How to bend hardwood. Tips for the master: how to bend wood. Here is a photo of such a system

When bending wood, there are many things to consider: fresh wood is best suited for this business, it takes a certain amount of time to steam the wood, which depends on its thickness.

Processes for changing the properties of wood to meet requests: technology and properties Wood is a natural polymer composite material, which, under mechanical and chemical action, changes its properties. Knowing the patterns of material change, it is possible to create them purposefully, giving the qualities required by the consumer. This is called the wood modification process. It is necessary in the production of chipboard, MDF, OSB, WPC and other wood-based materials, where chopped wood mixed with a polymer binder is pressed to obtain a homogeneous material of standard sizes.
The proposed wood modification technology changes the properties of wood in the array, that is, to the entire depth of the processed material, without resorting to its grinding. This is achieved by the fact that the molecules of the modifier, i.e., the substance that contributes to changing the properties of wood, are comparable in size to the molecules of the wood substance and less than the size of the intercellular spaces in it. Therefore, by means of diffusion or forced impregnation under pressure, the modifier penetrates the entire thickness of the impregnated product, and then, under the influence of temperature and pressure, reacts with natural chemicals found in the wood substance.

Thus, the technology allows not to grind wood, not to use expensive polymer binders, and to achieve the same effect that was achieved in the production of MDF, for example, but in a cheaper way. At the same time, it is preserved with all its positive properties, the texture stands out brighter, you can change the color (lamination is not required).
So, the modifier in the dissolved state must penetrate into the cellular, be chemically active for the components that make up the wood substance, and, reacting with these components, purposefully change the physical and operational properties material. The most suitable substance for this is urea, because in the previously mentioned MDF or OSB, the most applicable binders are carbamide. Carbamide is soluble in water, including that contained in a bound state in wood, which means that by impregnating wood with an aqueous solution of urea, we, paradoxically, “dry” it, “taking” part of the wood moisture on hydrophilic urea. Carbamide or urea actively reacts with such components of the wood substance as lignin, hemicelluloses, and extractives.
And since the polycondensation reaction occurs in the macromolecules of the wood substance, the wood mass acquires new parameters set by the manufacturer. useful qualities while retaining the positive old ones. The solution of carbamide is not harmful, chemically neutral, moreover - urea grade A according to GOST 6691-77 is used as a feed additive for livestock. Urea-modified wood is certified (GOST 24329-80) and is mainly used under the trademark "Destam" or "Lignoferum" in the production of bearing shells. In the production of building and joinery products, thermally modified wood is also currently used, the technology of which is similar to the proposed one, except that the chemical modification of the wood substance is carried out in the absence of carbamide due to the polycondensation of the decomposition products of lignin, hemicelluloses, extractives and xylans.
Due to thermal degradation, they partially decrease physical and mechanical properties thermomodified wood. Technological process the production of mechanochemically modified wood consists in the impregnation of the original wood of any species and any humidity with a modifier solution. Impregnation can be carried out by the method of "hot-cold baths" - diffusion or in an autoclave - forced. Then drying is carried out, if necessary - with compaction (pressing), and heat treatment, which fixes the new properties of wood. It should be noted that it is more economical to use low-value breeds, since their operational properties after modification are superior to those of expensive breeds.

How to bend wood correctly and in what way?

Manufacturers are currently wooden products they prefer to do without this operation, and if they use bent elements, then from plywood. It's easier to bend plywood. It should be noted, however, that furniture makers natural wood have long ceased to pamper the buyer. All furniture is made of wood or fiberboard. Products made of bent wood, whether it be a chair or something else, are without a doubt stronger, lighter and more elegant.

Choice of wood

The success of bending largely depends on the type of wood chosen. Almost any breed can be bent, but elm, oak, beech, have the best flexibility. If carefully dried wood is needed for carpentry work, then in our case it is better to use freshly harvested wood. Do not take old (by age) wood. How younger tree, the more flexible it is. From the desired breed, you need to choose pieces without cracks, without knots. At the very least, knots should not be in the place of the intended bend. It is important that the wood is straight-grained, without strands, cross-layers and “screws”. It is best to prepare not sawn boards and beams, but solid round timber.

