Few people know that bending plywood is a very common operation in carpentry; even fewer craftsmen are familiar with correct technique execution. We propose to consider the features of this material and its behavior when bending, as well as the basic techniques and devices for bending plywood at home.
Features of plywood behavior when bending
The veneer from which plywood is made is nothing more than a set of elongated fibers. They are rigid and durable, the space between them is filled with a soft binder. To give the sheets additional strength and compensate for warping in plywood layers, veneer has different grain directions in adjacent layers. Due to this, plywood is a rigid material that is difficult to bend.
Typically, plywood with an even number of veneer layers is used for bending, that is, it does not have a predominant fiber direction. Otherwise, you should calculate the direction of bending across the minimum number of longitudinal fibers, or vice versa - along, if the part is required to have increased strength.
The thinner the plywood, the easier it is to bend. Sheets with three layers bend easily across the grain of the outer layer even when cold
When the fibers are parallel to the fold line, they do not interfere with the curvature of the plane. However, layers located transversely experience significant loads. Typically, the fibers can stretch quite strongly; the conditions necessary for this are provided by their softening due to heating or moistening.
At the same time, the layers located on the inner radius of bending experience compressive loads, which are not compensated by the elasticity of the material. If the bend is steep enough, folds may form on its inner side. Sometimes the stress in this area is high enough to cause delamination—rupture of the adhesive layer or even the fibers themselves. This characteristic behavior can be compensated for by a number of technical techniques, which are the focus of this article.
Required tools and equipment
As always, it’s impossible to do without high-quality equipment and tools. Since the basic technology involves softening the sheet, molding it, and then drying it in an immobilized position to take its shape, bending requires at least a set of clamps. Ideally, there should be at least a dozen of them, but you can bend the plywood in stages, rearranging the fasteners.
In this case, along each line across the bend, the workpiece is fixed in three places: at the highest point of the radius and at the edges. In other words, with due diligence you can get by with six clamps, but keep in mind that the accuracy of the dimensions of the finished part may be significantly lower than required.
Plywood bending is almost always done using templates. The exception is sheets of arbitrary radius, which are pre-bent before sheathing frame structures. For risers of stairs, chairs, armchairs and other pieces of furniture, the shape of the bent parts is known with high accuracy. Therefore, you first need to make a spatial figure to which the softened sheet will be attached while it dries and takes on the required shape.
There are quite a few types of equipment that provide technologically advanced steaming or soaking of glue. Humidity and temperature must be kept within acceptable limits, otherwise the glue may irreversibly lose its strength properties. At home and for one-time work, you can use calorific heaters or films for heated floors. Wetting is best done not directly, but through a hygroscopic material that can accumulate and gradually release moisture, for example through foam rubber, hemp burlap or felt. It also helps to have all the adjustable tensioning and compression devices available, such as lashing straps or hand jacks.
Bending and soaking
When bending plywood it acts important rule: The higher the thickness of the sheet and the steeper the bending radius, the more effort it will take to soften. If you do not take into account the difference in the quality of plywood, then after soaking you can achieve a bending radius of the order of 50-70 times the sheet thickness. For steeper bends, other methods are recommended.
Soaking or steaming has the goal of softening the fibers in the veneer and making the glue more flexible with the expectation that after drying it will set and securely fix new uniform details. At the same time, oversaturation of wood with water, as well as sudden wetting and drying, is not permissible.
The easiest way to soften small sheets of thin plywood is in a steam bath in a regular saucepan or in a juice evaporator
For proper soaking, plywood must be kept in conditions of relative humidity of about 90-100% for 2 to 12 hours, depending on the thickness. Periodically you need to check if there is any delamination of the veneer at the ends or swelling in the center. From time to time you can attempt bending. If the part takes shape relatively easily and no cracking is heard, then all that remains is to firmly fix the plywood until it dries completely.
For long parts it is easier to prepare a box from any suitable material and then soften with steam from the steam generator
Wetting is recommended when the plywood is laid on a flat base and wrapped on each side with a layer of absorbent material. If the workpiece is not tightly wrapped in film, you should monitor the humidity level and periodically re-spray the burlap with water. Heating to 50-60ºС during wetting helps speed up the process and make the swelling of the glue reversible. It is strictly forbidden to allow plywood to overheat, so you should constantly monitor the temperature.
An alternative to softening by wetting is steaming the plywood. In this case, the sheet is fixed above a container of boiling water or near it. The disadvantage of this method is that the humidity rises throughout the room with concomitant condensation. The advantage of this method is uniform softening and a low risk of overmoistening or overheating.
