bending plywood, woodworker

Bending Plywood

Curved panels have always been a part of fine furniture, cabinetry and architectural trim. Considerably harder and therefore more expensive than flat panels, curved panels are one of the things woodworkers use to distinguish their fine quality work from more mundane woodworking. While not all fine woodworking includes curved panels, enough does that we can easily make this distinction, seeing it as something associated with only the finest work.

Part of what makes furnishings and architecture made with curved panels to be considered to be amongst the best, is how infrequently it is seen. This is in part due to the high labor cost in making such pieces, but it is also related to the rarity of people who know how to do this type of work. Making bent panels is much more complicated than bentwood strips, such as would be used on a bentwood rocker.

Whether you’re building a chair, constructing a skateboard ramp, working on a model, or making columns for your home, bending plywood might be part of the process. There are several different ways to bend plywood. The best method to use depends partly on the size of your project, partly on the type and thickness of the plywood being used, and partly on the resources you have available.

How much bend you can get out of a particular piece of plywood depends a lot on the type of plywood you are using, as well as its thickness. Obviously, thinner plywood is going to be more flexible than thicker sheets. Plywood products which are designed specifically for bending will often have a tighter bend radius than other types of plywood, even if the other plywood is just as thin.

How to Bend Plywood

When bending plywood sheets, it’s always better to use multiple thin sheets and bond them together, rather than using one thicker sheet. This process takes a bit longer but it creates less problems and provides visually pleasing results – perfect for furniture and other projects where appearance is a primary concern. Baltic birch is an excellent plywood choice for this.

Whichever of the following plywood bending methods you choose, ensure that you work slowly. This allows the wood’s fibers to stretch gradually, reducing the risk of cracking or breaking.

Bending Plywood in Molds

Perhaps the easiest way to bend plywood panels is to steal the same idea used for making the aforementioned bentwood rocker. That’s to use a mold for bending the plywood. When doing this, it’s necessary to make the mold stronger than the plywood to be bent, as the plywood will be clamped to the mold as it sets into its new form.

Start by building your mold to match the finished dimension you would like for your piece. MDF is a good product to use for this purpose as it is strong enough to keep the plywood contained. But back the MDF up with heavier structural pieces, to hold it in place.

Cut pieces of thin plywood to fit inside the molds. It’s a good idea to make your plywood pieces longer than needed and trim off excess later. Working quickly, place your plywood strips into the molds one at a time. Cover the top of each strip with a generous layer of wood glue before adding the next strip of wood. Do not use construction adhesive for this. Clamp the mold together tightly and allow the plywood to set for 8 to 24 hours, until you are sure the glue is fully dried. The actual time will depend on size and shape.

Kerf Bending Plywood

The name of this method comes from the saw kerf used to give stiff sheets of plywood the ability to bend. This is one exception to the bending plywood thickness “rule” about choosing the thinnest sheets possible. You can kerf bend plywood over ½” thick fairly easily.

The idea is to make a series of cuts into the back side of the plywood, so that there is room for the sheet’s overall size to compress into the space made by the cuts, making the curve possible. Locating the cuts carefully is essential, as that will affect where your curve is in the overall piece. Combining kerf bending with straight sections allows you to make pieces with rounded corners.

Choose plywood for kerf bending carefully: Birch or Baltic birch is an excellent choice. Softwood plywoods do not work well for this. Nor can you use this method on OSB and other engineered plywood products. Use an online kerf spacing calculator to determine how many cuts you’ll need to make and how far apart to space the cuts for kerf bending.

Once you’re confident that your calculations are correct, use a radial arm saw or table saw to cut the kerf slots in the plywood, from the back side. These cuts need to be almost all the way through the plywood, stopping just short of the face veneer. If the cuts are too shallow, your plywood won’t bend successfully; if they’re too deep, the piece will break rather than bend. It’s a good idea to make at least one test bend on a scrap piece of wood if you have one available, before trying to cut your finished piece.

When you’re ready to bend, fill the cuts with wood glue and carefully bend your piece into the desired shape. It can be helpful to make this bend around any end piece or filler pieces that will be used with the curved piece, in order to ensure a good fit. Push the splines into place and allow ample time for curing – a week is ideal for items like tables and chairs. When finished, sand the glue and use wood filler to conceal it before finishing your project as desired.

You can also buy plywood that is already cut for kerf bending. This is ideal for architectural columns or other large projects which have a large amount of curvature in them. It eliminates the need for cutting the kerf yourself, which is almost impossible for such large pieces, without the availability of a cabinet saw, with extensions. Plywood pre-cut for kerf bending will be cut the full length of the sheet, with the exception of only a small amount of plywood at each end.

Bending Plywood with Steam

You might think that steam bending plywood is the way to go for all kinds of projects, but this method is best for small pieces such as model parts. The reason for this is that unless you have a huge vessel that you can maintain at a steaming hot temperature, it’s impossible to maintain moisture and heat long enough to adequately steam large pieces (think a cabinet door) of plywood for bending.

Start by deciding how to mold your wood once it comes out of the steamer. Create a mold out of 2x4s, clamps, and cut mold pieces, to give you the finished shape you want. You don’t need the mold to provide the full contour, merely to hold the plywood in that contour. As long as you have enough structural elements in your mold to guarantee that curve, there is no need for a top piece for the plywood to be bent to. You’ll want this set up, before steaming the plywood, so you can go straight from the steamer to the shaping form you’ve chosen.

