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Using a pencil, trace the lap on each piece of wood. The lap should be half the thickness of the wood and two to four times as long as the wood is thick. It's essential to measure so that the laps on both pieces of wood have identical dimensions.
Set a table-saw blade at exactly half the thickness of the first strip of wood. In this case, the pieces of wood are 2" x 4" lumber, whose thickness is actually 1-1/2", so the saw blade is set at a height of 3/4".
Pass the wood through the blade, starting at the innermost edge of the lap (Image 1). Make as many passes as needed, working the blade toward the end of the work piece. Eventually you'll create an L shape in the wood (Image 2).