Piao Jian (飘肩): The Toad-Shoulder Joint

Toad shoulder · 蛤蟆肩

Where a round stretcher meets a round chair leg and their outer faces line up, the joint can’t have an ordinary shoulder.

Beijing makers called the solution piao jian, the flying shoulder, or the toad shoulder, because it looks like a toad’s open mouth.

Chinese: 飘肩 · piāo jiān
Also called: 蛤蟆肩 (toad shoulder)
Joins: Round stretcher to round leg, flush outside
Found in: Base stretchers of round-back armchairs and other round-leg pieces
Compare: Mitred shoulder for square stock

Drag to rotate. Slide to take the joint apart, or press Assemble to watch it go together.

How it works

Flush outside

When the stretcher’s outer face lines up with the leg’s outer face (交圈), as with a round-back armchair’s base stretchers, Wang Shixiang explains that the tenon is left on the inner half of the stretcher end and the outer half is cut as a shoulder.

It floats

That leaves a large gap under the shoulder where it wraps the curve of the leg, so it seems to float. Hence “flying shoulder”, or “toad shoulder” for its open-mouth look.

When it isn’t flush

If the stretcher is set back from the leg’s face, both sides get shoulders and the tenon sits in the middle of the crescent-shaped end.

How it's made

Step 1
Flush faces
The stretcher’s outer face lines up with the leg.
Step 2
Inner-half tenon
Leave the tenon on the inner half.
Step 3
Outer shoulder
Cut the outer half as a shoulder.
Step 4
Mortise the leg
Mortise the round leg.
Step 5
It floats
A large gap opens under the shoulder.
Step 6
Toad shoulder
Its other name, for the open-mouth look.

Variations

Not flush

Shoulders on both sides and the tenon centred when the leg is thicker and the stretcher is set back, sitting in a crescent-shaped hollow.

Same thickness

When stretcher and leg are equally thick, shoulders on both faces and the tenon in the middle.

Can you CNC this?

Hard on a 3-axis machine as drawn

Hard: the shoulder of the round stretcher has to wrap the round leg, which is a curved, coped surface. It may need a 4th axis or 3D ball-nose surfacing, and the fit would likely need hand finishing.

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)

Leg 腿足 · piao-jian-leg.stl
Stretcher 枨子 · piao-jian-stretcher.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).