Next, set up your steamer pot. Wear a pair of heat-resistant gloves, and insert your plywood into the steamer basket. Cover the pot with a lid and allow the wood to steam for an hour per inch of thickness. If your wood is 1/8 inch thick, it should steam for about 7 ½ minutes.

When the plywood is ready to come out of the steamer, don your gloves again. Carefully remove the wood and manipulate it onto your molds as desired. Clamp it into place and leave it to dry completely.

Heat Bending Plywood

Heat bending is commonly used on musical instruments made of wood, such as guitars and violins. While that is usually solid wood and not plywood, the same methodology works for both. In this, you will be using a combination of water and heat, allowing you to bend some types of plywood. While fir and pine don’t respond well to this method, birch, poplar, and mahogany often turn out very well.

You’ll need a source of heat for bending the plywood. While some people use hot towels, that’s actually more akin to steam bending, than heat bending. While using steam in conjunction with heat is effective, pure heat bending consists of heat only.

While you can buy bending heaters, you can easily make your own out of metal pipe or even a coffee can (metal obviously). Make sure that the outer surface is smooth, as otherwise it will imprint on the wood you are bending. A propane torch, of the type used for sweating copper plumbing fittings, works well as a heat source for your bender. Make a sturdy metal mount to hold your can or pipe, as well as the torch, with the flame centered in the opening.

To bend a piece of plywood, start by building a mold with MDF, or simply create a frame with 2x4s. The method for building your mold or frame will vary depending on the type of project you’re working on, as well as the size of the plywood you’re planning to bend. As with steam bending, it is not necessary to have a mold with full surface contact, as long as it will hold the workpiece in the desired shape.

You’ll also want a pattern to use while bending the plywood, so that you can see if you are close to the right curve. If your mold is easy to get the plywood piece onto and off of, it can serve as the pattern as well; but if not, a piece of scrap plywood or cardboard, with the contour drawn on it, works well.

Lay your plywood flat and mark a crease line where you’ll be applying pressure to bend the wood. Turn on the torch and heat up the bender. Once hot, lay the workpiece on the bender, wearing heavy, heat-resistant gloves. Heat the plywood, using your hands to put pressure on it and bend it.

Once the wood is bent to the right shape, lay it into your mold and clamp it in place. Then soak towels in water and heat them in the microwave or dip them in boiling water. Lay them on the workpiece and clamp the whole thing together.

How to Bend Plywood for a Skate Ramp

It’s surprisingly easy to bend plywood for a skate ramp. The amount of bend or curve you need in the plywood is gradual enough that you don’t need to use any special bending techniques. Ordinary plywood products can be used and you don’t need any heat source.

Start by using an online ramp tool to calculate dimensions and determine which supplies to purchase. Note that the best plywood for skate ramps is 3/8” or thinner. Once you have built your frame according to specs, lay your plywood onto the frame. Start from the bottom. Get friends to stand on the plywood and bend it gradually as you carefully screw it onto the frame. If you like, you can get the plywood wet before you start – but this means that you’ll have to wait for it to dry completely before applying a weather-resistant finish.

bending plywood, woodworker
Bending plywood, Theron Burger

Bending Plywood in Two Directions

You can use any of the methods outlined above to bend plywood in two or more directions… at least to some extent. While it is possible to do a compound bend in plywood, you have to realize that what you are trying to do requires that there be more material in the center of the bend, than there is on the outsides. So you are limited.

Work slowly, set up your molds and/or braces ahead of time, and make your calculations carefully. If possible, try your bending process with a piece of scrap wood before moving on to your main project. It’s worth noting that bendable plywood might be best for projects that call for multiple bends in different directions, as this product is designed specifically for the purpose of bending.

Choosing Bendable Plywood

While it’s possible to put a mild curve in most types of plywood, not all plywood is truly bendable. Spend a little time looking into the different products available for your specific project to determine which one will be best. If you’re working on a model, an art installation, or a piece of furniture, it’s a good idea to look into products labeled as “flexible board” or “bending plywood.” These types of bendable plywood are designed to flex in different directions without cracking, and they can take on the shape of nearly any contour.

Aviation plywood is a good choice for projects that require bending. Originally created for building airplanes during World War II, aviation plywood is used mostly for model making today. Thin and flexible, it is made without any voids, like marine grade plywood. This is preferable for bent projects, as there are no gaps in the core to cause uneven bends.

In addition, you can look for bendable plywood products such as Radius bending plywood, which can bend in cross-grain directions as well as long-grain directions. These products are the most versatile of all. They come in a variety of thicknesses, and will provide you with the appearance you desire.

Uses for Bendable Plywood

Bendable plywood is amazing stuff, and once you start using it, you might find yourself looking for more excuses to add projects to your list. Here are some great ways to use bendable plywood in your next project:

  • Create curved columns
  • Make decorative arches
  • Build furniture
  • Build unique cabinetry faces

It’s worth noting that thin, decorative bendable plywood isn’t typically suitable for exterior use. Reserve this specialty product for interior projects.

Bonus Shortcut: Try Pre-Curved Plywood

If you’re in a hurry or you lack the appropriate tools for bending plywood, don’t despair. Pre-curved plywood comes in a vast variety of configurations large and small alike, so you can complete your project with far less effort. If you aren’t able to find pre-curved plywood locally, a quick search will yield several online sources to choose from.

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