Perry has a great post on this
here, but unfortunately the photos have disappeared, so here is my take, hopefully with working photos...
Materials needed:
1x6 6ft long.
1x8 at least 15-1/4 inch long
Table saw
Glue
nails or screws
Cut the 1x6 into 4 pieces, 1 @ 22", 3 @ 15-1/4" on a 6 ft board there will be very little waste.
cut the 1x8 to 15-1/4 length. set aside with other 1x6 of same length.
Rip the 22" piece into 2 pieces that are 1-7/8" wide. The extra piece can be cut to 14-3/4 length and ripped down to 3/4". This will be the back part of the bottom board.
Next dado a groove 3/4" wide 3/4 from the top (3/8" from the bottom) on each of the 22" pieces.
This is where the 15-1/4" pieces will go, so it would be a good idea to dry fit them to make sure the dado is wide enough.
Next, rabbit the long edges of the 15-1/4" stock - 2 pieces will have to be done on both sides. Make sure the rabbits are exactly 1/2 the width of the board so when they fit together, both ends are flush.
3/8" should be 1/2 way - you may want to test this depth on the scrap left over from the 1x6 to make sure you have it right...
once the rabbits have been cut, you are ready for assembly! lay out your pieces in the order you want them, then glue the groves and slide each 15-1/4 board into the 22" pieces.
Nail or screw the bottom boards to the 22" pieces to keep them in place. Attach the now 14-3/4"x3/4" to an end to complete the assembly.