Making a workpiece

Blanks for bending wooden elements are best obtained not by sawing, but by splitting round timber. The direction of the split should be along the chords of the circle in order to exclude a fragile and unsuitable for bending core. prepared in this way wooden blocks and planks will not flake off during bending. The future part is marked so that the direction of the bend coincides with the radius of the round timber from which the workpiece was chipped off, and the outer side of the bend coincides with the outer part of the former round timber. Chipped workpieces are processed with planers to the right sizes with a small allowance for finishing.

Steaming the workpiece

To give the workpiece the best plasticity, it must be steamed. To do this, you need a metal container of a certain size. In it, the blanks will be “steamed” in their entirety or only in the place of the bend. The second is preferable, since it is more convenient to take the workpiece simply with your hands (without devices), which you cannot do if the workpiece is all steamed.

If this species works are supposed to be put on stream, then it is possible to make a special metal container with a sealed lid and two holes for placing the bent part inside the “steam room”. This whole simple structure must be tightly closed in order to reduce the release of steam to the outside. Put under the lid rubber gasket. It is impossible to screw tightly, swelling or even an explosion under steam pressure can occur. A sufficiently heavy lid will ensure tightness and at the same time work safety valve when the pressure is too high.

It is difficult to specify the time for complete steaming. It depends on the type of wood, the section of the blanks, the degree of dryness of the blanks. Just from time to time you need to take out the workpiece and try it for bending. The readiness of the workpiece will be felt immediately by bending compliance.

Workpiece bending

It is best to bend the workpiece in a template. The blank, bent and dried in the template, will provide the part configuration we need. Especially if you need not one, but several completely identical parts.

With a certain skill, you can do the same as a shower for a horse harness is made - the steamed blank is bent and the ends are tied with a rope. In this form, leave until completely dry. It is necessary to dry bent parts in a ventilated place protected from the sun. Attempting to artificially accelerate drying by heating can lead to cracking of the wood.

It should be noted that after removing the part from the template, it “loses” a little, i.e. straightens up. Given this property, the blanks must be bent a little “cooler” so that the desired shape is obtained upon release. How much "cooler" is a matter of experience. Much depends on the section of the workpiece, the type of wood, the degree of its steaming before flexible.

Press for bending wood materials

Manufacturer ORMA, Italy

Purpose
This equipment is designed for bending (bending) wood materials. Before bending, the blanks are steamed in specialized chambers. Stabilization of the workpiece is carried out by high frequency current.
This equipment has found wide application in the manufacture of chairs, sledges, school furniture.

Specifications:

The complete bending kit includes
- Steaming chamber - a reservoir for moistening blanks with a condensate collector, complete with a steam generator (a separate generator for each autoclave)
- Pre-bending press (required depending on tasks and performance)
- Bending and stabilization press (selected depending on the tasks and productivity), depending on the complexity of the product, it can be equipped with additional side cylinders. The possible total force is vibrated from 30 to 120 tons. Specific pressure up to 7.5 kg/cm2
- Electronic generator frequencies - with the ability to work on two presses for bending and stabilization

Norms and structural strength of bent wood

In addition to the traditional use of bent, construction structural elements performed in this way. Usage load-bearing elements from bent wood allows you to create new interesting views architectural solutions, which, combined with optimal economic indicators such structures explains the increased interest in them from the side practical application not only in industrial, but also in private housing construction.

There are two ways to make a curved structure from bent wood: sawing it out of boards, bending timber (solid bent products) or layers of wood with their simultaneous gluing (curved glued products). The process of bending wood is based on its ability to certain conditions under the influence of external loads to change its shape and keep it in the future.

It is clear that to cut a product from the board large sizes and curvature is almost impossible, therefore, in order to make a bent board or beam at home for building a beautiful or a dome crowning a decorative turret at home, you should prepare everything you need for bending wood. Just as website optimization allows you to increase the rating of an Internet resource, so the choice quality material for bending improves its result. Selected as preparation unedged board or timber without knots, with an oblique layer of not more than 10% of the surface area. The best varieties woods with increased plasticity are hornbeam, maple, beech, oak, ash and elm.

