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Plywood Scarfing

Because the Scaup is longer than eight feet I needed oversized plywood. Oversized plywood is created by scarfing several sheets together. Interestingly, the scarf joint itself is stronger than the plywood so no strength is lost. Originally I planned to buy plywood panels that had already been scarfed. This didn't happen because there are very few plywood suppliers that will scarf for you and those that do don't have the best prices. Therefore I decided to do it myself. The recommended scarf joint has a pitch of 1/8, meaning one inch of rise for every eight inches of run.

In order to create the necessary pitch on the end of the plywood I purchased a scarfing attachment for my circular saw. This attachment, developed and sold by the Gougeon Brothers (WEST Systems) bolts to the bottom of circular saws and will create a scarf joint in plywood up to 3/8" thick.

Below is a picture of all four panels stacked on top of each other after being cut with the scarfing attachment and sanded with a belt sander. Note the top two sheets which are BS 1088 plywood have seven plys while the bottom two sheets which are BS 6566 have five plys.

Epoxying the panels proved to be a little tricky. The first step was to put a coat of epoxy on the joint surfaces and let it soak into the end grain. This extra epoxy keeps the joint from soaking up all the epoxy and leading to a weak joint. The next step was to position two panels on the floor and tape them into place so that they would not shift. I put plastic underneath the joint to keep excess epoxy from gluing to the floor. I placed a straight edge between the two panels so that everything would be square. Next I mixed up more epoxy, this time adding wood flour until it reached the consistency of ketchup. I painted the joints and then put the remaining two sheets in place. I put plastic on the top of the joints and then placed books on top to apply mild pressure. Aftere the epoxy set up I had two 18' panels that were almost perfectly square. This gave me a real feeling of accomplishment.