Few people know that plywood bending (how to bend plywood?) is a very common operation in woodworking; even fewer craftsmen are familiar with the correct technique.
We recommend considering the characteristics of this material and its performance when bent, as well as the basic technology and equipment for bending plywood at home. .
Modeling wood is undoubtedly one of the most refined processes that can be carried out on this material.
The curve, in fact, gives the wood a particular silhouette, enriches its appearance and allows the creation of furniture or small pieces of furniture of great value and beauty.
The bent wood with the technical right and skill it remains robust and strong like the right and sometimes assumes a particular tension which helps to stiffen the whole structure.
There are many systems available to perform a temporary or permanent bending of wood, how to bend plywood without breaking it?
Let’s see together how to bend plywood in a few simple steps and achieve an excellent result.
How to bend plywood without breaking it?
- Method 1: strips of wood, pencil, glue and circular saw
- Method 2: Model with thorns, strips of wood
- Method 3: Hammam, wooden strips, tongs
Curve in the sculptures. This is the simplest system that allows to obtain a curvature of wood, even quite narrow, but only suitable for the manufacture of decorative elements, since the resistance of the curve is quite limited.
We do this by making a series of cuts perpendicular to the curvature we want to achieve, with a depth of about 2/3 the thickness of the axis itself.
The grooves (i.e. the notches), which should start before the point at which the bend begins and end soon after, should be made with a circular saw with a steel blade fitted with thick teeth, as it is essential to remove at least 3-4 mm each cut.
Once this phase is completed, the wood is ready to be folded: we do this slowly and gradually, coming back several times to allow the fibers to expand without breaking.
Just fill the grooves with vinyl glue and fix the part on a jig until it is completely hardened.
Fold the wood using the template with thorns. This tool consists of a solid wood (or multilayer wood) plate with a minimum thickness of 18 to 20 mm in which are made a series of holes with a diameter of approximately 16 to 20 mm, in rows and ordered columns.
The second essential item to use is a piece of wood with a curved side and a rectangular shape. To shape the plywood, we need to bend the strip against the die and keep it curved using two or more pins inserted into the top holes.
This method allows you to define curves of different radii, while creating multiple matrices can significantly reduce the radii of curvature. Other types of jigs, suitable for very thin plywood blades or even Steam shaping.
First of all, you should know that steam bending is the one that allows us to achieve the best results, but it is not as convenient as the methods described above.
Also Read : How To Bend Wood with Steam at Home 4 Easy Steps
In any case, with a little? of patience and skill in DIY, we can always achieve this very special technique.
To begin with, we will need to have a steam chamber that will allow us to soften and bend the wood using only water vapor; if we don’t have one, we can build the boiler by following the tutorial given in this link.
Now we turn on the boiler and put the strips of plywood inside (it is important to spray the wood for about 1 hour every 3 cm of thickness).
Once the necessary time has elapsed, remove it from the chamber and lock it in the jig with pliers as soon as possible, that is, immediately after removing it from the boiler.
Finally, let sit until the plywood panel is completely dry.
Characteristics of plywood when bent
The veneer made of plywood is nothing more than a set of stretched fibers. They are strong and durable, and the space between them is filled with a soft adhesive.
In order to give the board extra strength and to compensate for the war-page in the plywood layer, the veneer has different grain directions in adjacent layers. Therefore, plywood is a hard material that is difficult to bend. .
Generally, the number of veneer layers of plywood is an even number, that is, it does not have a main fiber direction.
In the opposite case, if increased strength is required, the bending direction should be calculated on the minimum number of longitudinal fibers, and vice versa.
The more thinner the plywood, the easier it is to bend it. The three-layer sheet is easy to bend on the outer fibers even in cold conditions.
When the fibers are parallel to the fold line, they will not interfere with the curvature of the plane. However, the straddled layers are subject to great stress.
The characteristic is that the fibers can be stretched very strongly, and the conditions required for this are provided by softening due to heating or wetting. .
At the same time, the layer located at the inner bending radius bears a compressive load, which cannot be compensated by the elasticity of the material.
If the bend is steep enough, creases may form on the inside of the bend.
Sometimes, the stress at this time is high enough to cause delamination-the adhesive layer or even the fiber itself breaks.
This characteristic behavior can be compensated by a variety of techniques discussed in this article.
Tools and equipment required
As always, you can’t live without high-quality equipment and tools.
Since the main technique involves softening the sheet, shaping it, and then drying and shaping it in a fixed position, at least a set of clamps are required to bend it.
Ideally, there should be at least twelve, but you can bend the plywood in stages to rearrange the fasteners.
In this case, fix the workpiece in three positions along each line of the bend: the highest point of the radius and the edge.
In other words, through due diligence, you can use six fixtures, but keep in mind that the accuracy of observing the dimensions of the finished part may be much lower than required.
Plywood is almost always bent according to the template. The exception is sheets of arbitrary radius, which are pre-curved before covering the frame structure.
For the risers of stairs, chairs, armchairs and other furniture, the shape of the curved part is known to have high precision.
Therefore, it is first necessary to make a spatial pattern that attaches the softened sheet to it while being dried and having a desired shape. .
There are many types of equipment that provide technical steam or glue immersion functions. Humidity and temperature must be kept within acceptable limits, otherwise the glue may irreversibly lose its strength properties.
You can use an air heater or floor heating film at home and one-time work.
It is best not to wet it directly, but to use a moisture-absorbing material that can accumulate and gradually release water, such as foam rubber, sack or felt.
In addition, it also includes all available adjustable drawing and squeezing aids, such as lashing straps or manual jacks.
Bend and soak
When bending plywood, an important rule should be followed: the greater the thickness of the board, the steeper the bending radius, the greater the trouble of softening.