After the material is selected, it is possible to start the bending process, the main stages of which are: hydrothermal treatment, blank bending and product drying. Optimal parameters, at which the bending takes place with the highest quality, are the moisture content of the wood in the range of 25-30% and the temperature in the center of the workpiece from 80 to 90 ° C.

Professional promotion of sites dedicated to the intricacies of wood bending technology will surely arouse the interest of a wide audience, since the simplicity of this process is incomparable with the result obtained. Hydrothermal consists in steaming or boiling the workpiece in hot water.

Steaming is technically more difficult, so at home it is easier to organize the boiling of wood in the cooking tank right size. The workpiece removed from the brewing tank should immediately be secured to the rail with clamps while the wood is warm. Otherwise, stresses will arise in its outer layers, leading to cracks.

Flexible plywood and its application

Flexible plywood (plywood for bending) is now in great demand, due to the fact that it is comfortable material for the manufacture of structures in which rounding is necessary. The use of such bending plywood is effective and expedient, since it takes any necessary shape. Its flexibility allows you to embody the wildest fantasies of designers and produce the most fashionable and modern furniture, be it a closet with original design for your living room, cute shelves for the kitchen or modern and comfortable office furniture.
Such plywood is made from tropical trees, mainly from CEIBA wood, but sometimes flexible plywood is also made from other woods: Parika, Keruing. Flexible (bending) plywood is, as a rule, a 3-layer board, which is glued together in the transverse or longitudinal versions of the jackets.

Flexible plywood, can be used for all types of bends, even very small radii. It does not need to be heated and treated with water. The self-supporting construction of the bending plywood makes the use of structural and special supports unnecessary. Unique designer models, rounded designs and complex shapes with several radii, which cannot be created from traditional materials, are made easily and quickly. Flexible plywood fulfills almost all thickness requirements by increasing the number of layers of material (for example, increasing the thickness to 10mm, 15mm, 16mm, 18mm, 20mm, etc.). Large thickness sheets can be obtained by gluing several sheets of thinner bending plywood together.

Tropical high quality plywood is a combination modern technologies and traditional materials. A product designed to satisfy the most sophisticated needs modern manufacturers furniture and joinery. Flexible plywood (bending plywood) is cheaper than pre-made wood molds. Significant time savings, less labor intensity and greater profitability - these are its advantages over any other way to change the shape of plywood.

In addition to flexible plywood, our company offers another unique product - Ultralight plywood. The range of use of this plywood is also quite wide: it is the production of door panels, the production of cabinet furniture, sofas, armchairs, shelves. Ultralight plywood is a new product on our market, it is 1.8 times lighter than birch. This plywood is well veneered with veneer, finished with films and varnishes, and most importantly, it allows you to significantly reduce the weight of the finished product!

Specifications

Direction of bend Across the grain: along the width

Composition Hot pressed tropical wood with thermal setting adhesive

Density 300-400 kg/cu.m.

Thickness 5mm, 8mm, etc.

Dimensions 2500/2440 mm x 1220 mm etc. order

Bending radius For 5 mm thick, min. 7 cm for 8 mm thick min. 10 cm

Elasticity
Perpendicular to fibers: 210 N/mm2
Parallel to fibers: 6300 N/mm2
(For 5mm panel at 10% humidity)

Store panels in horizontal position in a clean, shady, dry place.

Apply glue to the panels, fixing the desired shape. After the glue dries, the panel will retain its shape. H.P.L. or the plywood can be glued either during the initial molding or in a separate, final step.

You can use any wood glue.

Panels must be transported on a hard, flat surface. Individual panels can be rolled up, but they should not be stored in this position for long periods of time.

Bending is widely used in industries such as shipbuilding. To begin with, there are a few basic rules that are always respected.

By steaming the wood to bend it, you soften the hemicellulose. Cellulose, on the other hand, is a polymer that behaves like resins - thermoplastics. (Thanks to John McKenzie for the last two suggestions).

