Bladed scarf joint

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?

Reviewing Jack Sobon’s article on bladed scarf joints he writes: “The barefaced tenons prevent twisting and improve bending and tensile strength. Some builders added extra pins in the central lapped portion. Overall length is commonly four times the depth of the timber. Variations of this scarf may present sub tenons without pins or a shortened lapped portions. In one variation, the topmost and bottommost cuts are aligned vertically and the tenons lengthened. (See Cummings. fig 86 and Hewitt. fig 271) Tenons are typically 1 1/2 in. or 2 in. thick, and 4 in. or 6 in. long. Good luck, Jim

[This message has been edited by J Rogers (edited 08-21-2001).]

[This message has been edited by J Rogers (edited 08-21-2001).]