Curvilinear furniture frame structures are difficult to produce, and large curves cut from straight sections of wood will require complex manufacturing techniques to avoid the weakness of short fiber and large, uneconomic waste. However, using dry or wet bending techniques, complex curved shapes can be produced quite economically, and since the fibers will run along the bend rather than across it, the finished product will be stronger. Dry bending involves first dividing the wood into thin sections, but thicker pieces can be bent by soaking or steaming.
Michael Toneti's bent cafe chairs and rocking chairs are classic examples of bent furniture made using steaming, and in the thirties of the 20th century, furniture made from laminated materials became an element of high fashion, after the invention of industrial production methods different varieties plywood. Both steam bending and layer bending can be accomplished in the home workshop, and both methods continue to be used in the antique furniture industry and by skilled craftsmen and designers.
Steamed wood can bend with a relatively large bending steepness. The steam softens the wood fibers enough to bend them and mold them into the desired shape. It may require significant bending force, but it is quite achievable in a home workshop using basic equipment. You will need to make a template, a clamping clamp and a steam chamber. Wood bending is not a precise procedure. There are many options, and often trial and error is the only way to possible ways obtaining the required result.
Thin wooden blanks don't require preliminary preparation. The minimum radius to which it can be bent will depend on the thickness and natural properties of the wood species. Thin wood, in the absence of deformation limiters (and in the form of, for example, a template), when bent freely, will take the shape of a ring if the ends of the workpiece are brought together. To obtain a greater bend steepness, the wood needs to be steamed and “kept” fixed on the template so that it takes the required form, stabilized in this position due to internal residual deformation. When thick wood is bent, it is necessary to limit the stretching of the outer layers to prevent them from peeling off or breaking. The method described here is intended for bending relatively thick pieces of wood.
Wood preparation
For bending, choose straight-grained wood without knots or cracks. Any defect or flaw is potentially a weak point, so certain failures are possible. There are dozens of types of wood that can be successfully steam-bent, and many of them are hardwoods. In the table below you can find a short list of suitable types of material for bending. You can bend well-dried wood, but freshly cut wood is easier to process. Atmospheric-seasoned wood bends better than chamber- or oven-dried wood. If the wood is too dry and difficult to work with, you can soak it for several hours before steaming.
Depending on the type of workpiece, you can cut it to size in advance or do it with a saw, plow or stapler after bending. The latter method is often used in the production of bent furniture such as Windsor chairs and armchairs. Wood with an even and smooth surface finish is less susceptible to delamination and will make final finishing the entire product is lighter. Raw wood shrinks more than seasoned wood, and when processed lathe before bending, it tends to take on an oval cross-section when drying. Regardless of the shape and size, make the length of the workpiece longer finished product approximately 100 mm. Then, in case of delamination or splitting of the ends after bending, it will be possible to trim off the damaged areas.
To calculate the length, make a drawing of the bend shape on a scale of 1:1. Measure the outside of the curved piece to get correct value its length. This will prevent unnecessary stretching of the external fibers, which could lead to cracking under the influence of internal stresses. The softened inner fibers will be able to shrink enough to take the shape of a smaller inner bend.
The key to making a tight bend is to use a flexible clamp. Make a clamp from mild steel, 2mm thick and at least as wide as the workpiece you bend. This will work for almost any job you might need to do. To avoid possible contamination surface of the part as a result of interaction reactions chemical elements wood, metal and environment, make a clamp from of stainless steel or galvanized steel or use a polyethylene gasket.
Install end stops or stops on the clamp to fix the ends of the workpiece, thereby preventing the fibers from stretching and delaminating outside curved part. These stops must be strong enough to withstand significant pressure on them, and be of sufficient size so that the end of the workpiece can rest against the stop with its entire surface. You can make them from thick metal corner or from hardwood, which is usually easier to do.
To equip the clamp with reliable end stops, install on the ends metal tape wooden blocks approximately 225 mm long. Along the center lines of each block, drill two holes with a diameter of 9 mm at a distance of about 150 mm from each other. Mark and drill the clamp strip for the end stop mounting bolts. The distance between the stops must be equal to the length of the workpiece, including the allowance. To ensure that the clamp has a lever action that is convenient for operation, attach sufficiently strong wooden blocks to the ends of the strip on its back side using long bolts for fastening the stops.