To do this, you need heat and steam at the same time. In Asia, people bend wood and just over a fire, but that wood is definitely quite wet - usually freshly cut. Shipbuilders in ancient Scandinavia harvested materials for plating their ships and put them in a salt water swamp to keep them flexible until they needed to be put to work. However, we are not always able to get freshly harvested wood and excellent results can also be achieved using ordinary 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 is about steaming time: one hour for every inch of wood thickness.

Be aware that along with the probability of understeaming the workpiece, there is also the possibility of oversteaming it. If you have steamed an inch board for an hour and it cracked when you tried to bend it, you should not conclude that there was not enough time. There are other influencing factors that explain this, but we will return to them later. Longer steaming of the same workpiece will not give positive result. It is not bad in such a situation to have a workpiece of the same thickness as that intended for bending and which is not a pity. Preferably from the same board. Steam them together and after presumably required time get a test sample and try to bend it into shape. If it crackles, then let the main workpiece steam for another ten minutes. But no more.

Wood:

Usually, the best option it will if you can find freshly cut wood. I understand that the carpenters-carpenters will shudder at these words. But the fact remains that fresh wood bends better than dry wood. You can take a two-meter-inch board of white oak, clamp one end of it in a workbench and bend it to any desired curvature - fresh wood is so malleable. However, of course, she will not remain in this state and she will still have to soar.

In shipbuilding, the main evil is rot. If you are concerned about this issue, then take note that the mere fact of steaming fresh wood eliminates its tendency to rot. Therefore, you don’t have to worry - the frames of the boats are usually made from fresh oak bent under steam and do not rot if cared for. It also means that at least blanks for the Windsor chair can be made in this way. But air-dried oak also gives an excellent result.

When selecting wood for bending, one thing should be avoided - the oblique layer. If you try to bend such a workpiece may burst.

Therefore, regarding the moisture content of wood, the rules are as follows:
1.Fresh wood is best.
2. Air-drying wood is the second good option.
3. - the third and very far from the first two options.

If all you have is after the dryer and nothing else to get - well, then you have no choice. But still, if you can get air-dried wood, it will be much better.

Instruction

For the manufacture of curved wood parts, two main methods are used: sawing according to a template and bending pre-steamed wood using a template on special machine. The first method leads to cutting the fibers and reducing the strength of the parts. Bending provides a high percentage useful output parts and great strength. Bent parts can be finished with high quality and subject to various machining(profiling, forming spikes, eyes, etc.).

Ability wooden board to bending is determined by the plasticity of wood and depends on the type of wood. Beech, birch, oak, pine and spruce have the highest plasticity. But it is possible to control the plastic properties of the workpiece by carrying out its hydro heat treatment.

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

The processing of the workpiece consists in boiling it in hot water or steaming saturated steam low pressure. Steaming is more common, because during this treatment the wood warms up more evenly, there is no excessive moisture in the wood.

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

The outer layer under the action of tensile stresses will receive elongation, and the inner one will become shorter. The amount of deformation depends on the thickness of the dock and the radius of the bend. To limit the elongation of the wood fibers and prevent their possible rupture, a special tire made of steel up to 2.5 mm thick is placed on 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 the bending occurs only due to compression.

When making a wide variety of joinery, the craftsman often has to use curved parts. It is not always possible to obtain the required shape by sawing, since it is important here to ensure the strength of the material and its economy. 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.

Instruction

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

Carefully select which you will subsequently bend. Use boards sawn lengthwise for this processing. Avoid defective and kinky boards, as well as those blanks that have knots. If materials with damaged fibers are used, the workpiece may crack at the location of the defect.

If there is a need to make a curved wooden element, then at first glance it may seem that it is easier to cut desired element in a curved form, but in this case the fibers wood material will be cut, thus weakening the strength of the part, and as a result, the entire product. In addition, when sawing out, a large waste of material is obtained, which cannot be said about the method when a wooden blank is simply bent.
Wood is cellulose fibers bound together by a chemical called lignin. The flexibility of the tree depends on the arrangement of the fibers.
Note! Only well-dried wood will be a reliable and durable source material for the production of various products. However, the change in the shape of dry wooden blank process is complex, because dry wood may break, which is very undesirable.