If we do not consider the difference in the quality of the plywood, it is possible to reach a bending radius of the order of 50-70 sheet thickness after soaking. For tighter elbows, other methods are recommended. .
The purpose of soaking or cooking is to soften the fibers in the veneer and make the glue more plastic, and it is expected that the new shape of the part can be grasped and firmly fixed after drying.
At the same time, do not allow the wood to be over saturated with water and to wet and dry rapidly.
Small pieces of thin plywood are most easily softened in a steam bath in a regular pan or juicer.
In order to properly soak, depending on the thickness, the plywood must be kept at a relative humidity of approximately 90-100% for 2 to 12 hours.
Regularly check whether there is a de-lamination of the veneer at the end or whether the center is raised.
You can try bending from time to time. If the part is relatively easy to form and no cracking sound can be heard at the same time, just fix the plywood firmly until it is completely dry. .
For longer parts, it is easier to prepare a box suitable for any material and then soften it with steam from a steam generator.
When the plywood is placed on a flat base and wrapped with an absorbent material on each side, it is recommended to wet it.
If the workpiece is not tightly wrapped in the film at the same time, the humidity should be controlled and water should be sprayed on the linen regularly.
Is it heated to 50-60 during wetting? С helps to speed up the process and make the glue swell reversible. Plywood is absolutely impossible to overheat, so you should constantly monitor the temperature.
An alternative to wetting and softening is to steam plywood. In this case, the sheet is fixed on the boiling water container or not far away.
The disadvantage of this method is that the humidity rises throughout the room and is accompanied by condensation.
The advantage of this method is that the softening is uniform, and the risk of water stains or overheating is not easy to occur. .
The vacuum table speeds up the softening process of the plywood and performs subsequent molding according to the template
The pre-prepared frame structure or template is covered with softened plywood and fixed at each key point of the bend.
The plywood is clamped from one edge to the other with clamps or self-tapping screws with washers.
The more temporary fasteners are installed and the stronger, the less likely the parts will be deformed after being removed from the template.
In some cases, it does not make sense to resort to softening: for example, if a part is fixed to a sufficiently rigid frame, it will end up in the desired shape due to natural changes in moisture.
Another special case is the need to bend the plywood to a radius less than the allowable thickness of a certain thickness. Here it is worthwhile to use both the softening and machining of the sheet.
One method of pre-bending is to make a series of cuts parallel to the roll axis on the inside of the bend. It is best to use tapered cutters with linear guides for cutting.
The depth of the groove should not be greater than 3/4 of the thickness of the workpiece, so at least two veneer layers should remain intact.
If the cut faces the inside of the part and is not visible, it is meaningless to calculate its number and spacing. If necessary, car fillers can be used to smooth the scars that are formed later, and then sand to a smooth state.
Through due diligence, you can use the known bending angle and radius to calculate the reduction in arc length during the bending process.
In this case, the number of cuts will be equal to the quotient of the arc reduction divided by the tool thickness in the widest part of the entrance.
The number of cuts required must be evenly distributed across the entire bending radius.
Before fixing on the template, the cuts formed on the plywood should be filled with high-quality wood glue, such as Titebond2.
The protruding glue can be removed immediately with a spatula, or sanded after drying. After the glue is cured, the plywood is firmly fixed on the template.
You can also easily soften thick plywood by punching holes in the work-piece. Holes with a diameter of 2–3 times the thickness of the plywood are made in a checkerboard pattern using a slotting machine or a Forstner drill, and the steps between them are about 80–100 mm.
The degree of perforation may be higher, depending on the flexibility of the plywood bending and the required final strength of the part.
Naturally, this bending method is only suitable for hidden process elements that do not form a finishing plane.
If necessary, the curved part can be sheathed with veneer or thin plywood on one or both sides, and soften them in advance.
Bending by template
In the simplest case, the role of the template can be completed by a rigid plywood with a curved contour shape.
Since most parts are bent along a contour on both sides, the templates are made in pairs and then fixed together with spacers slightly smaller than the width of the parts.
If you need to bend a part of an irregular shape (ie bend along two axes), the template can also be different.
Another type of formwork is a frame made of beams, which does not form a precise curved contour.
In this case, the beam is located at the pressure point, that is, on the most convex and concave part of the part profile.
To fix it at the midpoint, you can add any number of jumpers to the frame.
When making the frame, the type of clamping device used must be considered.
Therefore, on the plywood insert, holes can be provided for the jaws of the clamp, and the frame itself can be equipped with additional reinforcing ribs in the direction of clamping and tensile load.
If the parts have uniform curvature over the entire length, they can be fixed without using a frame, for example, with ropes, cables, chains with screw hooks or using lifting straps to fasten them.
Manufacturing of composite parts
By alternately bonding the transpired plywood layers to the workpiece of the desired shape, parts with complex shapes can be bent.
In practice, this is a way to avoid fiddling with thick parts, because in large bends, it is much easier to handle thin plates due to the smaller allowable radius.
In the simplest case, the base is made of relatively thick perforated plywood, and its allowable bending radius is significantly lower than the required bending radius.
Such details probably won’t have the necessary strength, so they are subsequently “covered” with more thin layers.
In each case, it is necessary to bond on the entire plane, and then pre-soften these sheets to avoid straightening the shape of the core.
Sheathing can only be done for the purpose of enhancing strength.
In some cases, one or more outer layers have a purely decorative function. For example, a thin veneer can conceal the traces of fixing the work-piece on the template, while plywood can conceal perforations or cuts.
It can also be pasted on the part with plastic, laminated sheet and other facing materials that cannot maintain the shape well.
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