Introduction: Bentwood Birdhouse
Building birdhouses is one of those classic things to do with your hands. We are first exposed to the process in high school wood class. Frustrating moments with poorly fitting plywood and nails usually end any interest in the project. This is a new twist on the design for these usually dull construction projects that will actually look good on the outside of your house this summer and involves fun construction techniques uncommon for this type of project.
The process uses bendable poplar wood plywood that is made in Italy and is available at most specialty wood shops assembled in a composite epoxy-coated structure that is light, waterproof and elegant.
Step 1: Gather Materials
Bendable Poplar plywood 4x8 sheet--about $35
West System 105-B Epoxy Resin 32 ounces
West System 206-B Slow Hardener 27 ounces
Craftsman or RotoZip Cutter tool with 1/8 " rotary blade for wood
Razor blade knife with utility blade
Shirt cardboard 4 pieces 8"x12"
Elmers Carpenters wood filler--interior/exterior
Hot glue gun
Sandpaper or sanding block
Bits: 1/4" 1 1/2"
Step 2: Modeling the Birdhouse
This birdhouse design is a simple arrangement of four pieces of 8"x12" bendable poplar plywood. I began with a model of the construction made up of 4 pieces of shirt cardboard--a construction material that I remember fondly from my childhood. These are still available from your shirts if you have them boxed and laundered otherwise you can cut them out of "store bought" cardboard. The roof and the floor consist of identical cut designs that hold the curved sides in place. The curved cuts in the cardboard model should be centered mirror images of each other and should not extend further than 1/2" from the edges of the cardboard. The type of curve you draw and model are up to you but the curve must be long enough to accomodate the length of the side pieces. In the model you can cut the slits with a razor-knife in the poplar you will be cutting the slits with a 1/8" rotozip bit that will allow the plywood to slip in.
Step 3: Cutting the Pieces
There is a natural curve to the panel of plywood and the four identical pieces of poplar plywood required in each birdhouse all should curve in their long dimension. The 8" x12" pieces can be easily marked out on the large sheet so that you should get 6 pieces out of the 48" side of the sheet. The plywood is easily cut with a straightedge and a razor knife.
Step 4: Drawing the Cuts
The inspiration for the design of the birdhouse came from a wing shape that I had in my mind. I used a curve tool to get the shape I wanted and cut a piece of wood to use in tracing the line on the poplar plywood pieces. The lines were drawn so that they stopped 1/2" from the ends of the plywood and were mirrored across the long axis of the piece staying an inch away at the ends. Other similar cuts can work and you can experiment with the design. Both the roof and the floor piece are drawn out in the exact same way.
Step 5: Cutting the Groove
I usually cut both marked top and bottom at one time--if building multiple houses you can cut four of these sheets at one time. It is best to clamp the sheets securely before cutting. I drill start and stop holes at the end of each line with a 1/4" bit and then proceed to cut out the long channels with the rotozip or craftsman equivalent rotary drill with the 1/8" bit. This will form the tight slot that will hold the wall pieces in place. It takes a little practice to get a smooth cut but with moving slowly the line will be quite steady. This is an amazing piece of technology and useful for a lot of other projects.
Step 6: Cut the Bird Hole
I used a 1 1/2" bit to cut this--the literature varies on this dimension and I wont get into it. The hole should be cut about half way up the side in the portion which curves the least--you don't want to press your luck when you are bending this stuff--holes definitely weaken it. Only one of the side pieces gets a hole!
Step 7: Assembly
The fun part. This takes a little goofing with but with a bit of gentle bending you can get all the pieces together. Get the top or bottom on first and then move it down on the pieces to stabilize it before putting on the opposite one. After getting it roughly together carefully adjust the top and bottom to match the wing shaped curves of the sides.
Step 8: Sealing It Up
Measure the openings on the two ends and cut side pieces to fit in these spaces out of the poplar plywood. The structure can be temporarily tacked together with a few dots of hot glue. The side and the top are self-tensioning and usually don't require this--only the end pieces.
Step 9: Epoxy Coating
The West System is very nice. It usually includes the self measuring pumps attached to the hardener and the epoxy. If you haven't used epoxy systems before you should read up on safety rules that come with the stuff. It is really easy to use and it takes about six pumps of each one to make a large enough batch to coat the whole structure. You use a sponge brush to mix the two components and to apply it to the structure. Not only does it glue the whole thing together into a composite structure it also forms a weather barrier to keep it going for many summers to come. Make sure you treat the end cuts of all the plywood. The stuff hardens overnight and this is the slow stuff so you have at least 20 minutes to put it on. Make sure you get the stuff into the cracks to glue and seal them. Only one coat of epoxy is necessary to seal and glue the structure. Wear latex gloves for this step.
Step 10: Sealing and Sanding
There will be some openings in the structure once the epoxy dries. Seal these with some wood filler of the appropriate color. The structure can then be sanded to smooth out the small defects that occur when applying epoxy for the first or fortieth time. The final structure can then be left a natural color by applying a polyurethane finish or an appropriate outdoor paint.
Step 11: Ready for the Birds
You may want to modify the design to make one of the small end panels come off for cleaning between residents. You can also cut the square edges off with your rotary cutter tool. These structures are very fun to make and modeling them with cardboard can get you a neat lunchbox or a variety of other bendable composite creations.