Three Cube Puzzle

The goal of this puzzle is to make three cubes from the given pieces. The designer of this puzzle is Kohno Ichiro from Japan. Although this puzzle only has three pieces, the solution was pretty challenging for a couple of my test subjects. As for the build, I used scrap wood and purchased magnets. The total material cost was about $1.00 per puzzle. For the non-woodworkers, I've also included STL files for 3D prints.

This video shows the solution

Tools:

• Saw (Table, Miter or Hand)
• Drill
• 3/16" Drill Bit
• Ruler
• Pencil
• Wood clamps

Materials:

• Wood: 1" Wide x 7" long x 1/2" thick
• Magnets: 5mm diameter x 2mm thick
• Wood Glue

The parts are pretty simple. Cut the 1/2" thick piece of wood into 1" x 1" sections. You will need 6 pieces. I made extras since I usually screw something up during builds.

For the cuts, I used a table saw. A miter or hand saw would work as well.

As with the size of the puzzle, the size of the magnet is somewhat arbitrary. Based on my 1" cubes, I figure 5mm diameter magnets would fit reasonably well. Note that 5mm is approximately 0.197 inches. Since I wanted a press fit, I drilled the holes to 3/16" (.188"). Note that I made two versions of the puzzle. The first was from poplar (softwood) while the second was from walnut (hardwood). The 3/16" hole turned out to make a perfect press fit for the hardwood. For the softwood, I had to add a little epoxy into the hole to guarantee the magnet wouldn't come out.

Using a straight edge, mark lines from corner-to-corner to find the center of the block.

Use a center punch to aid in drilling. I used a 3/16" bit and drilled the depth per the drawing.

Magnet polarity is key to this puzzle. Unfortunately, I'm not going to explain this step very well. I actually built the puzzles with different arrangements and both worked. I used this arrangement on the poplar and 3D print and I'm happy with it.

You will have 3 pieces (A, B & C). Place the parts on a table as shown. The four magnet locations are called out as 1-4. Orient the magnets per the table. Note that "+" or "-" is referenced from the outer side of the block.

Place the magnet in the hole. Use a wood block or any other hard surface to press the magnet into the hole. I used a small dowel to sink it slightly below the flat surface. If in doubt about the fit, add a little epoxy in the hole before inserting the magnet.

I suggest building the puzzle up without gluing the sections together to verify everything will go together. Mark the parts with a sticker as A, B & C. Once you are sure everything goes together, proceed with gluing.

All the parts are the same. You will need to print 3 pieces. Two STL files are included. One has a 5mm hole while the other is slightly oversized (5.1mm). If the 5mm is too loose, use a little epoxy before inserting the magnets.

The red, green and yellow show the solution. Note that you might need to shuffle the parts around due to magnet polarity.

These were printed with the 5mm hole. Inserting the magnets was a little challenging.

This type/thickness of wood is generally available at most big box hardware stores.

Walnut is more expensive. I made this from a piece of scrap.

This was a fun project to make and I'm happy with how it turned out.

Thanks for viewing!