A vacuum table speeds up the process of softening plywood, as well as subsequent molding according to a template
A softened sheet of plywood is used to cover the pre-prepared frame structure or template, fixed at key points of each bend. The plywood is pressed using clamps or self-tapping screws with a washer sequentially from one edge to the other, and the more often the temporary fastener is installed, and the stiffer it is, the lower the likelihood that the part will change shape after removal from the template.
Machining methods
In some cases, there is no point in resorting to softening: for example, if the part is fixed to a sufficiently rigid frame, it will take the desired shape over time due to natural changes in humidity. Another special case is the need to bend plywood to a radius that is less than permissible for a certain thickness. Here it is worth using both softening of the sheet and its mechanical processing.
One of the processing methods before bending is applying to inner side bending a series of cuts parallel to the folding axis. It is better to make cuts with a cone cutter using a linear guide. The depth of the grooves should be no more than 3/4 of the thickness of the workpiece, and in the end at least two layers of veneer should remain intact.
If the cuts face the inside of the part and are hidden from view, there is no point in calculating their number and pitch. Subsequently formed scars can, if necessary, be leveled with automotive putty and sanded to a smooth state. With due diligence, it is possible to calculate the reduction in the length of the arc during bending, using a known angle and radius of bending. In this case, the number of cuts will be equal to the quotient of the arc reduction divided by the thickness of the cutter in the widest part of the entry. The required number of cuts must be evenly distributed over the entire bend radius.
Before fixing on the template, the cuts formed on the plywood are filled high-quality glue for wood, for example Titebond 2. Protruding glue can be immediately removed with a spatula or sanded after drying. While the glue hardens, the plywood is firmly fixed to the template.
You can also make it easier to soften thick plywood by perforating the workpiece. Holes with a diameter of 2-3 plywood thicknesses are made using a core cutter or Forstner drill in checkerboard pattern with a pitch of about 80-100 mm between them. The degree of perforation can be greater; this is determined both by the flexibility of plywood to bend and by the required final strength of the part. Naturally, this bending method is only suitable for hidden technological elements that do not form a finishing plane. If desired, the bent part can be sheathed on one or both sides with veneer or thin plywood, having previously softened them.
Bending according to templates
In the simplest case, the role of a template can be played by pieces of hard plywood shaped like a bending profile. Since most parts are bent along the same contour on both sides, the templates are made in pairs and then fastened together with spacers slightly smaller than the width of the part. Templates can also be different if you need to bend the part irregular shape, that is, curved along two axes.
Another type of template is a frame made of beams that does not form an exact bending contour. In this case cross beams located at the pressure points, that is, on the most protruding and concave parts of the part profile. For fastening at intermediate points, you can add an arbitrary number of jumpers to the frame.
When making the frame, you need to take into account the type of clamping devices used. Thus, plywood inserts can have holes for the jaws of clamps, and the frame itself can be equipped with additional stiffening ribs in the direction of pressure and tensile loads. If the part has a uniform bend along its entire length, it can be fixed without a frame, for example, tied with a rope, cable, chain with a screw tow bar, or using sling belts.
Manufacturing of composite parts
You can bend parts of complex shapes by alternately gluing layers of steamed veneer onto a workpiece of the required shape. In practice, this is a method to avoid fiddling with thick parts, because on sharp bends it is much easier to deal with thin sheets due to the small values of the permissible radius.
In the simplest case, the base is formed by a relatively thick perforated sheet of plywood, the permissible bending radius of which is obviously lower than the required one. Such a part, most likely, will not have the necessary strength, so it is subsequently “sheathed” with several more thin layers. In each case, an adhesive connection is made over the entire plane; the sheets are pre-softened so that they do not straighten the shape of the core.
Sheathing can be done not only for the purpose of imparting strength. In some cases, one or more outer layers serve a purely decorative function. For example, thin sheets of veneer can hide traces of attaching the workpiece to the template, and plywood will disguise perforations or cuts. It is also possible to paste the part with plastic, laminated veneer and other finishing materials that do not retain their shape well.
Plywood is made up of slabs of natural veneer glued together and is one of the most common lumber today. This popularity is due to its high strength and, at the same time, ease of processing. Its use has found application in furniture production, construction, shipbuilding, design and other industries. One of the most important properties of plywood is its ability to change shape as a result of bending. This process seems complicated only at first glance, but even a non-specialist can master how to bend plywood.
