siphon system to ensure that its level is replenished as the water boils away.

Here's what a photo of such a system looks like:

In the picture you see a wooden camera located slightly at an angle. Directly below it is the steam generator boiler. They are connected to each other via a hose from the radiator. If you look closely, you can see an L-shaped pipe coming out of the base of the boiler on the left. It’s hard to see in the photo, but its vertical part is actually translucent and this way we will know about the water level inside the boiler. To the left of the boiler you can see a white bucket containing water for make-up. Take a closer look and you will notice a brown tube connecting the bucket to the vertical part of the pipe - the level gauge. Since the bucket is located on a hill, a siphon effect is observed: as the water level in the main boiler drops, water enters it from the bucket. You can add it from time to time, but do this extremely carefully so that it does not rush quickly into the boiler and cool it too much.

To minimize the need to add water during the steaming process, it is better to start work with a bucket filled to the top. I myself prefer to leave a small air gap in the boiler.

Many chambers have a door at the end through which workpieces can be moved if necessary and removed if necessary. For example, if you are engaged in the manufacture of bent frames and you would like to complete this as much as possible in a day, you melt the boiler and (when reaching full power) put the first workpiece inside. After 15 minutes, add the second one. After another 15 - the third and so on. When it's time for the first one, you take it out and bend it. I'm assuming this procedure will take less than 15 minutes. When she sits still, the second one is already on the way... etc. This allows you to get a lot of work done and avoid over-steaming.

The door has another important function. It doesn't even have to be made of hard material - on my small camera, just a hanging rag serves for this purpose. I say "hanging" because the steam must emanate outward from the end (since a stream of steam is needed). We must not allow what will happen in the cell overpressure, making it difficult for steam to enter. And besides, the picture itself wooden box, from which steam comes out in clouds, looks quite cool - passers-by are simply dumbfounded. The second purpose of the door is to prevent cold air from entering the chamber from below the workpieces.

So, we will assume that our wood is boiling (with a pleasant smell) and the templates are ready. Try to organize everything in such a way that the operation of removing the workpiece from the chamber and bending it goes quickly and smoothly. Time is of the essence here. You have only a few seconds to do this. As soon as the wood is ready, quickly take it out and immediately bend it. As fast as human dexterity allows. If pressing to the template takes time, just bend by hand (if possible). For the frames of my yacht (which have a double curvature), I took the blanks out of the chamber, stuck one end into the clamp and bent this end and then the other just by hand. Try to provide more bend than is necessary for the template, but not much. And only then attach it to the template.

But I repeat once again - the wood must be given curvature immediately - within the first five seconds. With every second the wood cools, it becomes less pliable.

The length of the blanks and the curvature at the ends.

It is practically impossible to produce blanks of exact length and expect to be able to achieve a bend at the ends. You simply don't have the strength to do it. For this reason, if you need a piece one meter long, but its thickness is more than 6 mm, you are better off cutting a piece about two meters long and bending it. I'm just going by the assumption that you don't have a hydraulic press in your workshop - I certainly don't have one myself. When cutting out a workpiece with a margin, remember that the shorter it is, the more difficult it will be to bend.
And if it is with a reserve, then the end of the real part will have a large curvature - an inch oak boards the last 150 mm are absolutely straight. Depending on the radius required at the end, it may be necessary to resort to wood carving in such areas and to take into account the required thickness when choosing the material.

Templates.

After steaming the workpiece and clamping it onto the template, you must wait a day for complete cooling. When the clamps are removed from the workpiece, it straightens somewhat. The extent of this depends on the structure and type of wood - it is difficult to say in advance. If the workpiece already has some natural bend in the desired direction, which can be taken advantage of (I try to do so whenever possible), the degree of straightening will be less. Therefore, if you require a certain curvature in the final product, the template must have more curvature.

How much bigger?

Here we are dealing with pure black magic and I personally cannot give you any numbers. One thing I know for sure: it is incomparably easier to straighten an excessively bent workpiece than to bend a cold, unbent one (provided that you do not have a giant lever).

Warning. If you bend workpieces for lamination, the template must be exactly the shape of the workpiece in the laminate - I have rarely had cases of large bending of well-bent laminated wood.

There are endless options for bending templates. And it doesn’t matter at all which one you choose if you happen to own a clamp factory - you can never have too many of them. If wood with a thickness of more than 12 mm is bent, the template must have significant mechanical strength - it will experience quite high loads. You can see what it looks like in the photo at the beginning of the article.
Quite often, when bending, people use a metal strip on the outside of the bend. This helps to distribute stress evenly along the length of the workpiece and avoid cracks. This is especially true if the outside fibers are located at an angle to the surface.

Well, that’s probably all my thoughts for now.

If there is a need to manufacture a curved wooden element, then at first glance it may seem that it is easier to cut out the required element in a curved form, but under such conditions the fibers of the wood material will be cut, thus weakening the strength of the part, and as a result, the entire product. In addition, when sawing, there is a huge waste of material, which cannot be said about the method, while the wooden blank is simply bent.

Wood is cellulose fibers bound together by a chemical called lignin. The flexibility of the tree depends on the placement of the fibers.

Only well-dried wood will be a reliable and durable source material for the production of various products. But the change of shape is dry wooden blank the process is complex, since dry wood can break, which is highly undesirable.

Having studied the technology of how to bend wood, and the fundamental physical properties of wood, which allow you to change its shape and then preserve it, you can fully engage in bending wood at home.

Some features of working with wood

Bending of wood is accompanied by its deformation, compression of the inner layers and stretching of the outer layers. It is not uncommon for tensile forces to cause the outer fibers to break. This can be prevented by preliminary hydrothermal treatment.

