Wood bending. Wood bending technologies How to bend hardwood
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 estimated at five points, which greatly expands the scope of use of wooden products. From wood, you can get a wide variety of shapes and sizes of blanks. Special ones help with this. These technologies also include bending and gluing of wood, which are widely used in the modern production cycle.
The entire woodworking process takes a significant amount of time. Wood first - all this happens in woodworking enterprises. In the future, boards and other materials are harvested from wood.
These blanks are sent to factories, where they are already used to make specially 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 manufacture parts of the desired size and shape. Wood splicing can be carried out in width, length or thickness. Pre-prepared ends of the workpieces can have special grooves or spikes, which increases the strength of the parts to be joined. In the gluing process, different types of wood glue are used.
Wood bending is necessary for the production of curved parts. You can bend wood manually, subject to certain features of this work, or on special machines.
The strength and practicality of wooden products, for the manufacture of which special machines for gluing or bending are used, can be estimated at five points. In woodworking industries, they always try to comply with the entire technology of working with wood, and therefore the goods produced are of high quality.
Photo of the methods of wood processing described above
Splicing Bonding Bending
The main stages of gluing technology
Gluing is the main process of working with wood in any furniture production. In order to obtain a solid and high-quality workpiece, it is necessary to strictly observe 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 wood products consists of several stages:
- Preparation of the blanks themselves.
- Selection and application of adhesive composition.
- Actually gluing.
Preliminary preparation of wooden bars and other blanks consists in creating special spikes or grooves in them, which can be done using a special tool - a milling cutter.
Using a wood splicer
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 way of processing wood.
To this woodworking machine, you can pick up cutters of various shapes - sharpened elements with different types of blades. With the help of these cutters, various parts are made.
In the gluing process, milling machines are needed to:
- Cutting spikes of various shapes, with the help of which individual blanks will be glued in the future.
- Creating holes in the material. Devices for folds and grooves, which are also necessary in the process of manufacturing parts of various shapes.
Milling machines are used everywhere, they can be both manual and electric. The ease of manufacturing wooden blanks for gluing using a machine can be rated at four points. In order to get an accurate workpiece, you first need to gain some experience.
This video provides an overview of cutters for wood splicing and making process connections. Shown are cutters for straight and corner splicing, as well as a micro-tenon, 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 dispose of production waste.
Automatic splicing lines include several sequentially operating machines that allow you to end up with the material of the required length and width from short workpieces. With the help of a splicing line, glued beams, which are popular today, are obtained.
The entire technological process when using the production line for splicing wooden blanks consists of several stages, which are provided by the complex of machines included in the installation:
- The cut-off press provides the desired dimensions of the material.
- The milling machine prepares spikes and grooves in wooden blanks.
- The glue applicator distributes the glue according to the set parameters.
- The cross-cutting machine completes the gluing process.
The use of a splicing line in furniture factories ensures high productivity, reduces the number of jobs. , obtained using automatic machines, can be evaluated at five points, since the whole process is strictly controlled.
This is how the automatic length splicing line works:
Types of glue
The correct selection of the type of glue predetermines the quality of the connection of wooden blanks. The choice of glue also depends on the type of wood being glued and on the shape of the blanks. The most commonly used waterproof adhesive compositions.
Several types of synthetic adhesives are used in the furniture industry:
- Thermosetting adhesives are used for gluing spiked 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 to bond wood to other materials - metal, plastic.
- At enterprises engaged in woodworking, glue based on urea resins is most often used. Powdered adhesives are also often used, which require preliminary preparation.
Bonding of parts is carried out in a cold way and by heating them. For gluing blanks along the ribs, an adhesive film is often used, it is sheets of various sizes.
Before gluing the parts, you must first prepare, that is, degrease, remove dirt and various types of stains. After applying glue over the entire surface and connecting the necessary workpieces, the parts are clamped using special devices that are removed only after complete drying.