Advantages of plywood
The material is not scary high humidity and changes in ambient temperature. In addition, it is distinguished following features, talking about undeniable advantages over natural wood in some cases:
- high strength;
- durability and wear resistance;
- ease of processing and installation;
- combined with other building materials;
- There are no cracks, including through ones.
The main differences between lumber are related to the type of wood from which they are made, therefore, when purchasing material, it is necessary to take into account the subsequent scope of its application.
Classification
Speaking about the classification of such material as plywood, it should be noted that there are four grades of this lumber.
- The first grade is the best. However, it is also the most expensive. It is distinguished by a minimum of flaws and deformations.
- A second grade product allows for minor defects such as cracks and knots.
- The third grade is distinguished by the presence of numerous defects, both of the wood itself and of the lumber itself, such as leakage of the adhesive layer and the presence of inserts.
- Fourth grade lumber is suitable only for the manufacture of packaging containers. However, it is also the cheapest, as it has greatest number all kinds of defects.
Flexibility of plywood
Plywood has a very high flexural strength coefficient. For this reason, bending is one of the main processing methods. Bent plywood is widely used in products.
Easy to bend plywood sheet directly depends on its thickness. Thin sheets are easier to bend, thick sheets are more difficult. In this case, the material bends better along the fibers than across, and the bending angle in this case is the largest. We will look at how to bend plywood in the production of various products below. Currently, several methods for this technological process are known.
Method using heating or steaming
Before bending the sheet, it must be thoroughly heated using steam. A steam iron or a tank of boiling water may be suitable for this. If necessary, the sheet can be impregnated hot water. Processing time directly depends on the thickness of the material and the temperature of the steam or boiling water. However, steaming for too long can lead to the destruction of the adhesive layer and delamination of the plywood.
Having steamed the sheet, it is bent in the desired configuration, after which this position is fixed with any available material, for example, rope. The sheet is fixed until completely dry and takes the desired shape.
Method by sawing and notching
This method is used when the thickness of the plywood sheet does not exceed 22 mm. It consists of creating conical cuts on the surface of the material with a depth of no more than half the thickness of the sheet. It is advisable to do them using milling machine, since another method may lead to cracks and splits.
Having made the necessary cuts, we bend and fix the sheet, treat the surface with glue and apply a sheet of veneer. Leave the product in this position for 24 hours.
Bonding method
Before bending plywood in this way, a pattern is made. Next, the sheet is bent along it, smeared with glue and a new sheet of plywood is applied. In this case, the directions of the fibers should alternate. Having glued the layers, we fix them with clamps and leave them for about a day. After this, the workpiece is subject to the grinding process. This is done in order to remove any remaining glue and give the product a beautiful appearance.
It should be noted that after processing, products should not be stored in damp areas.
There are cases when you can use special thin (3-4 mm) plywood, specifically designed for bending. It is used in the production of products such as arches in doorways.
How to bend sheets of plywood without a machine
To bend plywood, two conditions must be met: moisture and heat. There is also a dry way to change its shape. You can work with material of any thickness, but the thicker it is, the more time it takes to achieve the result. Bent plywood is used in construction to construct arches, spiral staircases etc.
What kind of plywood can be bent?
Thin layers of wood are glued together, arranged in different directions. As a result, the fibers of one layer have a direction of 45º, 60º, 90º with respect to the fibers of adjacent layers. This method of making plywood increases its bending resistance, so it is easier to bend material with a small number of layers. In production it is bent using special equipment, clamping in the matrices. It is pre-treated with steam and thereby acquires sufficient elasticity.
During renovation or private construction, a bent plywood structure may be needed. Then you have to make do with improvised means. But even in this case, the work can be done efficiently if you follow the technology.
Methods for heating plywood
Heating can be done in the following ways:
- ferry,
- in hot water.
Without heating, the work can be done using epoxy glue.
Hot water should be poured into a bathtub or other suitable large container. The workpiece is immersed in it for about half an hour, as a result the layers of wood are steamed. IN living conditions steam is created using a boiling kettle. Some experienced craftsmen heat up plywood using an iron. The steam supply must be constant, otherwise the wood will cool quickly.
Securing the workpiece
Moistened plywood easily changes shape, but if the bend angle is large, the work is done in stages. The wood is bent to a small angle, dried, then the steps are repeated as many times as possible until the required shape is achieved. If the bend angle is small, you can do it in one go. The next step is to secure the plywood, which can be done in 2 ways:
- the load is installed at the bend, the ends are tied with a rope and supports are installed under them;
- Fastening to the template is done using tape or rope.
