Hezhu Gumao (合柱鼓卯): How Song Builders Made One Column from Two Pieces

The drawing

Juan 30 has a plate of its own, 合柱鼓卯第七. It draws a column made of two pieces (兩段合) and one of three (三段合), with small keys set along the seams at four heights. A cross-section (正樣) shows two bow-tie keys across the seam, hidden inside (暗鼓卯). Beside it are visible keys let into the surface and covered (蓋鞠明鼓卯), and small blocks.

The bow-tie

鼓卯 is a key wide at both ends and narrow in the middle. The same book lists iron ones for tying stone blocks: each end 2 cun wide and 1 cun long, the waist 4 cun long. A wooden key of this shape across the seam pulls the two pieces together.

Inferred reconstruction (推断复原)

This joint is an inferred reconstruction. It is inferred from: the 合柱鼓卯 plate in juan 30, its cross-section, and the iron 鼓卯 in juan 26. Inferred, not sourced: the size and proportions of the wooden keys (borrowed from the iron ones), their number and spacing, and how they are fitted; the three-piece version and the surface keys are not modelled.

The drawing

Juan 30 has a plate of its own, 合柱鼓卯第七. It draws a column made of two pieces (兩段合) and one of three (三段合), with small keys set along the seams at four heights. A cross-section (正樣) shows two bow-tie keys across the seam, hidden inside (暗鼓卯). Beside it are visible keys let into the surface and covered (蓋鞠明鼓卯), and small blocks. (Yingzao Fashi juan 三十 (plate scan p. 31)).

鼓卯 is a key wide at both ends and narrow in the middle. The same book lists iron ones for tying stone blocks: each end 2 cun wide and 1 cun long, the waist 4 cun long. A wooden key of this shape across the seam pulls the two pieces together.

Inferred reconstruction (推断复原). This joint is an inferred reconstruction. It is inferred from: the 合柱鼓卯 plate in juan 30, its cross-section, and the iron 鼓卯 in juan 26. Inferred, not sourced: the size and proportions of the wooden keys (borrowed from the iron ones), their number and spacing, and how they are fitted; the three-piece version and the surface keys are not modelled.

The bow-tie

鼓卯 is a key wide at both ends and narrow in the middle. The same book lists iron ones for tying stone blocks: each end 2 cun wide and 1 cun long, the waist 4 cun long. A wooden key of this shape across the seam pulls the two pieces together.

Proportions in the model are illustrative.

Common mistakes

• Leaving the bow-tie keys visible on the outside. This page models the hidden keys (暗鼓卯) inside the seam; surface keys (蓋鞠明鼓卯) are a different drawing on the same plate.
• Treating wooden key size and spacing as book figures for timber. Shape follows the iron 鼓卯 in juan 26 (ends 2 cun wide, waist 4 cun long); wooden sizes and spacing here are inferred.
• Reading a three-piece column as the same model. Juan 30 also draws 三段合; this reconstruction is the two-piece (兩段合) version only.
• Confusing it with a furniture butterfly key. Same bow-tie idea, different use: here the keys splice a built-up column. Compare yinding-sun.

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.