Gejiao Sun (格角榫): The Mitred Frame Corner of Chinese Tabletops
Mitred mortise-and-tenon · 攒边格角
Nearly every Chinese tabletop, door and cabinet side is a frame with a thin panel floating inside. Look at a corner of that frame and you see only a single diagonal line.
That line is the mitred frame joint, 格角榫. It hides end grain on every face, locks the corner square, and gives the panel a groove to sit in.
- Chinese
- 格角榫 · géjiǎo sǔn
- Joins
- Long side (大边) to end (抹头)
- Found in
- Tabletops, chair seats, door and cabinet panels
- Signature parts
- 45° mitre · tenon on the long side · small triangular tongue
- Goes with
- Frame-and-panel (攒边打槽装板)
How it works
Long sides and ends
The two long members of the frame are the 大边; they carry the tenons. The two short ones are the 抹头; they take the mortises, often cut right through.
Two mitres and a tongue
Where they meet, both members are cut at 45°, so the corner shows only a diagonal seam. Beside the main tenon a small triangular tongue is left at the mitre. It can be hidden (闷) or allowed to show (明).
Why a frame at all
The frame’s inner edge is grooved, and a thin panel with a tongue all round sits in the groove. Battens slide across the underside and tenon into the long sides. Thin boards then do the work of a thick slab, the ugly end grain disappears, and the panel can still move with the seasons.
How it's made
Step 1Cut the mitres
Mark and cut 45° mitres at the ends of the long side and the end.
Step 2Cut the tenon
Leave a tenon on the long side, projecting beyond the mitre.
Step 3Cut the mortise
Cut the matching mortise in the end, usually right through.
Step 4Leave the small tongue
Form the small triangular tongue at the mitre, hidden or showing.
Step 5Push the end on
Slide the end onto the tenon until the mitres close.
Step 6Groove for the panel
Cut a groove round the inner edge to take the panel’s tongue.
Variations
Hidden tongue
The triangular tongue stays inside the joint and doesn’t show.
Showing tongue
The tongue comes through to the surface as a small triangle.
Woven seats
On chairs and beds with woven rattan seats, the frame is mitred the same way and drilled for the weave.
In museum collections
Minneapolis Institute of Art
Minneapolis Institute of Art
Related joints
Long-and-Short Tenons (长短榫)
Two tenons at right angles on the top of a leg: a long one for the long side, a short one for the end.
Zongjiao Joint (粽角榫)
Three members, three 45° mitres, one perfect point: the corner joint of flush-sided tables and cabinets.
Dovetail Joint (燕尾榫)
A tenon wider at the tip than at the root, so it can’t pull out: found in boxes, drawers, tables and temple beams.
Questions
What is a gejiao joint?
The mitred mortise-and-tenon corner of a Chinese frame: the long side carries a tenon into the end, both are cut at 45°, and a small triangular tongue sits at the mitre.
Why mitre the corner?
A mitre hides the end grain on both visible faces and lets mouldings run round the corner unbroken.
Why is there a groove?
The frame holds a floating panel. Its tongue sits in the groove, so the panel can expand and shrink without cracking.