Machine tools
For splicing glued wood, special machines in the form of presses can be used. In them, the parts are clamped for the required time. This ensures a strong connection between the adhesive surfaces and eliminates the displacement of parts. The press can be selected according to the length of the beam, power, the presence of additional functions.
Gluing wood at home
Gluing wood may sometimes be required at home. Often this happens when sticking wooden furniture sets or during various breakdowns. Before gluing the surface of wooden products must be properly prepared.
To do this, their pores are cleaned from old glue, a layer of paint, 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 supplied with each type of adhesive.
You can clearly see how wood is glued on the video:
bending technology
Wood bending can be defined as the process of bending laminated or solid pieces of wood to give them the desired curved shape. Bending technology is based on the plastic qualities of different types of 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
Hard wood, such as oak, beech, ash, has greater plasticity. Therefore, for the manufacture of curvilinear parts, mainly the species of these trees are used. Distinguish between 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 mode of heating is achieved by boiling in water or by steaming.
The wooden blanks plasticized in this way are bent according to the prepared template and fixed 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 blanks are bent using special machines.
Cold bending is used to obtain multilayer curved bent parts. To obtain a part of the desired shape, you need to lay several workpieces lubricated with glue on top of each other, give them the necessary shape and, using a press machine, withstand the required time. The shape of blanks obtained by cold bending is retained longer.
How to make curved wood, the video will tell:
Bending wood at home
Bending wood at home begins with the choice of material. The prepared parts must be straight-layered, they must first be dried in natural conditions. You also need to soak the parts if they are made of ash, oak, beech. Before bending, the workpiece must be steamed.
To do this, you can use a self-prepared steam chamber. For the manufacture of 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 empirically, but it is believed that in order to achieve the desired plasticity, it is necessary that one centimeter of wood in thickness be steamed for 30 to 40 minutes. It is also not worth overdoing the product.
Before starting bending, you need to prepare the form and clamps. After warming up the wood, it is well exposed to bending for only 5-10 minutes, so you need to do everything extremely quickly. Keep products in shape until they are completely dry, usually it takes at least one week. Then you can process the finished part or spend it.
They use this wood processing process to make different types of furniture with their own hands. At the same time, the price of products is significantly reduced and this can be estimated at five points. But the laboriousness of the whole process takes a lot of time and therefore only truly enthusiastic people can engage in bending wooden blanks and their subsequent use.
Examples of interior elements made of bent wood
Headboard Rocking chair Table Decorative element Chairs
In the woodworking industry, curved parts are produced in large quantities. The production of curved parts is carried out in two ways: sawing from boards or slabs And bending straight bars (solid-bent parts) or layers of wood with simultaneous gluing (curved parts).
Technological process of wood bending. The technological process of bending solid wood bars includes the following operations: preparation of material for bending, hydrothermal treatment, bending and drying.
Preparation of material for bending. Blanks for bending are obtained from unedged boards by cutting them on circular saws. The following requirements are imposed on blanks for bending.
The slant should not exceed 10°. With conventional bending methods, knots are not allowed at all in blanks. In workpieces with simultaneous pressing, knots are allowed to a large extent, which dramatically increases the yield of workpieces. Workpieces should be cut out taking into account allowances for subsequent processing of parts. When bending with simultaneous pressing, in addition to the processing allowance, an allowance for pressing the wood across the fibers and an increased allowance along the length of the workpiece should be provided. In order to increase the yield of blanks for bending, it is recommended to cut the boards after preliminary marking.
At small enterprises, the method of obtaining blanks for bending by splitting blocks has been preserved. The chipped workpiece does not have an oblique layer, therefore, when bent, it gives a lower percentage of rejects. However, this method is very time consuming, since it is performed manually and gives a 20-25% lower yield of blanks from the ridge than when sawing it.
