I learned to make scarf joints in boatbuilding school—simple nibbed joints that relied on glue and metal fasteners—not the complex all-wood joints used by traditional Japanese carpenters. And those traditional joints were stronger and more permanent than mine.

There were good reasons for the development of interlocking joinery: Japanese structures required longer beams than could be cut from the available trees and mankind had yet to invent glulams, LSLs, and other engineered lumber. Traditional joinery is no longer required but it is still used on some projects in Japan.

In the video below you can see a Japanese carpenter lay out and then cut an interlocking scarf. He roughs the pieces out with a portable electric mortising machine; the rest of the work is done with traditional hand tools. Most amazing of all is how the pieces lock together when he drives a strategically placed wooden wedge. Remove that wedge and the joint could be disassembled.