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 a plastic pipe suitable sizes and a 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 blanks are bent on mandrels of a larger radius, and then secured in a mold. 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.
Bending is one of the methods for making beautiful and durable wood parts, for example, for furniture. For the home handyman It is quite possible to master such technology. A bent part is much stronger than a sawn part, less wood is consumed in its production, and the sawn surfaces produce half-end and end cuts, which complicate further processing and finishing of parts.There are three ways to bend wood. One of them, the most famous, involves preliminary steaming of wood and then giving it the required shape in powerful presses. This hot way bending is used mainly in mass production, for example, of chairs.
Along with it, especially at home, two other methods of bending wood are practiced, but in a cold state.
The maximum bending radius depends on the depth of the cuts (and, accordingly, on the thickness of the workpieces), the distance between them and the flexibility of the wood. The cuts are made both parallel and perpendicular to the fibers. This work operation is performed using a miter saw or a hand-held circular saw with a guide stop. If not special tool, an ordinary hacksaw for wood is also suitable. The main thing is that the depth of the cuts is the same.
At wood bending fibers on inside compress, and on the outside - stretch. Wood “tolerates” fiber compression relatively easily, especially if it is pre-steamed. It is almost impossible to stretch it.
Flexibility also depends on the type of wood and the thickness of the workpieces. For example, hard wood from temperate climate zones - beech, oak, ash, elm - is easier to bend than tropical wood species (mahogany, teak, sipo, etc.). Conifers are too tough for this.
The resistance value of bent wood until it breaks is determined by the ratio 1:50, i.e. The bending radius must be at least 50 times the thickness of the workpiece. For example, a workpiece with a thickness of 25 mm requires a radius of at least 1250 mm. The thinner the wood, the easier it bends. Therefore, where possible, it is advisable to make a part of the appropriate shape by bending (Fig. 1).
In this method, individual strips of wood of the same thickness and width are glued, laid in several layers so that their grains are parallel, and placed in a mold made of hardwood. The matrix and the mold punch are compressed with clamps and the bag is left in this position until the glue dries.
The thickness of the strips glued to each other can vary between 1-6 mm, again depending on the required bending radius. Cold-curing glue is suitable for gluing layers. If bent-glued blanks are intended for use in external structures, it is best to use waterproof glue.
To determine the permissible thickness of the veneer strips or planks to be bent (with a larger thickness, the wood may break), you need to know the smallest bending radius. The wood is most deformed on the inside of the bend. Therefore, it is always necessary to measure here.
As an auxiliary device, it is advisable to use a template that you can make yourself. To determine the bending radius, we take an ordinary school compass and draw on tracing paper several circles (with a slight increase in their radius) having general center. As a result, we get a template. We apply it to the surface of the bend, for example, a mold, and move it until we find a suitable circle largest diameter. We measure its radius on a template. We divide the resulting value by 50. The quotient of the division will be the maximum allowable thickness of the strip of plank or veneer.
When working with molds, the bend on the outside of the workpiece should be smoother than on the inside. In this case, we draw two circles from one center, the radii of which differ by the total thickness of the strip material.
The most difficult situation is when it is necessary to bend a part of a complex configuration with different bending radii. Here the bends are for internal or outside blanks can be constructed freely if its shape is not tied to the contours of any piece of furniture.
In this case, the line for the second cut (the first one is at the beginning of the bend) can be constructed like this. Using a compass, measure the total thickness of the layers to be glued, draw a circle with it on hard cardboard, cut out a circle and apply it in several places to the line of the first cut. At the same time, we apply the circle so that it is in contact with the first line, and draw its outline on the opposite side, respectively. The second cut line will be the end-to-end connection between these auxiliary lines.
When determining the number of cuts to be made on a workpiece for bending along a known radius (it also depends on the width of the groove and the type of wood), we use an auxiliary structure. To do this, we take a block similar to the workpiece (Fig. 2). We cut out one single cut on it with a depth of 2/3-3/4 of the thickness of the block. Draw a straight line on a sheet of paper and mark the cut point on it.
We place the block on the paper so that its lower edge before the cut coincides with the drawn line and the marked point of the cut, and fasten the block with a clamp to the work table. We set aside the distance of the required radius b on the line and the block and bend the block until the upper edges of the cut meet. The distance a between the end of the line and the mark on the block will be the distance between the individual cuts that can be marked on the workpiece.