Having studied the technology, how to bend a tree, as well as the basic physical properties wood, which allow you to change its shape and subsequently save it, it is quite possible to do wood bending at home.
Some features of working with wood
The bending of wood is accompanied by its deformation, as well as compression of the inner layers and stretching of the outer ones. It happens that tensile forces lead to rupture of the outer fibers. This can be prevented by preliminary hydrothermal treatment.
So, you can bend the blanks of a bar made of solid wood and glued wood. In addition, planed and peeled veneer is used for bending. Hardwoods are the most plastic. Among them are beech, ash, birch, hornbeam, maple, oak, poplar, linden and alder. Bent glued blanks are best made from birch veneer. It should be noted that birch veneer occupies approximately 60% of the total volume of bent-glued blanks.
When steaming the workpiece, the compressibility increases significantly, namely by a third, while the tensile ability increases by only a few percent. And, therefore, it is not worth a priori to think about whether it is possible to bend a tree thicker than 2 cm.

Heating in a steam box

First you need to prepare a steam box. It can be handmade. Its main task is to hold the tree that needs to be bent. It must have a hole designed to release steam pressure. Otherwise, it will explode.
The steam outlet should be at the bottom of the box. In addition, a removable lid should be provided in the box through which the bent tree can be pulled out after it has acquired the desired shape. Clamps should be used to hold the bent piece of wood in the desired shape. They can be made independently from wood or bought in a specialized store.

Round trimmings should be made from wood - a few pieces. Holes are drilled in them off-center. After that, you need to push the bolts through them, and then drill another hole through the sides to push them in tightly. Such simple crafts can become excellent clips.
Now it's time to steam the wood, for this you should take care of the heat source and close the wood blank in the steam box. For every 2.5 cm of the thickness of the workpiece, it takes about an hour to steam the product. After the time has passed, the tree must be removed from the box and given the necessary shape. The process must be very fast. The workpiece is bent neatly and gently.
Note! Some types of wood bend more easily than others due to different elasticity. different ways require the application of a different amount of force.
Once the desired result is achieved, the bent tree must be fixed in that position. You can pin the tree as it is being formed. This makes it easier to control the process.

With chemical impregnation

To destroy the bonds of lignin between the fibers, you can act on the tree chemicals, and it is quite possible to implement this at home. Ammonia is ideal for this. The workpiece is soaked in a 25% aqueous solution of ammonia. After that, it becomes very obedient and elastic, which allows you to bend, twist it and squeeze relief forms into it under pressure.
Note! Ammonia is dangerous! Therefore, when working with it, all safety regulations must be observed. Soaking the workpiece should be carried out in a tightly closed container located in a room that is well ventilated.
aqueous ammonia solution aqueous ammonia solution
The longer the wood is in the ammonia solution, the more plastic it becomes. After soaking the workpiece and shaping it, you need to leave it in such a curved form. This is necessary to fix the shape, and, well, in order for the ammonia to evaporate. Again, bent wood should be left in a ventilated area. Interestingly, after the evaporation of ammonia, the wood fibers will regain their former strength, and this will allow the workpiece to hold its shape!

First you need to make a blank of wood, which will be bent. The boards should be slightly longer than the length of the finished piece. This is because the bend will shorten the lamellae. Before you start cutting, you should draw a diagonal line with a pencil. You need to do this across the bottom side of the board. This will keep the sequence of slats after they are moved.
The boards are cut with a straight edge, in no case front side. So, they can be added together with the least change. A cork layer is applied to the mold. This will help avoid irregularities in the shape of the saw, which will allow you to make a sharper bend. In addition, the cork will hold the delamination in shape. Now glue is applied to the top side of one of the wooden lamellas.
Glue is applied to the lamellas with a roller. It is best to use a 2-part urea-formaldehyde adhesive. He possesses high level adhesion, but takes a long time to dry. You can also use epoxy resin, but such a composition is very expensive, and not everyone can afford it. Standard wood glue cannot be used in this case. It dries quickly, but is very soft, which in this situation is not welcome at all.
Boards are bonded after gluing Boards are bonded after gluing
The bent wood blank should be placed in the mold as soon as possible. So, another one is laid on a lamella smeared with glue. The process is repeated until the bent blank acquires the desired thickness. The boards are fastened together. After the glue is completely dry, shorten it to the desired length.

