This jig requires one peice of hardwood 3/4" square X 5 1/2" inches long and one peice 3/4" X 2 1/2" X 5 1/2" long. Mark off the 5 1/2" long peice as shown below, clamp it to the 3/4" X 2 1/2" peice, 1 1/2" from the top edge and drill the four 1/4" holes. It would be best to use a drill press for this if possible as the holes should be square.
Fasten the 3/4" square peice to the 3/4" X 2 1/2" with two screws as shown above making sure it is even at the top.
To Use Jig
This jig will work for 2 1/2", 3 1/2" and 5 1/2" wide boards, as the holes are spaced so that two holes will be 3/4" from the edge of each size.
Put jig over end of board, clamp and drill two 1/4" holes.
Lay second board on top of first board line up ends and edges and clamp together, place jig on end as shown and put a 1/4" pin through the hole of the jig into one of the holes drilled in first board, ( I have a Craftsman #2 phillips screwdriver that is the perfect size for this.)
Drill two 1/4" holes into side of second board using a stop on the drill bit so it will not go all the way through the board.
This jig can also be used to fasten boards together lenghtwise, drill holes spaced along the edge of the first board, then with second board clamped to first board and a pin through the holes drill the approprate holes in the face of second board.