After cutting (or splitting), blanks for round sections are processed on lathe-copying or circular stick machines, and blanks for rectangular sections are processed on longitudinal milling machines. You can also bend unplaned blanks, but in this case the boards are cut with planing saws, which give a clean and accurate cut.
hydrothermal treatment. Hydrothermal treatment of wood before bending is carried out in order to increase the plasticity of wood. Optimum plasticity of wood is achieved when it is heated in a wet state. This is due to the fact that when heated, some of the substances that make up the cells pass into a colloidal state.
As a result, the ability of cells and all wood to deform increases. When drying deformed (bent) wood, colloidal substances harden and retain the shape given to the workpiece.
Hydrothermal treatment of wood before bending is carried out by boiling in hot water or steaming. For boiling, wooden vats or metal baths and tanks are used. Water in bathtubs and vats is heated by steam.
The water temperature is maintained at 90-95°C without bringing it to a boil. The duration of boiling depends on the initial humidity, size and type of wood.
When boiling, it is difficult to obtain a uniform temperature and humidity of the entire workpiece, the outer layers are supersaturated with water. Therefore, boiling in hot water is used only in cases where steaming is technically difficult.
The most widely used in production is the steaming of wood in an atmosphere of saturated steam. Steaming allows you to heat the wood to the desired temperature (70-80 ° C), regulate the moisture content of the wood and get it always close to optimal for bending, i.e. about 25-30%.
For steaming, low-pressure saturated steam (0.02-0.05 MPa) is used, which corresponds to a temperature of 102-105°C. Steaming of wood is carried out in hermetically sealed metal boilers-drums or concrete chambers. The capacity of boilers and chambers is small, designed for laying bars in the amount of 30-40 pieces.
The boilers are located at each bending machine and are connected by a steam pipeline to form a battery. Bars in boilers and chambers are placed on gaskets in order to ensure their best washing with steam.
The duration of steaming depends on the initial moisture and temperature of the wood, the size of the bars and the steam pressure in the boiler. The steaming time is determined by a special diagram. For example, for workpieces with a thickness of 40 mm at an initial moisture content of 30% and a steam pressure in the steaming boiler of 0.03-0.05 MPa, the duration of steaming is 12-13 minutes, and for workpieces with a thickness of 80 mm - 65 minutes.
Plywood in the case of bending to small radii of curvature can also be subjected to hydrothermal treatment. Plywood glued with synthetic adhesives is boiled, and glued with casein or albumin glue is only steamed.
The workpieces removed from the steamer or digester must be bent immediately. It is impossible to allow cooling of the outer layers of wood, which experience the greatest stress during bending.
Wood bending and equipment. Wood bending machines are divided into two types: with cold And hot forms.
Machines of the first type (Fig. 4.13) are used for bending into a closed loop. The bars are bent around a removable, unheated rotating template 6. Template with tire 2 put on a vertical shaft 8 , which is driven by an electric motor through a gearbox 7.
The free end of the tire is fixed in the carriage 4, sliding along guides 3. Bar 5 is laid between the template 6 and bus 2 and is fixed with a movable stop. Then the electric motor is turned on, while the shaft turns 8 with a template put on it and the bar is bent along with the tire.
A roller / is installed at the place of the bend, tightly pressing the bar to the template. The rear end of the tire is fixed with a bracket on the template. The template with the bar and the tire is removed from the machine and sent to the dryer, and a new template is put on the machine, and the operation is repeated.
Rice. 4.13.
7 - pressure roller; 2 - tire; 3 - guide; 4 - bar; 5 - blank;
b - template; 7 - reducer; 8 - shaft
Rice. 4.14.
7 - hook; 2 - template; 3 - emphasis; 4 - tire; 5 - blank
Bending machines with hot molds are called bending-drying machines, they can be with two- and one-sided heating. Machines with double-sided heating are a hydraulic or pneumatic press with heated profiled template plates, between which bending bars are clamped. In these machines, the bars are kept in a clamped state until the mold is completely fixed and the blanks are dried.