If cuts need to be filed on the outside of the workpiece, the distance between them and, accordingly, their number are determined in the same way. We bend the workpiece as much as the elasticity of the wood allows. If the test piece of wood breaks, then this can be expected from the workpiece fixed in the mold.
Based on materials from the magazine "Do It Yourself"
Wood is recognized as one of the safest materials for human health used in construction and in the manufacture of various furniture. Its environmental friendliness can be rated five points, which significantly expands the scope of use wooden products. Wood can be used to produce workpieces of various shapes and sizes. Special ones help with this. These technologies also include wood bending and gluing, which is widely used in the modern production cycle.
The entire woodworking process takes a significant amount of time. First the wood - all this happens in wood processing enterprises. Subsequently, boards and other materials are prepared from wood.
These blanks are sent to factories, where they are specially made from them. Construction Materials or various furniture. During the production process, wooden blanks of different shapes and sizes may be required, and therefore woodworking techniques such as bending and gluing are widely used.
Bonding is used to produce parts of the desired size and shape. Wood splicing can be done by width, length or thickness. Pre-prepared ends of the workpieces can have special grooves or tenons, which increases the strength of the parts being connected. Different types of wood glue are used in the gluing process.
Wood bending is necessary to produce curved parts. You can bend wood manually, subject to certain features of this work, or 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 rated at five points. Woodworking factories always try to follow all the technology of working with wood, and therefore the goods produced are of high quality.
Photos of the wood processing methods described above
Splicing Gluing Bending
Gluing is the main process of working with wood on any furniture production. In order to obtain a durable and high-quality workpiece, it is necessary to strictly adhere to the entire technology of the process of connecting individual parts. The accuracy of all work is also necessary to prevent possible subsequent deformation.
The process of joining wood and products made from it consists of several stages:
Preliminary preparation of wooden blocks and other workpieces consists of creating special tenons or grooves in them, which can be done using a special tool - a milling cutter.
Milling is a fairly old branch of wood processing. The first milling machines appeared more than three centuries ago. Today, milling is an indispensable and universal method of wood processing.
For this woodworking machine, you can choose cutters of different shapes - sharpened elements with different types of blades. Using these cutters, various parts are made.
In the gluing process, milling machines are necessary for:
Milling machines are used everywhere, they can be either manual or electric. Ease of manufacture wooden blanks for gluing using a machine can be estimated at four points. In order to obtain an accurate workpiece, you first need to gain some experience.
This video provides an overview of cutters for splicing wood and making technological connections. Milling cutters shown for straight and corner splice, as well as microthorn, zigzag and wave cutters:
Splicing lumber in any production allows you to create high-strength materials with new, sought-after qualities and also allows you to rationally manage production waste.
Automatic splicing lines include several sequentially operating machines, which ultimately make it possible to obtain the material of the required length and width from short blanks. With the help of a splicing line, glued laminated timber, which is popular today, is produced.
The entire technological process when using a production line for splicing wooden blanks consists of several stages, which are provided by a complex of machines included in the installation:
Using a splice line on furniture factories provides high productivity, reduces the number of jobs. , obtained using automatic machines, can be rated five points, since the entire process is strictly controlled.
This is how it works automatic line length splices:
The correct selection of the type of glue determines the quality of joining wooden workpieces. The choice of glue also depends on the type of wood being glued and the shape of the workpieces. Waterproof adhesive compositions are most often used.
IN furniture industry Several types of synthetic adhesives are used:
Bonding of parts is carried out coldly and by heating them. To glue workpieces along the edges, adhesive film is often used; it comes in sheets of various sizes.
Before gluing, the parts must first be prepared, that is, degreased, removed dirt and different kinds spots After applying glue over the entire surface and connecting the required workpieces, the parts are clamped using special devices, which are removed only when completely dry.
To splice glued wood, special machines in the form of presses can be used. They clamp the parts for the required time. This ensures a strong connection between the adhesive surfaces and prevents movement of parts. The press can be selected according to the length of the beam, power, and the presence of additional functions.
Wood gluing may sometimes be required at home. This often happens when wooden furniture sets are put up or due to various breakdowns. Before gluing, the surfaces of wooden products must be properly prepared.
