The Altekruse: Twelve Identical Pieces

Quick answer: the Altekruse is a twelve-piece burr in which every piece is identical, each cut with three notches. It has no key piece. It opens by sliding two complete halves in opposite directions, and nothing can be removed until that happens. William Altekruse patented it in 1890.

Best for: people who already solve burrs and will therefore spend a long time looking for a key piece that is not there.

Almost every interlocking puzzle has one piece that moves first. This one has none, and that single difference is the whole puzzle.

What Is the Altekruse Puzzle?

Twelve pieces, all the same. Each is a square-section stick with three notches, where the two end notches face the same direction. Assembled they form a symmetrical cross, and it belongs squarely in the family described in burr puzzles explained.

Identical pieces are rarer than you might expect in this field. Most interlocking puzzles get their difficulty from pieces that differ subtly, so the work is partly in telling them apart. Here there is nothing to tell apart, and the puzzle is still hard.

Why Does It Have No Key Piece?

Because it does not come apart piece by piece. It comes apart in halves.

In an ordinary burr one piece is unnotched or less notched than the rest, and removing it frees everything else. That is the key, and finding it is most of the solve, which is why the level notation counts moves to free the first piece.

The Altekruse does something else entirely. Two complete sections slide against one another in opposition, and only once they have separated can an individual piece be taken out. Nothing you press or pull on a single stick will achieve anything, because no single stick is free to move.

Depending on how it has been assembled, that sliding action can happen along one axis, two, or all three independently, though never more than one at a time. So the first real question is not which piece moves, but which way the whole thing splits.

Who Was William Altekruse?

An Austrian who left to avoid being conscripted, and whose surname is a small joke the puzzle world has enjoyed ever since.

Altekruse means old cross in German. The family was Austrian-German, and William came to the United States in 1844 with three brothers, leaving to escape the draft.

He was granted his patent in 1890 for a symmetrical twelve-piece burr that assembles into a cross. A man called old cross patented the cross puzzle, which is the kind of coincidence nobody would dare invent.

Can It Be Built With Other Piece Counts?

Yes, and the person who worked that out is one we write about.

Stewart Coffin found that the same piece can be assembled not only as twelve but also as fourteen. Larger versions of thirty-six or thirty-eight pieces are possible too.

That is an unusual property. Most interlocking puzzles are a fixed object: a six-piece burr takes six pieces and no other number. Here the piece is a component rather than a part, and the assembly is a family of shapes instead of one shape, which is much closer to how Coffin thought about design generally.

How Do You Solve It?

Stop hunting for a loose piece. There is not one. Pressing each stick in turn, the correct method for most burrs, will tell you nothing here and is where most experienced solvers lose their first half hour.

Push on a whole face, not a piece. Place a palm on one side of the assembly and press the opposite side the other way. You are testing whether the solid splits along that axis.

Try all three axes. Only one will usually give, and which one depends on how it was put together. If none does, the halves are not aligned to separate and something needs seating properly first.

Reassembly is the harder half. Twelve identical pieces means orientation is everything and there is no landmark to work back from. Photograph it assembled before you start, which is advice worth taking more seriously here than almost anywhere else.

Why Are Identical Pieces So Rare?

Because they make a designer's job much harder, not easier.

If every piece may differ, a designer has an enormous vocabulary: notch one stick here, another there, and the assembly can be forced into almost any sequence they like. Most burrs are designed that way, and the published level is the measure of how cleverly it was done.

Insisting that all twelve pieces be the same removes nearly all of that freedom. The single piece must work in twelve different roles and orientations at once, and whatever notch you cut to solve one position is simultaneously cut into the eleven others. Most attempts simply fall apart or refuse to assemble.

When it does work, the result has a quality that varied-piece burrs cannot match: there is nothing to look up, nothing to label, and no way to cheat by recognising a piece. Everything you need to know is in the geometry of one stick, repeated.

How Hard Is It Next to a Six-Piece Burr?

Harder to start and easier to finish, which is the reverse of most people's expectation.

A six-piece burr gives you a foothold quickly. One piece is looser than the others, you find it within a few minutes of systematic pressing, and from there the puzzle unravels. The difficulty is concentrated in the opening move.

The Altekruse inverts that. There is no foothold at all until you stop treating it as a burr, and once the halves part the remaining pieces come away readily because they are all the same. Nearly all the difficulty sits in one conceptual step rather than being spread through the solve.

That makes it a poor puzzle for someone who wants a long dismantling sequence and an excellent one for someone who enjoys a single idea they have to arrive at. It also means the second time you meet an Altekruse it is barely a puzzle, which is the honest cost of a design built on one insight.

What Do We Make That Is Like This?

We do not make an Altekruse, and the closest things we do make are the notched interlocking crosses it is related to.

6-Piece Cross is the standard form, with a walkthrough, and 3-Piece Cross is the gentler version. Neither works the Altekruse way, because both have a key piece, which is exactly what makes the comparison instructive.

For the designer connection, Stewart Coffin's shelf is here, and the wider range is mechanical puzzles.

Frequently Asked Questions

What is the Altekruse puzzle?

A twelve-piece burr in which every piece is identical, each cut with three notches. Assembled it forms a symmetrical cross. It was patented by William Altekruse in 1890.

How do you take an Altekruse puzzle apart?

By sliding two complete halves against each other in opposite directions. There is no key piece, and no individual piece can be removed until the two sections have separated. Press on a whole face rather than on single sticks, and try each of the three axes.

Why does the Altekruse have no key piece?

Because it separates in halves rather than one piece at a time. In a normal burr one less-notched piece frees the rest; here the whole assembly splits along an axis first, which is why burr experience can actively mislead you.

What does the name Altekruse mean?

Old cross, in German. The family was Austrian-German and William Altekruse emigrated to the United States in 1844 with three brothers to avoid conscription. He went on to patent a cross-shaped puzzle.

Can an Altekruse be made with more than twelve pieces?

Yes. Stewart Coffin established that the same piece also assembles as a fourteen-piece version, and larger builds of thirty-six or thirty-eight pieces are possible.