In machines with one-sided heating (Fig. 4.14), workpieces 5 are placed between the hot template 2, heated steam, and tire 4 and fastened with an emphasis 3. Curved blanks 5 together with the tires are fixed on the template with special hooks /. The blanks remain in the machine until the shape given to them is fixed.
This is achieved by drying the wood to approximately 15% moisture, which takes 90-180 minutes. To increase the productivity of bending-drying machines, it is recommended to dry the workpieces before bending to 20% moisture, keep them in the machine to a moisture content of 12-15%, and make the final drying to the production moisture content of the workpieces removed from the machine in drying chambers.
Bending of plywood is carried out in templates consisting of two parts: a matrix and a punch, between which the plywood is laid and bent. In this case, special devices, screws, pneumatic and hydraulic presses are used.
Bending with simultaneous pressing consists in the fact that the wood is bent around a template equipped with a notch, and in the process of bending from the outside of the workpiece, it is pressed against the template through the tire by a pressing roller.
The workpiece is being rolled. The thickness of the workpiece decreases, the layers of wood on the concave side of the workpiece take on a wave-like shape from the indentation of the notch of the template, the outer layers are compacted. This contributes to an increase in the compression resistance of the concave layers in the wood and the stretching of the outer ones.
Bending with simultaneous pressing significantly improves the ability of wood to bend, allows you to bend wood with large knots located on the outside of the workpiece. It is used for bending softwood and soft hardwood.
Drying blanks after bending. Curved workpieces are dried in drying chambers to operational humidity, and the workpieces are placed in the chamber together with templates and tires covering them. The design of the drying chambers is similar to those used for drying lumber.
Dried blanks are unloaded from the chambers and sent to the cooling compartment, where they are kept for at least 48 hours to equalize internal stresses. Only after that, the blanks are freed from templates and tires and sent to the machining shop.
The sequence and principles of machining bent blanks on machine tools, i.e. giving them the final dimensions and a clean surface, do not fundamentally differ from the processing of straight blanks.
Production of bent glued parts. To obtain bent glued parts, hydrothermal treatment of wood before bending and drying after bending are not required. Bent glued parts are made from peeled veneer or plywood. The technological process for obtaining bent glued parts consists of preparing raw materials (veneer, plywood or thin strips), applying an adhesive solution to the glued surfaces, gluing blanks with simultaneous bending in molds or templates, and holding the parts after pressing to equalize moisture and stress.
Gluing is carried out either in blocks or in separate parts. Pressing is carried out in hydraulic presses with molds or templates. One of three types of heating of the pressed package is used: electrocontact, steam or high frequency currents (HFC). The most progressive heating HDTV. With this method, less pressing time is required and the temperature is more evenly distributed over the cross section of the package.
Adhesives based on carbamide resins of high concentration and high curing speed are used as a binder in the manufacture of bent glued parts. The consumption of such adhesives per 1 m 2 of the surface to be spread is 110-120 g.
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 necessary 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 whole products. In addition, when cutting out, a huge waste of material is obtained, which cannot be said about the method, at a time when 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 changing the shape of a dry wooden blank is a complicated process, since a dry tree can break, which is highly undesirable.
Having studied the technology of how to bend a tree, and the fundamental physical properties of wood, which allow you to change its shape and then save it, it is really possible to fully engage in wood bending at home.
Some features of working with wood
Bending wood is accompanied by its deformation, and compression of the inner layers and stretching of the outer. It is not uncommon for tensile forces to break the outer fibers. This can be prevented by preliminary hydrothermal treatment.
So, it is possible to bend 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 emphasized that birch veneer occupies approximately 60% of the total volume of bent-glued blanks.
When steaming the workpiece, the compressive property increases significantly, namely by a third, while the tensile property increases by only a couple of percent. And, therefore, thinking about whether it is possible to bend a tree thicker than 2 cm should not be a priori.