Drank like a method
The prepared wooden piece must be sawn through. Cuts are made at 2/3 of the thickness of the workpiece. They must be with inside bending. You should be extremely careful, because rough cuts can break the tree.
Note! The key to success when cutting kerfs is to keep the distance between the kerfs as even as possible. Ideally 1.25 cm.
Defects can be hidden with veneer Defects can be hidden with veneer
The cuts are made across the pattern of the wood. Next, you should squeeze the edges of the workpiece so as to connect the resulting gaps together. This shape will acquire a bend at the end of the work. Then the bend is corrected. More often outside processed with veneer, in some cases with laminate. This action allows you to correct the bend and hide any defects made during the production process. The gaps between the bent tree are hidden in an elementary way - glue and sawdust are mixed for this, and after this mixture the gaps are filled.
Cuts are made across the wood pattern Cuts are made across the wood pattern
Regardless of the bending method, after the tree is taken out of the mold, the bend will relax slightly. In view of this, it needs to be done a little more in order to subsequently compensate for this effect. The sawing method can be used when bending a part of a box or a metal corner.
So, using these simple recommendations you can bend a tree with your own hands without much effort.

Bending wood with steam. Or how to bend a 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 them in action. different systems steam generation. What you are reading now is based on reading literature and personal practical experience. Even mostly experience. I usually worked with oak and mahogany (mahogany). Had a little deal with thin birch veneer. I have not tried other breeds, because I am engaged in the construction and repair of boats. Therefore, I cannot judge with authority about working with other species such as cedar, pine, poplar, etc. And since I didn’t do it myself, I can’t judge it. I write here only about what I personally experienced, and not just 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 respected.

To do this, you need heat and steam at the same time. I know that in Asia people bend wood and just over the fire, but that wood is definitely quite wet - usually freshly cut. Shipbuilders in ancient Scandinavia harvested materials for plating their ships and put them in a salt water swamp to keep them flexible until they needed to be put to work. However, we are not always able to obtain freshly harvested wood for this purpose, and excellent results can be achieved using ordinary 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 is about steaming time: one hour for every inch of wood thickness.

As I found out, along with the probability of understeaming the workpiece, there is also the probability of oversteaming it. If you have steamed an inch board for an hour and it cracked when you tried to bend it, you should not conclude that there was not enough time. There are other influencing factors that explain this, but we will return to them later. Longer steaming of the same workpiece will not give a positive result. It is not bad in such a situation to have a workpiece of the same thickness as that intended for bending and which is not a pity. Preferably from the same board. It is necessary to steam them together and after the supposedly necessary time to get a test sample and try to bend it into shape. If it crackles, then let the main workpiece steam for another ten minutes. But no more.

Wood:

As a rule, the best option will be if you can find freshly cut wood. I understand that the carpenters-carpenters will shudder at these words. But the fact remains that fresh wood bends better than dry wood. I can take a two meter inch board of white oak, clamp one end of it in a workbench and bend it to any curvature I need - fresh wood is so malleable. However, of course, she will not remain in this state and she will still have to soar.

When selecting wood for bending, one thing should be avoided - the oblique layer. If you try to bend such a workpiece may burst.

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

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

If all you have is after the dryer and nothing else to get - well, then you have no choice. I dealt with this as well. But still, if you can get air-dried wood, it will be much better. Just this week I was bending 20mm thick walnut planks for the transom of my yacht. The blanks were dried for several years and their bending went absolutely smoothly.

Steam chambers.

It is absolutely useless, and even harmful for the bending result, to strive to make an absolutely sealed chamber. The steam must leave her. 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 had been steaming it for only five minutes. This is familiar to me after all my experiences.

Cameras can be the most different forms and sizes. It should be large enough so that the workpiece is, as it were, in a suspended state and steam flows around it on all sides. A good result will come from pine boards about 50 x 200. One way to provide "suspension" of the workpiece is to drill through holes in the side walls of the chamber and drive in round hardwood rods of hardwood. With their help, the workpiece will not touch the bottom and the area of \u200b\u200bclosed wood will be minimal. However, you should not make a chamber of such a size 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 (well, or vice versa).

