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中文
Loose tenons, pins and wedges
穿销
chuān xiāo

Chuan Xiao (穿销): the Sliding Key That Holds a Long Apron

Sliding key · 穿销

By · Updated

A long, thin apron on a bench or bed can work loose and bow.

A sliding key through its back at mid-span holds it to the frame.

Chinese
穿销 · chuān xiāo
Joins
Long apron to the frame above
Found in
Benches, long tables, beds
Signature parts
Half-dovetail key · groove in the apron back · top tenon
Compare
Loose tenon
Drag to rotate. Slide to take the joint apart, or press Assemble to watch it go together.

How it works

Unlike a loose tenon

A loose tenon (栽榫) is short and hidden. Wang Shixiang distinguishes the sliding key: it is longer, shows on the back of the part, and is out of sight in use.

Where and how

On some benches, long tables and beds a groove is cut in the back of the apron at mid-span, and a long key with a half-dovetail section slides through it like a batten. Its top end is a tenon into a mortise in the underside of the frame, so the apron is held tight.

Only when needed

He adds that the best makers used loose tenons and keys only when they had to: an apron cut thick enough does not need one. In timber buildings, keys passing through several layers are also used, for example in the tails of some bracket sets.

Proportions in the model are illustrative.

How it's made

  1. Problem
    Step 1

    Problem

    A long apron can bow away.

  2. Groove
    Step 2

    Groove

    A groove in the back at mid-span.

  3. Key
    Step 3

    Key

    A long key, half-dovetail section.

  4. Tenon
    Step 4

    Tenon

    Its top end is a tenon.

  5. Slide
    Step 5

    Slide

    Slid through like a batten.

  6. Held
    Step 6

    Held

    The apron is held tight to the frame.

Variations

In buildings

In timber frames a key may pass through several layers and be wedged.

Can you CNC this?

Possible, with design or setup changes

The half-dovetail groove can be cut with a dovetail bit along the back of the apron, and the key with the same bit. The key’s top tenon needs a second setup.

Free STL downloads (one file per part)

Before cutting or printing, read the CNC and 3D-printing notes on tool radius, scaling the STL files and their licence.

Questions

How is it different from a loose tenon?

It is longer and shows on the back.

Why half-dovetail?

So the apron cannot pull off the key.

Is it always needed?

No, a thick apron does without.

Further reading
  1. 王世襄《明式家具研究》（Wang Shixiang, Research on Ming Furniture），第 119 页，图 3.45
  2. 马炳坚《中国古建筑木作营造技术》第二版（Ma Bingjian, Timber Construction Techniques of Traditional Chinese Buildings, 2nd ed.），第 126 页，图 3-11、3-12