Heating in a steam box
First head to prepare a steam box. It may have been 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 located in the bottom of the box. In addition, a removable lid should be provided in the box, through which it will be possible to pull out a bent tree after it has bought the desired shape. In order to keep the wooden bent part in the desired shape, you should use clamps. They can be made independently from wood or purchased at a specialized store.
From wood, it is necessary to make round trimmings - a couple of pieces. Holes are drilled in them off-center. Then you need to push the bolts through them, and after that, drill another hole through the sides in order to push them tightly. Such simple crafts can become excellent clips.
Now it's time to steam the wood, for this we go to 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. At the end of the time, the tree must be removed from the box and given the desired shape. The process must be very fast. The workpiece is bent gently and gently.
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 reached, the bent tree must be fixed in this position. It is possible to fix the tree during its formation. That is why it is easier to control the process.
With chemical impregnation
In order to destroy the bonds of lignin between the fibers, it is possible to influence the tree with chemicals, and this can be done to the full extent at home. Ammonia is ideal for this. The workpiece is soaked in a 25% aqueous solution of ammonia. At the end of which, it becomes very obedient and elastic, which allows you to bend, twist it and squeeze out relief forms in it under pressure.
Ammonia is terrible! Based on this, when working with it, follow all safety rules. 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, it is necessary to leave it in such a 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 at the end of the evaporation of ammonia, the wood fibers will receive their former strength, and this will allow the workpiece to hold its shape!
Layering method
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 part. This is explained by the fact that the bend will shorten the lamellae. Before you start cutting, be sure to draw a diagonal line with a pencil. This must be done across the underside of the board. This will allow you to save the sequence of slats after they are 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 smallest transformation. A cork layer is applied to the mold. This will help avoid irregularities in the saw shape, which will allow for a sharper curve. 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 better to use urea-formaldehyde glue, which consists of 2 parts. It has a high level of adhesion, but dries for a long time. It is also possible to use epoxy resin in addition, but such a composition costs a lot, and not everyone can solve it for themselves. Ordinary wood glue cannot be used in this case. It dries quickly, but is very soft, which is not welcome in this environment.
The bent wood blank is guided as quickly as possible into the mold. So, another one is laid on a lamella smeared with glue. The process is repeated until the bent billet acquires the desired thickness. Boards are fastened together. After the glue is completely dry, go to shorten it to the desired length.
Drank like a way
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. be extremely careful, as 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. Perfectly 1.25 cm.
The cuts are made across the pattern of the wood. Then go to compress the edges of the workpiece so as to connect the resulting gaps together. This shape will be bought by the bend at the end of the work. After that, the bend is corrected. Much more often, the outer side is treated with veneer, in some cases with laminate. This effect allows you to correct the bend and hide any flaws made during production. The gaps between the bent tree are hidden elementarily - for this glue and sawdust are mixed, and at the end the gaps are filled with this mixture.
Regardless of the bending method, once the tree is out of shape, the bend will easily relax. In view of this, it needs to be done a little more in order to compensate for this effect later. The sawing method can be used when bending a part of a box or an iron corner.
So, using such simple tips, it is possible to bend a tree with your own hands without much effort.
It is difficult to make curved furniture frame designs, and the steep curves cut from straight sections of wood will require sophisticated manufacturing techniques to avoid short fiber weakness and large, uneconomical waste. However, complex curved shapes can be produced quite economically using dry or wet bending techniques, and since the fibers 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 a classic example of steam-curved furniture, and in the 1930s, glued laminated furniture became a high-fashion item with the invention of industrial methods for producing different grades of plywood. Both steam bending and layer bending can be done in the home workshop, and both methods continue to be used in the antique furniture industry and by skilled craftsmen.
steamed wood can bend with a relatively large bending steepness. The steam softens the wood fibers enough to bend them and mold them to the desired shape. It may take a lot of effort to bend, but this is quite achievable in a home workshop with basic equipment. You will need to make a template, a clamping collar and a steam chamber. Wood bending cannot be attributed to precise procedures. There are many options, and often trial and error is the only possible way to get the desired result.