To do this, their pores are cleaned of old glue and paint layers, degreased with a solvent, and dried. After applying glue to both parts, they are carefully connected and clamped in a clamp for at least 30 minutes.
Commonly used adhesives include:
In order to achieve high strength of the parts to be glued, it is necessary to strictly follow the instructions included with each type of glue.
You can clearly see how wood is glued together in the video:
Wood bending can be defined as the process of bending layered or solid pieces of wood to give them the desired curved shape. Bending technology is based on plastic qualities different types wood Curvilinear wooden parts can also be obtained by processing on special machines, but this method is rarely used, as it is endowed with a number of negative consequences.
Hardwood such as oak, beech, and ash has greater plasticity. Therefore, mainly the species of these trees are used for the manufacture of curved parts. There are cold and hot bending of wood.
Hot bending is based on sharp increase plasticity of wooden blanks when heated from 80 to 120 degrees. This heating mode is achieved by boiling in water or steaming.
The wooden blanks plasticized in this way are bent according to the prepared template and secured with clamps, after which they are cooled and dried. When bending, the convex side is stretched to the required level, and the concave side is compressed. Thick workpieces are bent using special machines.
Cold bending is used to produce multilayer curved bent parts. To obtain a part of the desired shape, you need to place several blanks coated with glue on top of each other, give them the required shape and, using a press machine, wait the required time. The shape of blanks obtained by cold bending is retained longer.
This video will show you how curved wood is made:
Wood bending at home begins with the choice of material. The prepared parts must be straight-layered; they must first be dried under natural conditions. You also need to soak parts if they are made of ash, oak, or beech. Before bending, the workpieces must be steamed.
To do this, you can use a steam chamber prepared yourself. To make such a device, a pipe and a boiling kettle are suitable, from which steam will continuously flow into this chamber through hoses.
The holding time of the blanks can only be determined experimentally, but it is believed that in order to achieve the required plasticity, it is necessary that one centimeter of wood in thickness be steamed for 30 to 40 minutes. It is also not worth overexposing the product.
Before you start bending, you need to prepare the mold and clamps. After heating the wood, it can be bent well only for 5-10 minutes, so everything needs to be done extremely quickly. The products are kept in the mold until they are completely dry, usually this takes at least one week. You can then process 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 the products is significantly reduced and this can be rated five points. But the labor intensity of the entire process takes a lot of time, and therefore only truly passionate people can take up bending wooden blanks and their subsequent use.
Examples of interior elements made from bentwood
Headboard Rocking chair Table Decorative element Chairs
Bending wood using steam. Or how to bend strong, unbending oak into the shape you need without any problems.
I have been working with flexible wood for 13 years now and during this time I have built many steaming chambers and tested them in action. different systems steam generation. What you are reading now is based on reading literature and personal practical experience. Even mostly from experience. I usually worked with oak and mahogany (mahogany). I had to deal a little with thin birch veneer. I haven’t tried other breeds because I build and repair boats. Therefore, I cannot judge with authority the work with other species such as cedar, pine, poplar, etc. And since I haven’t done this myself, I can’t judge it. I write here only about what I experienced personally, and not just what I read in a book.
After this introduction, let's get down to business...
To begin with, there are a few basic rules that are always followed.
By steaming wood to bend it, you soften the hemicellulose. Cellulose is a polymer that behaves like thermoplastic resins. (Thanks to John MacKenzie for the last two suggestions).
To do this, you need heat and steam at the same time. I know that in Asia people bend wood over a fire, but that wood is definitely quite wet - usually freshly cut. Shipbuilders in ancient Scandinavia prepared hull materials for their ships and placed them in a saltwater swamp so that they would remain flexible until they were ready for use. However, we are not always able to obtain freshly harvested wood for these purposes, and excellent results can be achieved by using ordinary wood. air drying. It would be very good if, a few days before the operation itself, you immerse the workpieces in water so that they gain moisture - those Vikings knew what they were doing. You need warmth and you need moisture.
The main rule concerns steaming time: one hour for every inch of wood thickness.
