Mantou Sun (馒头榫): The Column-Head Tenon
Mantou sun · Bun tenon
In a Chinese timber building, a heavy beam sits directly on top of each column. What stops it from sliding?
A small block on the column head, named after a steamed bun: the mantou sun.
- Chinese
- 馒头榫 · mántou sǔn
- Joins
- Column head (or king post) to beam
- Found in
- Timber-frame halls, pavilions, houses
- Size
- About 1/4–3/10 of the column diameter, slightly tapered
How it works
A short square tenon
The top of the column (or a king post) is cut to a short square tenon, its length, width and thickness about a quarter to three-tenths of the column diameter, slightly tapered with the top edges eased.
Into the beam
It goes into a socket (海眼) cut in the underside of the beam. The beam’s weight holds it down; the tenon stops it sliding sideways.
How it's made
Step 1Cut the tenon
Cut a short square tenon on the column head.
Step 2Size
About 1/4–3/10 of the column diameter.
Step 3Socket the beam
Cut a socket in the underside of the beam.
Step 4Lower the beam
Lower the beam onto the column.
Step 5Located
The tenon stops the beam sliding.
Step 6Hidden
Once in place it can’t be seen.
Variations
On king posts
The same tenon tops king posts (瓜柱) under ridge beams.
Can you CNC this?
Yes, with small changes
A short square tenon and a socket under the beam: both are cut straight from one direction. Round the tenon corners to match the socket, or add dogbones.
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)
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
Column-Foot Tenon
guǎnjiǎo sǔnA short round tenon at the column foot drops into a socket in the stone base, so the column can’t shift.
Clasping-Head Tenon
gūtóu sǔnThe beam drops into a slot across the column head and runs on past it; the head beyond “clasps” the column.
Big-In, Small-Out Tenon
dàjìn xiǎochū sǔnPart blind, part through: a big tenon enters, a small one shows. It lets two stretchers share a leg without weakening it.
Questions
What is a mantou tenon?
A short square tenon on a column head fitting a socket under the beam.
How big is it?
Traditionally about 1/4–3/10 of the column diameter.
Why the name?
Its short, rounded-off block shape is likened to a steamed bun.