Making a template
Steamed wood is bent into a pattern that defines the shape of the bend and provides support for the fibers of the interior of the curved piece. The template must be very strong and have a width that is at least equal to the width of the part being bent. It must provide certain possibilities for fixing the workpiece on it using clamps or other clamps.
You can make a template from thick wood, setting the mold on a base made of artificial wood materials, or use sheets of plywood glued together. Because the bent wood tends to straighten after releasing the clamp, it is necessary to adjust the shape of the template taking into account the straightening of the part. To do this, you will have to use the most reliable one, although not always in a pleasant way- trial and error to determine the parameters of such correction.
Types of wood for bending with steaming
- Ash
Fraxinus excelsior
Fraxinus amcricana - Beech
Fagus grandifolia
Fagus sylvatica - Birch
Betula pendula
Benda alleghaniensis - Elm
Ulmus americana
Ulmus procera
Ulmus liollandica
Ulmus thomasii - Hickory Cartja spp.
- Oak
Quercus rubra
Quercus petraea - Nut
Juglans nigra
Juglans regia - Yew
Taxus baccara
Making a steam chamber
Make a steam chamber from plywood for outdoor use or use plastic or metal pipe boxes. Plywood allows you to make using glue and screws simple design exactly according to your specific requirements. This type of chamber is ideal if you plan to steam entire batches of wood. Camera made of plastic or metal pipe limits the range of sizes, but is quite suitable for small workpieces.
Cut a piece of pipe to the required length in accordance with the dimensions of the workpiece. Length 1 m - convenient size, which allows you to process entire workpieces or even parts of increased length if it is necessary to bend only its end part. Make removable push-in end flaps from plywood for outdoor use. Drill a hole in one of them for the steam pipe and use a plane to plan the lower part of the edge of the other damper to create ventilation and drainage hole. Make special “open” flaps with a hole for long workpieces. Install corpses inside wooden supports so that the workpiece does not touch the bottom of the chamber. Insulate the chamber using polystyrene foam or wooden blocks, securing them to the chamber with wire. Place the camera on stands with a slight inclination to allow condensation to drain out. Provide a receptacle for any leaking water.
Steam can be produced using a small electric evaporator or a factory-made steam generator, or you can make your own evaporator from metal tank for 20-25 l with a removable lid or stopper. Connect one end of a short rubber hose to a pipe or valve (valve) soldered into the tank, and insert the other into the hole in the chamber damper. To heat water you can use any heating device, such as an electric or gas stove. Fill the tank halfway with water and heat it to 100 °C. to ensure a constant flow of steam. As a guide, wood should be steamed for 1 hour for every 25 mm of thickness. Longer steaming will not necessarily improve the ductility of the wood, but may destroy its internal structure.
Wood bending
You will only have a few minutes to secure the workpiece into the template before it begins to cool and stabilize. Prepare in advance workplace. Have a sufficient number of clamps available and, in the case of processing very thick wood, negotiate with a friend for help.
Turn off the steam supply and turn off the steam generator. Remove the workpiece from the chamber and place it in a pre-sized and heated clamp. Install it all together on the template. Secure the center by placing a piece of wood between the clamp and the clamp. Tightly screw the workpiece onto the template and clamp securely in place with several clamps. Allow the part to stabilize for at least 15 minutes before transferring it to a uniformly shaped drying mandrel or template. You can leave the blank on the first template. In any case, aging of the material should take from 1 to 7 days.
Security measures
When bending with steaming, observe following rules:
- Do not over-tighten the steam generator cap or plug.
- Provide ventilation for the steam chamber.
- Do not operate the steam generator without water.
- Do not stand or lean over the steam generator or steam chamber when opening them.
- Wear thick gloves or mittens when handling heated workpieces and steaming equipment.
- The source of steam must be removed at a considerable distance from flammable objects and materials.
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 drying them 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 a given temperature in the center of the steamed workpiece, 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 workpieces, peeled veneer, urea-formaldehyde resins KF-BZH, KF-Zh, KF-MG, M-70 are used, particle boards P-1 and P-2. 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 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, hardwood and coniferous species, made of 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-laminated 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, a groove is selected in the slab after veneering and sanding in the place where the bend will be. The groove can be rectangular or dovetail type. 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 an angle greater strength into it with inside You can put a wooden square.
