Shizi Cheng (十字枨): The Cross-Halving Joint
Cross halving · 十字卡腰 · 马蜂腰
When two pieces of wood have to cross in the same plane, neither can pass straight through the other.
Each gives up half instead. In furniture this is the shizi cheng (cross stretcher); in buildings, the shizi kayao, cross waist joint.
- Chinese
- 十字枨 · shízì chéng; 十字卡腰榫
- Also called
- 马蜂腰 (wasp waist) in building carpentry
- Joins
- Two members crossing in one plane
- Found in
- Crossed stretchers, lattices, crossing purlins and plates
- Related
- Wrapped stretchers
How it works
Half and half
One member is cut away by half its depth on top, the other by half on the bottom. Dropped together they cross flush and lock against sliding both ways.
In buildings
Crossing purlins at a corner and crossing plates use the same cross waist joint. Building manuals add a rule: the side member is laid over the front one (山面压檐面).
How it's made
Step 1Halve the lower
Cut half the depth from the top of one.
Step 2Halve the upper
Cut half from the bottom of the other.
Step 3Drop together
Drop one into the other.
Step 4Locked
The notches stop sliding both ways.
Step 5Flush
The faces are flush.
Step 6Where
Stretchers, lattices, purlins.
Variations
Purlins at corners
Crossing purlins with the ends running past.
Can you CNC this?
Yes, with small changes
A cross halving is two notches cut straight down. The notch corners will be rounded, so add dogbone reliefs or round the mating edges.
General note: a round cutter cannot leave a sharp inside corner, so every recess keeps the tool radius. Round the mating edges or add dogbone reliefs. Sloping faces, undercuts and curves may need special bits, extra setups or more axes.
Free STL downloads (one file per part)
- Lower member 下方构件 · shizi-cheng-member-lower.stl
- Upper member 上方构件 · shizi-cheng-member-upper.stl
Proportions are illustrative, not measured dimensions. The files are unitless: scale them to suit and check fits and allowances before cutting. Each file is a closed (watertight) solid with its mortises and slots already cut, exported in its assembled position, ready to import into CAM or modelling software. Licence: CC BY 4.0 (credit: Chinese Joinery).
Related joints
Questions
What is a cross-halving joint?
Two crossing members each notched half their depth so they fit flush.
Where is it used?
Crossed stretchers, lattices and crossing purlins.
Which goes on top in buildings?
The side member over the front one.