The Lu Ban Lock: Carpentry Without the Usefulness

Quick answer: the Lu Ban lock is six notched wooden sticks that interlock into a cross and hold together with no glue or fastening. It is also called the Kongming lock, it is one of China's four classic puzzles, and it is the direct ancestor of every burr puzzle made since.

Best for: anyone who wants to know where interlocking puzzles actually came from.

Most puzzles were designed to be puzzles. This one was a carpentry technique first, and became a puzzle when somebody removed the thing it was holding up.

What Is a Lu Ban Lock?

Six sticks, each notched so that it passes through the others, assembled into a symmetrical cross. Nothing fastens them. The pieces hold because of their shape, and taking the assembly apart requires finding the one piece that moves first.

That is also the definition of a burr, and the six-piece version sold in every gift shop is the same object. What differs is the history and, usually, the joinery: the traditional forms come from a mortise-and-tenon tradition rather than from puzzle design.

The family and its sub-types are set out in the guide to mechanical puzzles and in detail in the complete guide to interlocking puzzles.

Who Was Lu Ban?

A craftsman and structural engineer of the Spring and Autumn period, and the figure Chinese carpentry traditionally traces itself to.

The legend attached to the puzzle is that he made it to test his son. That is a legend rather than a record, and it should be read the same way as the turtle in the Lo Shu magic square story: a good tale explaining an object whose actual origin nobody wrote down.

What is not legend is the engineering. The interlocking mortise-and-tenon joinery the puzzle is built from is the same joinery that held up Chinese timber buildings, which is why the object feels so unlike a toy. It is a structural technique with the structure taken away.

Why Is It Also Called the Kongming Lock?

Because of a second attribution, several centuries later.

During the Three Kingdoms period, Zhuge Liang is said to have turned Lu Ban's device into something for soldiers to play with in idle hours. Kongming was his courtesy name, so the puzzle carries it.

Both names are in use and they describe the same object. The split tells you something about how puzzles acquire histories: one story credits the inventor of the technique, the other credits the person who made it an amusement, and both are probably part true.

What Are China's Four Classic Puzzles?

Worth knowing, because together they cover most of what mechanical puzzling is.

• Luban Lock - interlocking, this one.
• Nine Linked Rings - the Chinese rings, which is a binary counting machine in disguise.
• Huarong Dao - a sliding block puzzle, and the ancestor of the modern ones.
• Tangram - the seven-piece dissection.

Four objects, four completely different problems: interlocking, sequence, sliding and dissection. Any one of them would be a reasonable introduction to the field, and between them they anticipate most of the seven categories used to classify puzzles today.

How Many Pieces Can One Have?

Six is the classic, and the tradition goes a great deal further.

Larger Lu Ban locks exist in twelve, eighteen, twenty-four pieces and beyond, built on the same principle with more sticks crossing in more directions. They are sold as tests of patience, and they are more difficult in the bookkeeping sense rather than the insight sense: more pieces to keep oriented, not a cleverer idea.

This is the distinction that runs through the whole interlocking family and it is worth internalising before buying anything. Piece count measures how much there is to track. Difficulty lives in the move sequence, which is measured by level notation and explained in what makes a puzzle hard. A six-piece burr with a long solution beats an eighteen-piece one that comes apart in three moves.

How Do You Solve a Lu Ban Lock?

By finding the key piece, which is the same method as any six-piece burr.

Look for the piece with the fewest notches. In the classic six-stick form one piece is plain or nearly so. That is the key: it goes in last and it comes out first, and it is what locks the other five.

Work flat, not in the air. Build on a table and let gravity hold the partial assembly. Holding it in mid-air means fighting five loose pieces at once.

Note the orientation before you dismantle it. The notches are not symmetrical and the pieces are easy to confuse once they are in a pile.

There is a full walkthrough in how to solve the 6-piece burr, which is the same puzzle under its European name.

What Do We Make?

The modern descendants, in 3D-printed form rather than hardwood.

6-Piece Cross is the classic itself, and 3-Piece Cross is the gentler introduction. From there the family runs into the turning interlocking cubes, where pieces rotate rather than slide, covered in turning interlocking cubes.

The whole shelf is interlocking puzzles, and the wider range is mechanical puzzles.

Frequently Asked Questions

What is a Lu Ban lock?

Six notched wooden sticks that interlock into a cross and hold together by their shape alone, with no glue or fastenings. It is the Chinese ancestor of the burr puzzle and is built on the same mortise-and-tenon joinery used in traditional timber architecture.

Is the Lu Ban lock the same as a burr puzzle?

Effectively yes. The six-piece version is the same object as the six-piece burr sold in the West. The names differ by tradition rather than by mechanism.

Why is it called the Kongming lock?

Kongming was the courtesy name of Zhuge Liang, who is said to have adapted Lu Ban's device into a pastime for soldiers during the Three Kingdoms period. Both names refer to the same puzzle.

What are the four classic Chinese puzzles?

The Luban Lock, the Nine Linked Rings (Chinese rings), Huarong Dao (a sliding block puzzle) and the Tangram. Between them they cover interlocking, sequential, sliding and dissection problems.

How do you take apart a Lu Ban lock?

Find the key piece, which is the one with the fewest notches or none at all. It comes out first and locks the other five. Work on a table rather than in your hands, and note which way round the pieces sat before you dismantle it.