As I discovered, along with the probability of understeaming the workpiece, there is also the probability of oversteaming it. If you hovered an inch board for an hour and when you tried to bend it, it cracked, do not conclude that the time was not enough. There are other influencing factors that explain this, but we'll get to those later. Steaming the same workpiece for a longer time will not give a positive result. In such a situation, it’s a good idea to have a workpiece of the same thickness as that intended for bending and which you don’t mind. Preferably from the same board. They need to be steamed together and after the supposedly required time, take out a test sample and try to bend it into shape. If it cracks, then let the main workpiece steam for another ten minutes. But no more.
Wood:
Usually, the best option it will if you can find freshly cut wood. I understand that the cabinet makers will shudder at these words. But the fact remains that fresh wood bends better than dry wood. I can take a six-foot-long plank of white oak, clamp one end of it in the workbench, and bend it to whatever curvature I need—that's how malleable the fresh wood is. However, naturally, it will not remain in this state and you will still have to float it.
In shipbuilding, the main evil is rot. If you are concerned about this issue, then please note that the very fact of steaming fresh wood eliminates its tendency to rot. Therefore, you don’t have to worry - the frames of boats are usually made from fresh steam-bent oak and do not rot if it is taken care of. This also means that in this way it is possible to make at least blanks for the Windsor Chair. However, I also worked a lot with air-dried oak and the result was also excellent.
When selecting wood for bending, one thing to avoid is cross-layering. When trying to bend such a workpiece may burst.
Therefore, regarding wood moisture content, the rules are as follows:
If all you have is from the dryer and you can’t get anything else - well, then you have no choice. I dealt with this too. But still, if you can get air-dried wood, it will be much better. Just last week I bent 20mm thick walnut boards for the transom of my yacht. The blanks were dried for several years and their bending went completely smoothly.
Steaming chambers.
It is absolutely useless, and even harmful for the bending result, to strive to make an absolutely sealed chamber. The steam must leave it. If you do not provide steam flow through the chamber, you will not be able to bend the workpiece and the result will be as if you steamed it for only five minutes. After all my experiences, this is familiar to me.
Cameras come in a variety of shapes and sizes. It should be large enough so that the workpiece seems to be suspended and steam flows around all sides of it. A good result will be obtained from pine boards with a cross-section of about 50 x 200. One way to ensure the “hanging” of the workpiece is to drill through holes in the side walls of the chamber and drive round wooden rods from hardwood into them. With their help, the workpiece will not touch the bottom and the area of closed wood will be minimal. However, you should not make the chamber so large that the amount of steam generated is not enough to fill its volume. The chamber should be such that it is humid inside and the steam rolls in waves. This means that the dimensions of the chamber must correspond to the capabilities of the steam generator (or vice versa).
When I needed to bend a five-meter mahogany board with a cross-section of about 200 x 20 for the new deckhouse of my yacht, I made a chamber from pine boards with a cross-section of 50 x 300. A 20-liter metal tank acted as a steam generator. The energy source was a propane torch. The thing is absolutely wonderful because it is convenient and mobile. Capacity 45000 BTU (1 BTU ~ 1 kJ). This is an aluminum cylinder with three legs and one burner with a diameter of 200 mm.
I recently found a 160,000 BTU propane burner in the West Marine catalog for $50 and purchased that as well. With its help I can bend frames even for "Constitution".
When I say one hour of steaming per inch of thickness, I mean one hour of SERIOUS CONTINUOUS steaming. Therefore, the boiler must be designed to provide steam for the required time. I used a new 20-liter fuel container for these purposes. Workpieces can only be placed in the chamber when the installation has reached full capacity and the chamber is completely filled with steam. We must absolutely ensure that the water does not run out prematurely. If this happens and you have to add water, it is better to give it up. Adding cold water will slow down steam generation.
One way to make the most of the water is to position the chamber at a slight angle so that the condensed water inside flows back into the boiler. But at the same time, it is necessary that the fitting through which the steam enters inside is closer to the far wall. Another way is to make a siphon system to ensure that its level is replenished as the water boils away.
