Gutou Sun (箍头榫): Beams Clasping Corner Columns
Gutou sun · Clasping tenon
At the corners of a Chinese building, the tie beams don’t stop at the column. They run straight past it and end in a carved head.
That head is doing a job. The gutou sun, the clasping-head tenon, locks the beam to the column so it can’t be pulled away.
- Chinese
- 箍头榫 · gūtóu sǔn
- Joins
- Tie beam to end or corner column
- Found in
- End bays and corners of timber buildings, pavilions
- Proportions
- Tenon 8/10 of beam height, 1/4–3/10 of column diameter wide
- Head
- 霸王拳 (large style) or 三岔头 (small style)
How it works
Slot in the column head
A slot is cut across the top of the column. On a corner column where beams arrive from two sides, slots are cut both ways.
Narrow tenon, wide head
The beam end is cut to a tenon about 8/10 of the beam’s height and no wider than 1/4–3/10 of the column diameter. It drops into the slot from above, and the beam continues past the column as a head about 8/10 of the beam’s size.
How far it runs past
Measured from the column centre, the head runs one column diameter with a 霸王拳 (“overlord’s fist”) end, used on large-style buildings with bracket sets, or 1.25 diameters with a 三岔头 end on small-style ones. Where two beams cross at a corner they are halved over each other, the side beam over the front.
How it's made
Step 1Slot the column
Cut a slot across the column head.
Step 2Cut the tenon
Narrow the beam end to a tenon that fits the slot.
Step 3Leave the head
Let the beam run past the column as a head.
Step 4Drop it in
Drop the beam into the slot from above.
Step 5Clasp
The head clasps the column.
Step 6Locked
The beam can’t be pulled away.
Variations
One-sided
On an end column, the slot runs one way.
Crossing at a corner
Two beams cross in a cross-slot, halved over each other.
Head forms
霸王拳 on large-style buildings, 三岔头 on small-style ones.
Can you CNC this?
Yes, with small changes
The slot across the column head opens at the end, so it can be cut from the side with the column lying down. Its inside corners will be rounded; round the beam’s matching edges or add reliefs.
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-Head Tenon
mántou sǔnA short square tenon on the column head fits a socket under the beam, so the beam can’t slide off.
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.
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.
Questions
What is a gutou tenon?
The joint where a tie beam drops into a slot in an end or corner column and runs past it in a head that clasps the column.
How far does the head project?
One column diameter from the column centre for a 霸王拳 head, 1.25 for a 三岔头.
Why let the beam run past?
The head locks the beam to the column.