In the second case, any curved structure made of rigid material can act as a template. The most commonly used is fiberboard. To make an arch, steamed wood can be secured in the opening using self-tapping screws. Some nuances of steaming wood should be taken into account: in very hot water it can delaminate, so it is important not to overexpose it. A thin layer can steam in 5 minutes. You can use another option: iron the workpiece moistened with water with a hot iron. After this, immediately give the required shape, repeat wetting and heating with an iron.
Watch a video about bending using a ready-made template at the end of the article.
A metal template made of durable steel is also used to secure the plywood, but it bends along with it. This technique is preferable for large parts with complex configurations. The steel strip is tied to the plywood until it is moistened, then its shape is changed. The steel template is untied only after the wood has completely dried.
If a weight is used to secure the plywood, it is important that its width is equal to the width of the workpiece. If it is smaller, only that part of the wood that is equal to the width of the load will bend. Changing the shape of plywood is carried out independently when its thickness is up to 20 mm. It should be taken into account that different breeds Woods have different abilities to bend and unbend. Compression can be performed by 30%, stretching by 2%. Walnut, beech, and ash show good results. Maple, oak, and larch are difficult to change shape.
How to bend large sheets?
It is not always possible to treat a very large sheet with steam. In this case, so-called cuts are made. They are strips that are shaped like a cone. A manual milling machine is used. The cuts must be made to the opposite layer, it is important not to catch it, otherwise the material will split. For wood 4 mm thick, the cutting depth is 2 mm.
The steeper the bend radius, the greater the number of cuts. The plywood should then be clamped onto the template, and a thin layer of veneer glued to the outside of it. The glue used is epoxy or PVA. Drying time: approximately 1 day. Thus, the workpiece is hollow at the bend, but can withstand heavy loads.
Very often, in the process of producing furniture or some other plywood products, it becomes necessary to create elements of irregular shapes. Of course, such blanks can be cut from a single sheet, however, in this case, an unreasonably large consumption of material results. There is another way to give wood the desired bends; in this article we will talk about how to bend plywood.
First, let's figure out what plywood is. These are thin sheets of wood glued together in such a way that the fibers of each layer are located in different directions. This method of producing the material makes it more durable, but also increases bending resistance. That is why it is easiest to bend plywood that has few layers. For industrial production For furniture, this material is bent in a special way: the sheet is clamped in dies, treated with steam, and then bent using special equipment. If you want to produce your own wooden part irregular shape, there are several ways to do this: gluing layers, steaming or making cuts. Below we will take a closer look at each of the methods. Steaming the materialProcessing processBefore bending 10 mm thick plywood, it must be treated with hot steam. You can do this yourself as follows:
If you have a large enough container into which you can place the fragment to be processed, you have the opportunity to boil the plywood. To make it easier for you to determine right time for similar processing, use the table below:
If you don't have a suitable vessel on hand, you can simply wet the plywood. To do this, place a sheet of material in a bath of water and leave for a while. The soaking period can be determined based on the thickness of the wood, the direction and angle of bending. It should also be noted that when soaking the material in hot water (over 60°C), the processing time will be 2 times longer than when boiling. If you use cold water, the soaking time will increase by at least 20 times. Please note that you should not steam the plywood for too long, otherwise the layers of wood may separate from each other. After the material has lain in the water for a sufficient time, it is bent into in the right place and fix it until the part is completely dry. Please note that the greatest degree of bending can only be done if you bend the sheet across the wood fibers. We also note that if you process the material yourself, you can combine steaming with soaking. In this case, only the place that is subsequently supposed to be bent is held above the steam.
Securing the partNote that you can give the desired shape to a part in one or more stages. It depends on how steep the bend angle needs to be. If this indicator is large enough, then the necessary manipulations should be carried out in several stages. After soaking or steaming, the plywood sheet is slightly bent and left until completely dry. After this, similar work is carried out again and again until the desired shape is achieved. If the angle of curvature is small, then you can cope with the task in one stage. After you have completed all the necessary manipulations with the wood, the bent plywood should be secured. This is done in two ways:
As such a template, you can use any suitable structure that has the required curvature and sufficient strength. Very often, for such purposes, a template is made from fiberboard sheets. If you want to make a part in the form of an arch from plywood, a steamed fragment of material can be fixed in doorway using self-tapping screws. If there is a need to create a part of large size and complex shape, it is best to use a template made from a steel sheet. In this case, the workpiece should be bent together with the plywood, fastening both materials together. You can separate the steel element from the wooden one only after the latter has completely dried.
