The Japanese through tenon in this photo has a special feature that improves the performance of the joint in a timber frame.
In a typical Western style through tenon, the wood of the tenon itself provides the strength of the joint. However, in this Japanese tenon, a wider “stub” section fits into a housing on the connecting post.
The larger section of wood between the main beam and the tenon increases the strength of the joint. It also adds stability by reducing the amount of twisting in the beam.
Tim took this photo during a Japanese timber framing course taught by Dale Brotherton and Robert Laporte. For more information, visit their websites at www.japanesecarpentry.com and www.econest.com