Shizi Chajie Sun (十字插接榫): Cross Insert Tenon
Cross insert tenon · 插接榫
Some Chinese columns are built from an upper and a lower length, divided at a bracket block or wrapped inside a casing.
The two lengths plug together with a cross-shaped insert tenon.
- Chinese
- 十字插接榫 · shízì chājiē sǔn
- Also called
- 插接榫
- Joins
- Upper and lower column lengths
- Found in
- Columns split at a block; cores of cased columns
- Variant
- Four-petal insert splice (四瓣插接榫)
How it works
Two lengths
A building-conservation guide describes insert splices as joining upper and lower columns divided by a block, and also the cores of cased columns.
A cross-shaped tenon
One end has a tenon shaped like a cross; the other has a matching cross-shaped mortise. The cross keeps the lengths from twisting or shifting.
Hoops
Iron hoops can be fitted at the joint. The guide gives the four-petal variant a length of about twice the column diameter; the cross tenon in the model is drawn shorter and its proportions are illustrative.
How it's made
Step 1Two lengths
A column in two lengths.
Step 2Cross tenon
A cross-shaped tenon on one end.
Step 3Cross mortise
A matching mortise in the other.
Step 4Plug together
Insert them end to end.
Step 5No twisting
They cannot twist or shift.
Step 6Hoops
Iron hoops at the joint (not shown).
Variations
Four-petal insert splice
A variant about twice the column diameter long.
Can you CNC this?
Possible, with design or setup changes
Both the cross tenon and the cross mortise are on end grain, so each length needs clamping upright. The mortise’s inside corners come out rounded; round the tenon’s corners to match.
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 column length 下段柱 · chajie-sun-column-lower.stl
- Upper length with cross tenon 带十字榫的上段柱 · chajie-sun-column-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
Hidden Dowel
àn xiāoTwo lengths meet end to end and a square pin hidden inside the joint keeps them in line: nothing shows outside.
Palm Splice
bāzhang sǔnOld column and new foot are each cut to a half-thickness “palm”; the palms overlap, short tenons lock their ends, and iron hoops bind it.
Through-Base Tenon
tàodǐng sǔnA long square tenon at the column foot passes through a hole in the base stone into the foundation below.
Questions
What is a cross insert splice?
A cross-shaped tenon joining two column lengths end to end.
Why a cross?
It stops the lengths twisting and shifting.
Is it reinforced?
Iron hoops can be fitted at the joint.