Step 1: Place one of the sides in front of you with the dado facing down and running
along the edge closest to you. Use this same orientation when performing
all the operations necessary to lay out the finger joints.
Step 2: Using a pencil, mark across the left side 1/2" in from the
edge
(against the grain).
Step 3: On this line, place a mark 1" in from both the top and bottom
of the side. Do the same at the very edge of the side.
Step 4: Connect your marks between the line and the edge of the side. You
should have two horizontal lines (with the grain) running between the pencil line and the
end
of the side.
Step 5: Cut out the two outer boxes formed by these lines. This will leave
you with a 3/4" wide by 1/2" deep tongue in the center of the
side's edge. Use this as a template for the left edge of each of the sides.
Mark and cut them all exactly the same.
Step 6: Next, place two of the sides in front of you, edge to edge. Then,
overlap the cut edge of the piece on the right over the square edge of
the piece on the left. Mark the area in the center of the edge which must
be cut out to receive the tongue.
Step 7: Cut out this area and test fit the two pieces. Make any adjustments
necessary so the joint looks like the illustration. Do this with all the
side pieces until they fit together to form a square, finger jointed frame.