榫卯Chinese Joinery
中文
Board & panel joints
穿带
chuāndài

Chuandai (穿带): The Batten That Keeps Tops Flat

Chuandai · Dovetailed batten

Turn an old Chinese table over and you will find one or more bars running across the underside of the top. They aren’t nailed or screwed. They are slid in.

Each is a chuandai, a sliding dovetail batten. It holds a thin panel flat for centuries while still letting it swell and shrink with the seasons.

Chinese
穿带 · chuāndài
Joins
Battens to the back of a panel, and into the frame
Found in
Tabletops, cabinet doors and sides; door boards in buildings
Signature parts
Dovetail housing · tapered batten · tenon ends
Works with
Longfeng board joints, mitred frames
Drag to rotate. Slide to take the joint apart, or press Assemble to watch it go together.

How it works

A dovetail across the grain

A dovetail-section housing (带口) is cut across the back of the panel, and the batten has a matching trapezoid tongue. Slid in, the batten can’t drop out, and it stops the boards from cupping.

Why it tapers

Both housing and batten are slightly wider at one end, which craftsmen call 出梢. Driven in from the wide end, the batten tightens as it goes. Wang Shixiang warns that too much taper lets the batten creep back, and too little lets it slide straight through.

Into the frame

The ends of the batten are left long as tenons and go into mortises in the long sides of the frame, so the panel is held in the frame too.

How it's made

  1. Cut the housing
    Step 1

    Cut the housing

    Cut a dovetail housing across the back of the panel, slightly wider at one end.

  2. Shape the batten
    Step 2

    Shape the batten

    Plane the batten to a matching trapezoid tongue, tapered the same way.

  3. Leave tenon ends
    Step 3

    Leave tenon ends

    Leave the ends of the batten long as tenons.

  4. Drive it in
    Step 4

    Drive it in

    Slide the batten in from the wide end until it is tight.

    Tip Too much taper and it creeps back; too little and it slides through.

  5. Into the frame
    Step 5

    Into the frame

    The tenon ends go into mortises in the long sides of the frame.

  6. Check
    Step 6

    Check

    The panel lies flat but isn’t glued across its width.

Variations

How many battens

Wang suggests the outer battens about 15 cm from each end of the panel and roughly one every 40 cm between.

Hard and soft battens in buildings

Builders distinguish battens that stand proud of a door board from ones planed flush, and drive tapered battens from opposite sides.

Can you CNC this?

Possible, with design or setup changes

A tapered sliding dovetail can be cut with a dovetail bit: the groove across the panel is cut from the face and the taper is a change in width in plan, which a 3-axis machine handles. The batten’s dovetail edges may need the part on its side or the same dovetail bit from above. The fit is usually tuned by trial.

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).

Questions

What is a chuandai?

A tapered dovetail batten slid across the back of a Chinese panel to keep it flat; its ends tenon into the frame.

Why is it tapered?

So it tightens as it is driven in. Wang Shixiang notes the taper must be just right: too much and it backs out, too little and it slides through.

Is it glued?

The batten works by its dovetail fit, so the panel can still move with the seasons.

Further reading
  1. Wang Shixiang, 家具结构之结合: 基本接合 (excerpt), 中国文物网
  2. 文化知识 (excerpts from Wang Shixiang, 明式家具珍赏), 北京中国紫檀博物馆
  3. 边框与板结构, chinese-furniture.com
  4. 传统大木结构中的榫卯, 汉匠
  5. Ganeshan et al., MiGumi: Making Tightly Coupled Integral Joints Millable (SIGGRAPH Asia 2025)
  6. Jochen Gros & Friedrich Sulzer (HfG Offenbach), 50 Digital Wood Joints