Thin wooden blanks do not 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, for example, of a template), will take the form of a ring when freely bent if the ends of the workpiece are brought together. To obtain a greater bending steepness, the wood must be steamed and “hold” fixed on the template so that it, having taken the desired shape, stabilizes 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 chipping or breaking. The method described here is for bending relatively thick pieces of wood.
Wood preparation
For bending, choose straight-grained wood without knots and cracks. Any defect or shortcoming is potentially a weak point, so certain failures are possible. There are dozens of woods that are successfully steam-bent, and many of them are hardwoods. In the table below you can find a short list of suitable materials for bending. It is possible to bend well-dried wood, but freshly cut wood lends itself to such processing more easily. Atmospheric wood bends better than kiln- or kiln-dried wood. If the wood is too dry and difficult to process, you can soak it for several hours before steaming.
Depending on the type of workpiece, you can pre-cut it to size or do it with a saw, plow or scraper after bending. The latter method is often used in the production of bent furniture such as Windsor chairs and armchairs. Wood with a flat and smooth surface finish is less prone to delamination and will make finishing the entire piece easier. Raw wood shrinks more than seasoned wood, and when turned to bend, tends to take on an oval cross-section when dry. Regardless of the shape and size, make the length of the workpiece longer than the length of the finished product by approximately 100 mm. Then, in case of delamination or splitting of the ends after bending, it will be possible to cut off the damaged areas.
To calculate the length, make a drawing of the shape of the bend on a scale of 1: 1. Measure the outside of the curved part to get the correct length. This will allow you not to unnecessarily stretch the outer 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 form of a smaller inward bend.
The key to making a tight bend is the use of a flexible clamping collar. Make a mild steel collar 2 mm thick and at least as wide as the workpiece that is not already bent. This will work for just about any job you might need to do. To avoid possible contamination of the surface of the part as a result of the reactions of the interaction of chemical elements of wood, metal and the environment, make the clamp from 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 on the outside of the bent part from stretching and delamination. 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 abut against the stop with its entire surface. You can make them from a thick metal corner or from hard wood, which is usually easier to do.
To equip the clamp with reliable end stops, place wooden blocks approximately 225 mm long at the ends of the metal tape. On 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. In order for the clamp to have a convenient lever action for work, attach sufficiently strong wooden blocks to the ends of the strip on the back side of it using long stop bolts.
Template making
The steamed wood bends in a pattern that defines the shape of the curve and provides support for the fibers of the interior of the curved piece. The template must be of great strength and have a width at least equal to the width of the part to be bent. It must provide certain possibilities for fixing the workpiece on it with the help of clamps or other clamps.
You can make a template out of thick wood by setting the mold out of it on a base made of artificial wood materials, or use sheets of plywood glued together. Since bent wood tends to straighten out when the clamp is released, the shape of the template must be adjusted to account for the straightening of the part. To do this, you will have to use the most reliable, although not always pleasant way - the trial and error method to determine the parameters of such a correction.
Types of wood for steam bending
- 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 out of plywood for outdoor use, or use plastic or metal tubing. Plywood allows you to make a simple construction with glue and screws, exactly according to your specific requirements. This type of chamber is ideal if whole batches of wood are to be steamed. A plastic or metal tube chamber limits the size range, but is quite suitable for small workpieces.
Cut a piece of pipe of the required length in accordance with the dimensions of the workpiece. A length of 1 m is a convenient size that allows you to process entire workpieces or even parts of increased length, if you only need to bend its end part. Make removable plug-in end dampers out of plywood for outdoor use. Drill a hole in one of them for a steam pipe and with a planer cut off the lower part of the edge of the other damper to create a ventilation and drainage hole. Make special "open" shutters with a hole for long workpieces. Install wooden supports inside the corpse so that the workpiece does not touch the bottom of the chamber. Insulate the chamber with styrofoam or wooden blocks, securing them to the chamber with wire. Install the camera on stands with a slight slope so that condensation can flow out. Provide a reservoir for escaping water.