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

I recently found a $50 160,000 BTU propane torch in West Marine's catalog and purchased that as well. With its help, I can bend the frames even for the "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 tank for this purpose. It is possible to put blanks into the chamber only when the installation has reached full capacity and the chamber is completely filled with steam. It must be absolutely guaranteed that the water does not run out prematurely. If this happens and you have to add water, it is better to quit this business. Adding cold water will slow down the generation of steam.

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

Here is a photo of such a system:

In the picture you see a wooden chamber, slightly tilted. Directly below it is the boiler of the steam generator. They are connected to each other by means of a hose from the radiator. If you look closely, you can see an L-shaped pipe coming out at the base of the boiler on the left. This is hard to see in the photo, but its vertical part is actually translucent and thus we will know about the water level inside the boiler. To the left of the cauldron is a white bucket containing make-up water. Look closely and notice the brown tube connecting the bucket to the vertical part of the pipe - the level gauge. Since the bucket is on a rise, the siphon effect is observed: with a drop in the water level in the main boiler, water enters it from the bucket. It can be topped up from time to time, but do it very 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 you can move the workpieces if necessary and remove them if necessary. For example, if you're in the business of making bent frames and you'd like to do it in as little as a day, you fire up the boiler and (when you're at full capacity) put the first blank inside. After 15 minutes, put the second. After another 15 - the third and so on. When it's time for the first one, you take it out and bend it. I assume this procedure will take less than 15 minutes. When she sits still, the second one is already on the way ... and so on. This allows you to do a great job and avoid oversteaming.

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 come out from the end (since steam flow is needed). It must not be allowed that excess pressure will be created in the chamber, making it difficult for steam to enter inside. And besides, the picture itself wooden box, from which steam pours out in clubs, looks quite cool - passers-by just get stupefied. 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 being cooked (with 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 is quick and smooth. The most important thing here is time. You have a matter of seconds for this. As soon as the wood is ready, quickly take it out and immediately bend it. How fast does human dexterity allow. If pressing against the template takes time, simply bend with your hands (if possible). For the frames of my yacht (which have a double curvature), I took the blanks out of the chamber, put one end into the clamp and bent this end and then the second one simply with my hands. Try to provide more fold than is necessary for the template, but not by much. And then attach it to the template.

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

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

It is practically impossible to make blanks of the exact length and expect that it will be possible to provide a bend at the ends. You just don't have the power to do it. For this reason, if you need a workpiece a meter long, and its thickness is more than 6 mm, you'd better cut off a piece of two meters and bend it. I'm just starting from the assumption that you're not in the workshop. hydraulic press- I don't have one myself. When cutting a blank with a margin, remember that the shorter it is, the more difficult it will be to bend.
And if it is with a margin, then the end of the real part will have a large curvature - for an inch oak board, 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 places and take into account the required thickness when choosing a material.

Templates.

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

How much bigger?

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

Warning. If you are bending blanks for lamination, the template should be exactly the shape of the blank in the laminate - I have rarely had a lot of flex in well bent laminated wood.

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

Well, that's probably all my thoughts at the moment.

If it becomes necessary to manufacture a curved wooden element, then at first glance it may seem that it is easier to cut the desired element in a curved form, but in this case 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 out, a large waste of material is obtained, which cannot be said about the method when a wooden blank is simply bent.

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

Only well-dried wood will be a reliable and durable source material for the production of various products. However, changing the shape of a dry wooden blank is a complex process, because a dry tree can break, which is very undesirable.

Having studied the technology of how to bend a tree, as well as the basic physical properties of wood that allow you to change its shape and subsequently save it, it is quite possible to do wood bending at home.

Some features of working with wood

The bending of wood is accompanied by its deformation, as well as compression of the inner layers and stretching of the outer ones. It happens that tensile forces lead to rupture of the outer fibers. This can be prevented by preliminary hydrothermal treatment.