Here's what a photo of such a system looks like:
In the picture you see a wooden camera located slightly at an angle. Directly below it is the steam generator boiler. They are connected to each other via a hose from the radiator. If you look closely, you can see an L-shaped pipe coming out of the base of the boiler on the left. It’s hard to see in the photo, but its vertical part is actually translucent and this way we will know about the water level inside the boiler. To the left of the boiler you can see a white bucket containing water for make-up. Take a closer look and you will notice a brown tube connecting the bucket to the vertical part of the pipe - the level gauge. Since the bucket is located on a hill, a siphon effect is observed: as the water level in the main boiler drops, water enters it from the bucket. You can add it from time to time, but do this extremely carefully so that it does not rush quickly into the boiler and cool it too much.
To minimize the need to add water during the steaming process, it is better to start work with a bucket filled to the top. I myself prefer to leave a small air gap in the boiler.
Many chambers have a door at the end through which workpieces can be moved if necessary and removed if necessary. For example, if you are engaged in the manufacture of bent frames and you would like to complete this as much as possible in a day, you melt the boiler and (when reaching full power) put the first workpiece inside. After 15 minutes, add the second one. After another 15 - the third and so on. When it's time for the first one, you take it out and bend it. I'm assuming this procedure will take less than 15 minutes. When she sits still, the second one is already on the way... etc. This allows you to get a lot of work done and avoid over-steaming.
The door has another important function. It doesn't even have to be made of hard material - on my small camera, just a hanging rag serves for this purpose. I say "hanging" because the steam must emanate outward from the end (since a stream of steam is needed). We must not allow what will happen in the cell overpressure, making it difficult for steam to enter. And besides, the picture itself wooden box, from which steam pours out in clouds, looks quite cool - passers-by are simply dumbfounded. The second purpose of the door is to prevent cold air from entering the chamber from below the workpieces.
So, we will assume that our wood is boiling (with a pleasant smell) and the templates are ready. Try to organize everything in such a way that the operation of removing the workpiece from the chamber and bending it goes quickly and smoothly. Time is of the essence here. You have only a few seconds to do this. As soon as the wood is ready, quickly take it out and immediately bend it. As fast as human dexterity allows. If pressing to the template takes time, just bend by hand (if possible). For the frames of my yacht (which have a double curvature), I took the blanks out of the chamber, stuck one end into the clamp and bent this end and then the other just by hand. Try to provide more bend than is necessary for the template, but not much. And only then attach it to the template.
But I repeat once again - the wood must be given curvature immediately - within the first five seconds. With every second the wood cools, it becomes less pliable.
The length of the blanks and the curvature at the ends.
It is practically impossible to produce blanks of exact length and expect to be able to achieve a bend at the ends. You simply don't have the strength to do it. For this reason, if you need a piece one meter long, but its thickness is more than 6 mm, you are better off cutting a piece about two meters long and bending it. I'm just going by the assumption that you're not in the workshop. hydraulic press- I definitely don’t have one myself. When cutting out a workpiece with a margin, remember that the shorter it is, the more difficult it will be to bend.
And if it is with a reserve, then the end of the real part will have a large curvature - with 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 areas and to take into account the required thickness when choosing the material.
Templates.
After steaming the workpiece and clamping it onto the template, you must wait a day for complete cooling. When the clamps are removed from the workpiece, it straightens somewhat. The extent of this depends on the structure and type of wood - it is difficult to say in advance. If the workpiece already has some natural bend in the desired direction, which can be taken advantage of (I try to do so whenever possible), the degree of straightening will be less. Therefore, if you require a certain curvature in the final product, the template must have more curvature.
How much bigger?
Here we are dealing with pure black magic and I personally cannot give you any numbers. One thing I know for sure: it is incomparably easier to straighten an excessively bent workpiece than to bend a cold, unbent one (provided that you do not have a giant lever).
Warning. If you bend workpieces for lamination, the template must be exactly the shape of the workpiece in the laminate - I have rarely had cases of large bending of well-bent laminated wood.
There are endless options for bending templates. And it doesn’t matter at all which one you choose if you happen to be the owner of a clamp factory - you can never have too many of them. If wood with a thickness of more than 12 mm is bent, the template must have significant mechanical strength- he will experience quite high loads. You can see what it looks like in the photo at the beginning of the article.
Quite often, when bending, people use a metal strip on the outside of the bend. This helps to evenly distribute stress along the length of the workpiece and avoid cracks. This is especially true if the outside fibers are located at an angle to the surface.
Well, that’s probably all my thoughts for now.
