3D model: Yatoi-hozo-shachi-sen-shiguchi by thejoinery on Sketchfab
Assembly insights
Shachi Sen introduces students to the concept of removing material to create interlocking connections. The joint's simplicity makes it perfect for learning saw control and chisel work, while its strength makes it practical for many applications. The name refers to the spline or key (sen) inserted into the lap, though beginner versions often omit the key.
Historical context
Shachi Sen (差し栓, inserted key) is a fundamental lap joint used in frame corners, shelf supports, and garden structures. It teaches the same half-lap principles as Mechigai Tsugi but at a simpler scale—two members meet at right angles with half the material removed from each. The optional spline adds shear resistance and prevents the lap from sliding apart under load.
Construction steps
- Mark half-lap depths on both members at the intersection using a marking gauge.
- Saw the lap faces on each piece, staying to the waste side of the line.
- Chisel the waste material flat; check that both halves seat flush at the corner.
- Optional: cut a slot across the lap and insert a wooden spline (sen) for extra strength.
- Test-fit the assembly; the corner should be square and rigid.
Where to see this joint in Japan
- Garden structures and pergolas — Temple gardens and private estates
- Interior shelf and frame construction — Traditional and contemporary woodworking projects
Variations
Keyed versions use a visible or hidden spline; unkeyed versions rely on friction and pegs. Lap depth can be one-third rather than half for lighter work. Related joints include Mechigai Tsugi (interlocking cross-lap) and Shachi-sen corner splines in fine cabinetry.
Applications
- Frame corners
- Shelf supports
- Garden structures
Tools required
- Dozuki saw
- Chisels
- Marking gauge
- Square