Steam can be generated using a small electric vaporizer or a factory-made steam generator, or you can make your own vaporizer from a 20-25L metal tank with a removable cap or stopper. Connect one end of a short rubber hose to a branch 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 up to 100°C. to ensure a constant supply of steam. Approximately the wood should be steamed for 1 hour for every 25 mm of thickness. Longer steaming will not necessarily improve the plasticity of the wood, but it can destroy its internal structure.
wood bending
You will only have a few minutes to fix the workpiece in the template before it starts to cool and stabilize. Prepare your workspace in advance. Have a sufficient number of clamps available and, in the case of processing very thick wood, arrange with a friend for help.
Shut off the steam supply and turn off the steam generator. Remove the workpiece from the chamber and place it in a pre-fitted and heated collar. Install it all together on a template. Fix the center by placing a piece of wood between the clamp and the clamp. With an interference fit, “wind” the workpiece onto the template and clamp it 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, keeping the material should take from 1 to 7 days.
Security measures
When bending with steaming, observe the following rules:
- Do not overtighten the lid or plug of the steam generator.
- Ensure that the steam chamber is well ventilated.
- Do not let the steam generator run without water.
- Do not stand or lean over the steam generator and steam chamber when opening them.
- Wear thick gloves or mittens when handling heated workpiece and steaming equipment.
- The source of steam must be removed at a considerable distance from flammable objects to materials.
One of the ways of processing blanks of joinery is bending. The wooden blanks treated with hot steam are able to bend and, after drying, retain the resulting shape. Such a 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 softens under the influence of high temperature, and after cooling, it again holds the fibers together. This is the basis for the bending process. It should be borne in mind that wood of different species lends itself to bending in its own way. For bent products, it is best to use oak, beech, birch, yew, cherry, elm. But pine, spruce, cedar, alder should not be used for these purposes.
Work on bent parts begins with the choice of material. The blanks must be straight-grained, the use of wood with curved fibers is not allowed. The prepared material is dried in natural conditions, under sheds, to a moisture content of not more than 20%. But artificially dried wood should not be used for bending, since it lends itself worse 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 hardwoods such as oak, ash, beech.
It is best to use a steam chamber to heat the blanks before bending. It is easy to make such a camera at home using a plastic pipe of suitable sizes and an ordinary kettle. Parts are placed in a pipe, and steam is supplied from a kettle. The exposure time in the chamber depends on the size of the part and is determined empirically. In this case, you can be guided by the fact that 1 cm of the thickness of the workpiece requires 30-40 minutes of steaming the wood.
In places of bending on the parts, if the design of the product allows, you can slightly reduce the thickness of the material, chamfer. 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 fixing. It should be borne in mind that after the wood has warmed up, there will be very little time to fix the workpiece, no more than 5 minutes. Therefore, everything must be done quickly, but if the part begins to cool, then it should be heated again. Otherwise, you can break the workpiece.
Therefore, it is important to provide such a design of molds and clamps that would allow you to quickly fix the workpiece in the desired position. If the forms are made of wood, then they should not be coated with any protective compounds, painted, varnished. Firstly, they deteriorate from heating, and secondly, they will interfere with the drying of the blanks.
Short blanks are bent on mandrels of a larger radius, and then fixed in the mold. This pre-bending reduces the chance that the part will break when the bend is formed. It is necessary to keep the parts in the form until completely dry so that they do not straighten back. This usually takes 6 to 9 days, and is determined empirically.
After releasing the workpiece from the clamps, it must be postponed for a day, and only then proceed to processing and finishing. This is necessary in order to remove residual extensor stresses. The tips are simple, but they will allow you to easily master the process of how to bend wood.