Bend plywood by notchingIn this paragraph we will look at how to bend thick plywood. As a rule, the notching method is used when processing material with a thickness of 16-22 mm. The fact is that it is quite difficult to steam or soak such a sheet, so special cuts are made in those areas where it is supposed to create curvature. They have a cone-shaped shape and are made using a manual milling machine. You should know that the sheet can only be cut to the layer with fibers in the opposite direction, otherwise the material may crack. Creating cuts of different widths allows you to change the bending angle of the product. After the cuts are made, the part is bent as required and fixed in this position. Then a sheet of veneer is glued on top using epoxy glue or PVA, after which the workpiece is left to dry completely. The product can be bent either by cutting inwards or outwards.
Gluing plywoodIn order to create a product with a certain bend from plywood, you first need to make a template. After this, a thin sheet of material is bent according to the pattern, and the same is done with the following layers. It is important to remember that each new sheet of wood must be laid on the previous one, alternating the directions of the fibers. You can glue the layers together using PVA or epoxy glue. After the part has completely dried, its ends must be processed grinder, eliminating irregularities and fragments of dried leaked glue. Furniture made of bent plywood, photo:
To make beautiful and quality product, it is necessary to take into account some subtleties:
In this article we have described everything available methods thanks to which you can bend plywood with my own hands using available means and tools.
How to bend plywood, video: |
Very often during the construction or renovation of houses there is a need to obtain curved surfaces of plywood sheets.
In construction, repair or furniture making, there is a need to bend plywood and obtain curved surfaces.
This raises the question: how to bend plywood so that the bend is strong and does not crack? You can perform this procedure yourself.
Bending at home
When bending wood, there are a number of difficulties that are associated with the structure of the material, as well as technological features of this process:
The thinner the plywood sheets, the better and easier it is to bend them.
- The thinner the material, the easier it is to work with. However, it is necessary to take into account the fact that to construct, for example, an arch, the plywood must have a thickness of at least 10 mm. That is, you need to bend an already quite thick puff pastry.
- When making plywood, the layers of veneer are located at different angles to each other. This is done in order to increase the bending resistance of the material.
There are several ways to bend plywood at home, the most popular of which are:
- humidification (steaming);
- incision;
- gluing.
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Steaming
In workshops and special workshops, bending and the required curvature are achieved quite simply. To do this, the part is saturated with steam, after which it comes under the influence of a special vice, which bends it to the desired radius of curvature.
At home, this procedure is quite difficult to carry out, since it is very difficult to find a suitable container with constantly boiling water. Therefore, only small pieces of plywood can be bent in this way. To do this, you can use an iron with a steam function or hold the material over a container of boiling liquid for a certain time.
An alternative to steaming is to dampen the plywood. To do this, pour into a container of the required dimensions (for example, into a bathroom) hot water, after which the workpiece is immersed in it for a certain time, which depends on the direction of bending and the thickness of the sheet. Below is a table for calculating the boiling time of plywood at a temperature of about 95°C.
| Three-layer plywood, mm | Five-layer plywood, mm | Time for bending along the fibers, min | Time for bending across the fibers, min | ||
| 1,0 | 15-20 | 10-15 | 1,0 | 60-90 | 60-90 |
| 1,5 | 20-40 | 15-20 | 1,5 | 90-120 | 90-120 |
| 2,0 | 40-60 | 20-30 | 2,0 | 120-150 | 120 |
| 2,5 | 60-90 | 60 | 2,5 | 150-180 | 120 |
| 3,0 | 90-120 | 90-120 | 3,0 | 180-210 | 150 |
| 4,0 | 180 | 120 | 4,0 | 240-300 | 180-240 |
As a result of this procedure, the layers of wood are steamed. After steaming, the wood is bent by a small angle and fixed in this position in several ways:
- a load is placed in place of the bend, the ends of the plywood sheet are tied together with a rope, and supports are mounted under them;
- The plywood is fixed in a prepared template, to which it is attached using rope or tape.
Then the workpiece is dried and used for its intended purpose. Steamed plywood easily changes shape, but if you need to create a large bending angle, then such work should be done in stages. Therefore, all procedures are repeated as many times as necessary to achieve the required bending value.
An alternative to steaming is to soak the plywood in warm or cold water. In this case, you should take into account:
- for soaking at a water temperature of 60°C, the time must be increased by 1.5-2 times;
- for soaking at a liquid temperature of 20-30°C, the time increases by 15-20 times.