Dajin Xiaochu (大进小出): The Half-Through Tenon

Dajin xiaochu · Half-through tenon

A through tenon is strong, but it chops a big hole through the leg. When two stretchers meet a cabinet leg at the same height, two such holes would leave the leg hollow.

The dajin xiaochu, “big in, small out”, solves it: each tenon is big where it enters and only a small part runs through.

Chinese: 大进小出 · dàjìn xiǎochū
Joins: Rails or beams to a post
Found in: Cabinet base stretchers; beams in timber buildings
Signature parts: Blind part · through part
Purpose: Lets two tenons pass each other

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How it works

Big in, small out

Part of the tenon is a blind tenon and stops inside; part is a through tenon and shows on the far face. The area entering the mortise is large, the area showing is small.

Two stretchers, one leg

Wang Shixiang’s example is a cabinet base, where front and side stretchers meet the leg at the same height. The side stretcher cuts away the lower half of its tenon and keeps the upper half through; the front one does the opposite. The tenons pass each other, the leg is not hollowed out, and both sides still get strong through tenons.

In buildings

Timber buildings use the same joint where tie beams enter columns.

How it's made

Step 1
Blind part
Cut the large part of the tenon to stop inside the post.
Step 2
Through part
Leave a smaller part that runs right through.
Step 3
The other stretcher
Make the second stretcher the other way round: lower half through.
Step 4
Fit both
Bring both stretchers to the post at the same height.
Step 5
Through ends
On the outside only small tenon ends show.
Step 6
Shared leg
The tenons pass each other and the post isn’t weakened in one spot.

Variations

Cabinet base stretchers

Both stretchers big-in-small-out, halved the opposite way.

Through and blind

Alternatively the front stretcher goes through and the side one stays blind, with the apron below the side stretcher tenoned through instead.

Can you CNC this?

Yes, with small changes

A stepped mortise, partly blind and partly through, is cut from the face of the leg; the through part may need finishing from the other face to keep the exit clean. Round the corners of the mortises or the tenons as usual.

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)

Post 竖材 · dajin-xiaochu-post.stl
Stretcher (front) 枨子（正面） · dajin-xiaochu-stretcher-front.stl
Stretcher (side) 枨子（侧面） · dajin-xiaochu-stretcher-side.stl

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).