Bend Plywood

Creative home woodworking projects frequently involve more than flat surfaces and 90-degree angles. Learning to bend plywood is an important first step if you are planning to create a product that will have curved, rounded or contoured surfaces. Each method of bending plywood has its benefits and drawbacks.

Steps

Choosing your best bending approach

  1. Select the kerfing method when the inside of the bend will not be visible and when the bent plywood will not be subjected to substantial force.
    • This is a quick and easy method of bending plywood.
    • This method is only appropriate when the concave (or inner) surface of the bend is either not visible or is subsequently laminated.
    • Kerfing weakens the plywood and should only be used where the bent surface of the plywood will not be supporting weight. For instance, kerfing is not an appropriate method for bending plywood to make a skateboard ramp.
  2. Consider steaming the plywood to bend it when both sides of the bend will be visible.
    • Steaming produces a finished piece that is stronger than one produced with kerf cuts.
    • This method requires the construction of a steam box and a form. It will also take more time to complete than kerfing and requires care to avoid burns.
  3. Consider laminating and bending several thin pieces of plywood when strength of the final piece is a primary consideration.
    • Like steaming, laminating several thin pieces of plywood together requires the construction of a form. It also takes more time than kerfing and requires more equipment, but it will produce the strongest result.

Cutting a series of kerfs

  1. Measure and mark the positions on the plywood were the bend will begin and end.
  2. Inspect both sides of the plywood between these 2 marks for knots. A knot, especially on the finished (uncut) side, will likely result in failure when the plywood is bent.
  3. Set the cutting depth of the blade of your circular saw to 1/2 to 2/3 of the thickness of the plywood.
  4. Use a large square or straight edge as a saw guide and cut a series of kerfs (grooves) approximately 1/4�inch (6 mm) apart on the back side of the plywood.
  5. Bend the wood into position and secure it.
  6. Fill the kerfs with wood glue. You can fill them with wood glue before bending the plywood if the kerfs will not be accessible once the plywood is bent and secured into position.

Steaming the plywood

  1. Choose a piece of plywood that is knot free.
  2. Build a form by cutting the profile of the bend in several pieces of MDF (medium density fiberboard) or similar material with a jigsaw. Attach these pieces in a stack until you achieve the necessary thickness for your form.
  3. Build a steam box. See http://www.instructables.com/id/How-to-make-a-steambox-for-bending-wood/ for details.
  4. Place the plywood on the wire supports in the steam box.
  5. Turn on the heat source for the steam box and steam the plywood for approximately 1 hour per inch (24 mm) of plywood thickness.
  6. Put on heavy gloves, then remove the plywood from the steam box and immediately bend it over your form. Attach clamps to hold the plywood on the form.
  7. Leave the plywood clamped to the form until it is thoroughly dry.

Laminating several thin pieces of plywood together

  1. Build a form as described in the instructions for bending steamed plywood.
  2. Select a thin sheet of plywood such as 5.2 mm thick birch.
  3. Cut enough pieces from your plywood sheet to stack to your desired thickness.
  4. Precondition the plywood strips and determine the clamp spacing.
    • Stack you pieces without gluing them and clamp them to the form, attaching the first clamp in the middle of the plywood stack.
    • Attach additional clamps working from the middle out to each end.
    • Use enough clamps to eliminate any spaces between the plywood and the form. This will condition the plywood pieces so they bend more easily during the final bending.
  5. Remove the clamps.
  6. Select a glue with a long open time (such as a polyurethane glue or a urea formaldehyde glue).
  7. Apply the glue to each plywood piece so the entire surface of each is covered.
  8. Stack the plywood pieces and clamp them to the form in the same manner used during the conditioning step.
  9. Leave the plywood stack clamped until the glue cures. This time varies depending on the type of glue used.
  10. Sand or trim the edges of your finished piece to remove dried excess glue and to achieve the desired final surface finish.

Soaking the plywood

  1. Soak plywood in water for about 2 hours. Or soak until the plywood is softened.
  2. Stick soft plywood in a bench vise.
  3. Bend the plywood with clamps or your preferred method (choose from above).
    • Note: You must bend the plywood along the grain so that it is stronger and does not snap.
  4. Leave to dry for a couple of hours.



Tips

  • If you have a band saw, make your form by gluing several pieces of MDF together, then cutting the bend profile in the MDF block you've created. This will create a 2-piece form. Press your steamed or laminated plywood over one piece of the form and then clamp the second piece of the form over the plywood.

Warnings

  • The steam from a steam box and plywood removed from a steam box can scald you. Always use heavy gloves when loading or unloading the steam box and when handling wood that has been removed from the steam box.

Things You'll Need

  • Pencil
  • Plywood
  • Circular saw
  • Large square or straight edge
  • Wood glue
  • MDF (medium density fiberboard)
  • Jigsaw or band saw
  • Steam box
  • Heavy gloves
  • Bar clamps
  • Polyurethane or urea formaldehyde glue
  • Sander and sandpaper

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Sources and Citations

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