So, it is possible to bend blanks of timber made from solid and laminated wood. In addition, planed and peeled veneer is used for bending. The most plastic are hardwoods. These include beech, ash, birch, hornbeam, maple, oak, poplar, linden and alder. It is best to make bent glued blanks from birch veneer. It must be emphasized that in the total volume of bent-glued blanks, birch veneer occupies approximately 60%.

When steaming the workpiece, the compressive property increases significantly, namely by a third, while the tensile property increases by only a couple of percent. This means that one should not think a priori about whether it is possible to bend a tree thicker than 2 cm.

Steam box heating

First, go prepare the steam box. It may have been made by hand. Its main task is to hold the tree that needs to be bent. There should be a hole in it to allow the steam pressure to escape. Otherwise it will explode.

The steam outlet should be located in the bottom of the box. In addition, the box should have a removable lid through which it will be possible to pull out the bent wood after it has been purchased. the required form. In order to hold the bent wooden part in the desired shape, use clamps. You can make them yourself from wood or purchase them from specialty store.

It is necessary to make round trimmings from the wood - a couple of pieces. Off-center holes are drilled in them. Then you need to push the bolts through them, and after that drill another hole through the sides in order to push them in tightly. Such simple crafts can become excellent clips.

Now is the time to steam the wood; to do this, take care of the heat source and close the wood piece in the steam box. For every 2.5 cm of thickness of the workpiece, the product needs to be steamed for about an hour. At the end of the time, the tree must be removed from the box and given the desired shape. The process should be completed very quickly. The workpiece is bent carefully and softly.

Some types of wood bend more easily than others due to different elasticity. Different methods require different amounts of force to be applied.

When the desired result is achieved, the bent tree must be fixed in this position. It is possible to secure the tree during its formation. That is why it is easier to control the process.

Using chemical impregnation

In order to destroy the lignin bonds between fibers, it is possible to influence the wood with chemicals, and this can be done to the fullest extent at home. Ammonia is ideal for this. The workpiece is soaked in 25% aqueous solution ammonia. At the end of which it becomes very obedient and elastic, which allows you to bend, twist it and squeeze out relief shapes in it under pressure.

Ammonia is scary! Based on this, when working with it, you should follow all safety regulations. The soaking of the workpiece should be carried out in a tightly closed container located in a well-ventilated room.

The longer the wood is in the ammonia solution, the more plastic it becomes. After soaking the workpiece and giving it shape, it is necessary to leave it in this curved form. This is necessary to fix the shape, and so that the ammonia evaporates. Again, bent wood should be left in a ventilated area. It is noteworthy that after the ammonia has evaporated, the wood fibers will regain their former strength, and this will allow the workpiece to retain its shape!

Layering method

First you need to make a piece of wood that will be bent. The boards should be slightly longer than the length of the finished part. This is explained by the fact that bending will shorten the lamellas. Before you start cutting, draw a diagonal line with a pencil. This must be done across the underside of the board. This will allow the lamella sequence to be maintained after they have been moved.

The boards are cut with a straight edge, never with the right side. So, it will be possible to put them together with the slightest transformation. A layer of cork is applied to the mold. This will help avoid unevenness in the shape of the saw, which will allow you to make a clearer bend. In addition, the cork will keep the delamination in shape. Now glue is applied to the top side of one of the wooden slats.

The glue is applied to the lamellas with a roller. It is best to use urea-formaldehyde glue, which consists of 2 parts. It has a high level of adhesion, but takes a long time to dry. In addition, it is possible to use epoxy resin, but such a composition costs a lot, and not everyone can afford it. Regular wood glue cannot be used in this case. It dries quickly, but is very soft, which is not welcome in this environment.

Blank from bent wood be directed as quickly as possible to place in the mold. So, another lamella is placed on top of the lamella coated with glue. The process is repeated until the bent piece reaches the desired thickness. The boards are fastened together. Once the glue has completely dried, proceed to shorten it to the desired length.

I drank it as a way

The prepared piece of wood must be sawn through. The cuts are made 2/3 of the thickness of the workpiece. They should be on the inside of the bend. Be extremely careful, as rough cuts can break the tree.

The key to success when cutting cuts is to keep the distance between cuts as even as possible. Perfectly 1.25 cm.

The cuts are made across the grain of the wood. Then try to squeeze the edges of the workpiece so as to connect the gaps together. This is the shape the bend will take upon completion of the work. After this, the bend is corrected. Much more often outside treated with veneer, in some cases laminate. This effect allows you to correct the bend and hide any flaws made during production. Spaces between bent tree hiding is simple - to do this, glue and sawdust are mixed, and when finished, the gaps are filled with this mixture.

Regardless of the bending method, once the wood is removed from the mold, the bend will easily relax. In view of this, it needs to be made a little more in order to compensate for this effect later. The sawing method can be used when bending part of a box or an iron corner.

So, using these simple tips It is possible to bend a tree with your own hands without much effort.

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 consider theoretical aspects 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 cut surfaces are obtained and, in connection with this, the processing conditions on milling machines and finishing. In addition, cutting produces a large amount of waste. The production of curved parts by bending requires a more complex technological process and equipment compared to sawing. However, when bending, the strength of the parts is completely preserved and even in some cases increases; no end surfaces are 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 magnitude of normal stresses changes along 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 a block of rectangular cross-section is bent along a circular arc and that the deformations in the block are directly proportional to the stresses, and the neutral layer is located in the middle of the block.

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). The total length of the stretched part of the bar 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. bending elongation 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 = )