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# O’Beirne’s Cube

Much of what we make is two-dimensional. Hugh Montgomery, a mathematician at the University of Michigan, told us about an intriguing 3D dissection puzzle by Tom O’Beirne, a Scottish author and inventor of puzzles. O’Beirne’s cube consists of six pieces that can be packed into a box. The blocks seem irregular at first glance.

However, the pieces are built from four copies of the base component: a 3x4x6 rectangular prism, or cuboid. In our version, each unit in the base cuboid is 0.25 inches, or a bit over 6 mm wide.

O’Beirne combined two of these 3x4x6 cuboids on a matching face, to produce these doubled cuboids:

He then created every possible pair of the doubled cuboids, matching half of a face on each. Below, you can see how a 3x4x12 is paired with a 4x6x6. There are two ways to do this. They are mirror images of each other.

There are three possible pairings of the doubled cuboids. Each pairing produces two mirrored pieces. This generates the six blocks of O’Beirne’s puzzle.

You can combine these six to make a cube.

You can rearrange the six pieces into five other cuboids:

In fact, with any one of the these six cuboids, you can split it into two parts, and recombine to create another cuboid. You can quickly cycle thorugh all six! The original version of the diagram below is described in more detail in Brian Butler’s excellent article on John Rausch’s puzzle site.

You don’t have to limit yourself to cuboids. Here are some other puzzling shapes.

We sell the O’Beirne’s Cube here. But if you have the tools and are up for it, you can make your own. At the San Francisco American Craft Council show, we met Ron Choy, who was captivated by the O’Beirne’s cube. I sent him the link to John Rausch’s site. We were delighted to hear from Ron later, with a picture of the cube he made along with his notes on the process. Now that’s some hands on learning!