Refer this article for more on end to end joints : http://www.woodmagazine.com/woodworking-tips/techniques/joinery/end-to-end
The techniques shown in the above link rely mainly on having a table saw and is meant for smaller work pieces. Now, if you do not own a table saw or that the pieces are really long, say 8 feet long and you want to create a piece that is say 14 feet long, it is not practical to use a table saw. The same joint can be accurately created using a router.
First off, measure and mark 1/4" + the width of your work piece on both the pieces by placing them next to each other and marking them simultaneously.
Fit a 16mm slot cutting bit in the router. Measure the offset from the end of the slot cutting bit to the guide on the router bottom plate. Mark the offset on the wood.
|Note the "router offset"|
Fix a fence on the router offset, so that the router does not cut beyond the joint.
|Fence fixed on the router offset|
Adjust the depth of the router to 1/3rd the thickness of the work piece. For a 1.5" board, adjust the depth to 1/2". You can use a 1/2" ply as a reference.
Starting at the end of the board, run the router throughout the area that has to be removed.
Sand the surface after routing to get a more even surface for the glue to adhere.
To create the dado, mark half the width of the work piece on the newly formed lap. Set the router depth to 2/3rd the thickness of the work piece. Now for the tricky part, the router does not have a level surface to sit on, the lap is lower than the work piece thickness. So, we use the 1/2" ply that we used to gauge the depth of the router bit to create a level surface and then run the router. This will create the tabled lap on one of the work pieces, repeat the same on the other piece.
Now, align the joint and trim the excess wood we left on originally. Generously apply wood glue on the surface of the lap and strongly secure the the joint.
You can buy the tools used in this tutorial @ http://www.paintnhardware.com/27-tools