Tuesday, September 13, 2011

Plywood Scarf Joint

A couple of posts back I came up with a fixture that would help me make a scarf cut on the 4 foot length of the plywood sheet that provided a feature to strongly bond 3 sheets of plywood end to end.  I need a sheet of plywood 24 feet long to make the panels for the main hull and floats.

I clamped the sheet of plywood adjacent to the fixture and ran a circular saw along the edge to make the cut.  Once I had the scarf joint cut on all three sheets, I applied epoxy thickened with wood flour to the joint and aligned the sheets.  It is very important to make sure the long edge of the sheet is straight since this edge is used to layout the parts.  After the sheets were aligned, I placed a two by four on top of the joint and clamped the piece tightly to the work bench.  I also placed a sheet of plastic drop cloth between the workbench and the clamp board.

After the epoxy has cured for 24 hours, I removed the clamps and used a belt sander with a 120 grit belt to sand the joint smooth.  I sanded both sides. 

Once I had made two panels, I decided to use my two workbenches as a fixture by screwing stop boards to the long side of the bench and using a string to align both benches in a straight line.  Now I just push the 4 x 8 sheets up against the stops, align the scarf joint so the overlap is correctly position and then clamp the joint for curing.  Aligning the benches makes sure the panel is straight.  The process works great!

Next step...Lofting and cutting the panels.

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