So, you can bend the blanks of a bar made of solid wood and glued wood. In addition, planed and peeled veneer is used for bending. Hardwoods are the most plastic. Among them are beech, ash, birch, hornbeam, maple, oak, poplar, linden and alder. Bent glued blanks are best made from birch veneer. It should be noted that birch veneer occupies approximately 60% of the total volume of bent-glued blanks.

When steaming the workpiece, the compressibility increases significantly, namely by a third, while the tensile ability increases by only a few percent. And, therefore, it is not worth a priori to think about whether it is possible to bend a tree thicker than 2 cm.

Heating in a steam box

First you need to prepare a steam box. It can be handmade. Its main task is to hold the tree that needs to be bent. It must have a hole designed to release steam pressure. Otherwise, it will explode.

The steam outlet should be at the bottom of the box. In addition, a removable lid should be provided in the box through which the bent tree can be pulled out after it has acquired the desired shape. Clamps should be used to hold the bent piece of wood in the desired shape. They can be made independently from wood or bought in a specialized store.

Now it's time to steam the wood, for this you should take care of the heat source and close the wood blank in the steam box. For every 2.5 cm of the thickness of the workpiece, it takes about an hour to steam the product. After the time has passed, the tree must be removed from the box and given the necessary shape. The process must be very fast. The workpiece is bent neatly and gently.

Some types of wood bend more easily than others due to different elasticity. Different methods require the application of a force of different magnitudes.

Once the desired result is achieved, the bent tree must be fixed in that position. You can pin the tree as it is being formed. This makes it easier to control the process.

With chemical impregnation

To destroy the bonds of lignin between the fibers, you can act on the tree with chemicals, and this is quite realistic to do at home. Ammonia is ideal for this. The workpiece is soaked in a 25% aqueous solution of ammonia. After that, it becomes very obedient and elastic, which allows you to bend, twist it and squeeze relief forms into it under pressure.

Ammonia is dangerous! Therefore, when working with it, all safety regulations must be observed. Soaking the workpiece should be carried out in a tightly closed container located in a room that is well ventilated.

The longer the wood is in the ammonia solution, the more plastic it becomes. After soaking the workpiece and shaping it, you need to leave it in such a curved form. This is necessary to fix the shape, and, well, in order for the ammonia to evaporate. Again, bent wood should be left in a ventilated area. Interestingly, after the evaporation of ammonia, the wood fibers will regain their former strength, and this will allow the workpiece to hold its shape!

Lamination method

The boards are cut with a straight edge, in no case the front side. So, they can be added together with the least change. A cork layer is applied to the mold. This will help avoid irregularities in the shape of the saw, which will allow you to make a sharper bend. In addition, the cork will hold the delamination in shape. Now glue is applied to the top side of one of the wooden lamellas.

Glue is applied to the lamellas with a roller. It is best to use a 2-part urea-formaldehyde adhesive. It has a high level of adhesion, but takes a long time to dry. You can also use epoxy resin, but such a composition is very expensive, and not everyone can afford it. Standard wood glue cannot be used in this case. It dries quickly, but is very soft, which in this situation is not welcome at all.

The bent wood blank should be placed in the mold as soon as possible. So, another one is laid on a lamella smeared with glue. The process is repeated until the bent blank acquires the desired thickness. The boards are fastened together. After the glue is completely dry, shorten it to the desired length.

Drank like a method

The prepared wooden piece must be sawn through. Cuts are made at 2/3 of the thickness of the workpiece. They should be on the inside of the bend. You should be extremely careful, because rough cuts can break the tree.

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

The cuts are made across the pattern of the wood. Next, you should squeeze the edges of the workpiece so as to connect the resulting gaps together. This shape will acquire a bend at the end of the work. Then the bend is corrected. Most often, the outer side is treated with veneer, in some cases with laminate. This action allows you to correct the bend and hide any defects made during the production process. The gaps between the bent tree are hidden in an elementary way - glue and sawdust are mixed for this, and after this mixture the gaps are filled.

Regardless of the bending method, after the tree is taken out of the mold, the bend will relax slightly. In view of this, it needs to be done a little more in order to subsequently compensate for this effect. The sawing method can be used when bending a part of a box or a metal corner.

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