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 curved shape.
How to bend a tree?
No, our task is not at all to bend an innocent plant. It's about 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? Hold 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, such species 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. You can clamp the bent plywood between two spacers and press it 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 that we have 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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The first thing you need to do is steam wooden block. There are several ways to do this. Sometimes builders limit themselves to steaming in hot water, but it is best to build a special box into which streams of hot and humid air. This is done very simply. Pour water into any saucepan or kettle and bring to a boil. Then a rubber tube is inserted into any hole in this container, and its other end is inserted into a pre-cut hole in the box. So wet and hot air will go into the box. As a rule, 1 hour of steaming is enough for the full effect. Try not to over-steam your bar, because... This won't lead to anything good either.
Step 2
Now you can begin the bending process itself. To do this, special templates are used, according to which the bend must be carried out, i.e. One part of the block is leaned against a wooden template and, with the help of strong pressure, it receives the same shape. It is important that one side of the bent bar is firmly secured. The likelihood of cracks appearing is extremely low, but it is still better to bend the block carefully, without strong and sudden pressure.
Step 3
After bending, the block must be left alone and allowed to dry. When it dries, it will not change its shape, so you can simply put it on a dry surface and hit sun rays place. After drying, it can be coated with varnish or paint.
*information is posted for informational purposes, to thank us, share the link to the page with your friends. You can send material interesting to our readers. We will be happy to answer all your questions and suggestions, as well as hear criticism and suggestions at [email protected]One of the ways to process carpentry blanks is bending. Wooden blanks treated with hot steam are able to bend and, after drying, retain the resulting shape. Such technological process is not particularly difficult, but some features of how to bend wood should be taken into account. You may also be interested in pine stairs, which you can order on the website http://mirdereva.ru/.
Wood fibers are held together by a special substance - lignin, which, under the influence high temperature softens, and after cooling again binds the fibers. The process of bending blanks is based on this. Please note that wood different breeds bendable in its own way. For bent products, it is best to use oak, beech, birch, yew, cherry, and elm. But pine, spruce, cedar, and alder should not be used for these purposes.
Work on bent parts begins with the choice of material. The workpieces must be straight-grained; the use of wood with curved fibers is not allowed. The prepared material is dried in natural conditions, under canopies, to a humidity level of no more than 20%. But artificially dried wood should not be used for bending, since it is less amenable to such processing. If you have to use such material, then before bending it must be soaked in water (at least a week). Soaking is also necessary for hard wood such as oak, ash, and beech.
To heat the workpieces before bending, it is best to use a steam chamber. It is easy to make such a camera at home using plastic pipe suitable sizes and regular kettle. The parts are placed in a pipe, and steam is supplied from the kettle. The exposure time in the chamber depends on the size of the part and is determined experimentally. In this case, you can be guided by the fact that for 1 cm of the thickness of the workpiece, 30-40 minutes of steaming the wood are required.
In places of bending on parts, if the design of the product allows it, you can slightly reduce the thickness of the material and remove the chamfers. This will make the bending process easier. Thin workpieces, in the absence of a steam chamber, can be heated over an electric or gas stove.
Before you start bending wood, you need to prepare a form on which the part will be fixed, and clamps for fixation. It should be borne in mind that after heating the wood, there will be very little time to fix the workpiece, no more than 5 minutes. Therefore, everything needs to be done quickly, but if the part begins to cool, then it should be heated again. Otherwise, the workpiece may break.
Therefore, it is important to provide a design of molds and clamps that would allow the workpiece to be quickly fixed in the desired position. If the molds are made of wood, they should not be covered with any protective compounds, paint, varnish. Firstly, they deteriorate from heating, and secondly, they will interfere with the drying of the workpieces.
Short workpieces are bent on mandrels larger radius, and then they are fixed in shape. This pre-bending reduces the likelihood that the part will break as the bend is formed. You need to keep the parts in shape until they dry completely so that they do not bend back. This usually takes 6 to 9 days and is determined empirically.
After freeing the workpiece from the clamps, it must be put aside for a day, and only then begin processing and finishing. This is necessary in order to relieve residual extension stresses. The tips are simple, but they will allow you to easily master the process of bending wood.