I am planning on using a bladed scarf joint in a building that I am working on. I learned about it from the book Timber Frame Construction by Jack Sobon and Roger Schroeder. It is discussed on page 94. My question is how long should the joint be to connect two 8 x 8 white pine timbers. Also, how long should each "blade" be? I was planning on making the total scarf about 30 inches and each "blade" about 6 inches. Is this sufficient?