Liangzhu Gumao (梁柱鼓卯): The Song Dovetail That Drops a Beam into a Column

The drawing

In juan 30 of the Yingzao Fashi (1103), the plate of mortises for beams and lintels (梁額等卯口第六) opens with two beam-to-column joints. In both, the beam end ends in a small projecting head and the column top has a long slot cut down from its upper end. In the 梁柱鼓卯 the head is a plain dovetail; in the 梁柱鉸口鼓卯 the beam shoulder is also notched (鉸口) where it meets the round column.

How it works

鼓卯 means a tenon that swells at the end, like the iron cramps the same book uses to tie stone blocks. The beam is lowered so its head slides down the slot; once in, the wide head cannot pass the narrow mouth, so the beam cannot pull away from the column. The weight above keeps it from lifting.

Inferred reconstruction (推断复原)

This joint is an inferred reconstruction. It is inferred from: the two juan 30 drawings of 梁柱鼓卯 and 梁柱鉸口鼓卯. Inferred, not sourced: the neck and head widths, the depth of the dovetail below the column top, and the beam and column sizes; the drawing gives no measurements, and the shoulder notch of the 鉸口 version is not modelled.

The drawing

In juan 30 of the Yingzao Fashi (1103), the plate of mortises for beams and lintels (梁額等卯口第六) opens with two beam-to-column joints. In both, the beam end ends in a small projecting head and the column top has a long slot cut down from its upper end. In the 梁柱鼓卯 the head is a plain dovetail; in the 梁柱鉸口鼓卯 the beam shoulder is also notched (鉸口) where it meets the round column. (Yingzao Fashi juan 三十 (plate scan p. 29)).

鼓卯 means a tenon that swells at the end, like the iron cramps the same book uses to tie stone blocks. The beam is lowered so its head slides down the slot; once in, the wide head cannot pass the narrow mouth, so the beam cannot pull away from the column. The weight above keeps it from lifting.

Inferred reconstruction (推断复原). This joint is an inferred reconstruction. It is inferred from: the two juan 30 drawings of 梁柱鼓卯 and 梁柱鉸口鼓卯. Inferred, not sourced: the neck and head widths, the depth of the dovetail below the column top, and the beam and column sizes; the drawing gives no measurements, and the shoulder notch of the 鉸口 version is not modelled.

Sized to the piece

The cited source shows the geometry of 梁柱鼓卯; it does not always publish one millimetre formula for every furniture or building size. Makers sized members to the span and stock in hand.

Proportions in the model are illustrative.

Common mistakes

• Driving the beam in from the side. The dovetail only enters down the open-topped slot; a sideways push cannot clear the narrow mouth.
• Treating neck, head, and slot depth as book figures. Juan 30 draws the shape; it gives no measurements. Sizes on this page are inferred.
• Reading it as the notched-shoulder (鉸口) version. That plate also shows 梁柱鉸口鼓卯 with a shoulder cut around the round column; this model is the plain dovetail only.
• Confusing it with opposed tenons. One beam dropping into a column top is 鼓卯; two beams lapped and pinned inside the column is liangzhu-duimao.

Related forms

Western and Japanese workshops have relatives that share a geometric idea (scarf, bridle, dovetail, halving, keyed splice) under other names; they are bridges for readers, not claims of descent.

Stay with the Chinese construction on this page before renaming a piece. See also Compare two joints when a look-alike is listed there.