Classic "Wooden" Puzzle - With Magnets!

Hey all! I wanted to see if I could use Autodesk Fusion to design a classic wooden puzzle to be 3D printed. You might've seen these before, maybe in the magic shop at Pier 39 in San Francisco or in a Barnes and Noble. I thought it'd be an interesting challenge to model since the geometry is complex, and I wanted to embed some magnets to help it stay together.

For anyone who wants to print one, I've included the STL file, but I encourage you to give modeling it a go - it was quite the puzzle in itself!

Since this is a 3D printed project, the necessary supplies here are pretty straightforward. All you need is:

• Access to a 3D printer
• Your choice of filament(s)
• Some 8x3mm magnets (24 to be precise).

I had an idea of what I wanted, but I had to examine the geometry of the puzzle before I could model it to be 3D printed.

I googled "wooden puzzle" to find the right shape, then "12 point 3D star" to get a more precise idea. I found that the shape is technically called the first stellation of the rhombic dodecahedron, or Escher's Solid. What I noticed is that it's made of a bunch of square pyramids, whose heights are half the width of the base. Once I figured that out, I was confident enough to begin modeling.

Using 2 sketches and a loft, I made a square pyramid and mirrored it to create the first of 3 octahedrons, making sure to center it about the origin. Then, I copied and rotated the body about the origin axes. After adding some color, we're left with a preliminary model of the puzzle.

Since these bodies are overlapping, our current shape can't actually exist in real life, so it has to be modified. Creating a sketch on the side of the yellow octahedron and projecting the edges of the blue one allowed me to create a construction plane at their intersection. I used it to lop off the top of the yellow one with a split body, mirroring the change on the other side and removing the extra bodies created. I also removed the blue and brown bodies, opting to copy and rotate the yellow one a couple times again to update the shape.

With just the yellow and blue bodies visible, I could see things start to come together. I cut the blue's shape out of the yellow with the combine body tool. Interestingly, this results in a single body instead of 2 because the corners are still touching. Despite that, I couldn't split it with an origin plane to make it into 2 bodies with an origin plane since the intersection is infinitely small. As a workaround, I created a sketch with a rectangle and extrude-cut one side away.

We're now left with a single piece that's ready to be mirrored, copied, and rotated again. There's no overlap left, but we can see with a section analysis that there's a cube-shaped hole in the middle now.

There's 6 pieces and a cube-shaped hole in the middle of them, which makes filling the hole pretty straightforward. I rolled the timeline back to before copying the piece, that way any changes I made would update the rest of the pieces. By lofting the inside face to the origin, we create another pyramid shape that, once copied, will fill the cube-shaped hole.

Now we've got Escher's Solid modeled with 6 individual pieces and no overlap. However, it's not quite ready. Since it's modeled to be geometrically perfect, there's no clearance, which means the pieces won't fit together in real life. But we're making progress!

Adding clearance to this shape was harder than you might think. I couldn't offset the faces of a piece without cutting into it in a weird way. But, now that I understood the shape, I realized it was easier to model than I'd initially thought. I decided to start over. I sketched a new shape, making sure to add clearance. Note the corner in the top right of the sketch does not line up with the rectangle. I extruded it upwards, drafted the faces at 45 degrees, and mirrored the body. Despite starting from scratch, getting back to this point took under 5 minutes.

When embedding magnets into a 3D print, it's important to take the printing process into account to avoid a crash. We'll pause the print at the right time, then put a magnet in before resuming. The hole for a magnet has to be the right shape for it to be inserted and deep enough so it can be printed over. If the magnet is sticking out when a print is resumes, it will crash.

I rotated the body to the orientation it will be printed in to make things easier on myself. Adding the holes was relatively straightforward. I placed a sketch on each of the 4 faces of the "inner pyramid," then used an offset extrude-cut to make a hole on the inside of the part. One thing to note is that each hole had to have a horizontal layer above it to be bridged over during the print. I achieved this with a draft where necessary.

After rotating the body back into place, rounding over the edges with a filet, and copying the bodies back for the sake of completion, we're ready to print!

I wanted 3 colors in my final puzzle, so I decided to print 2 pieces at a time. After slicing, I added pauses at the right layers.

During the print, I was very careful to orient the magnets in the correct direction. The "A" sides of each piece need to have one pole of the magnet facing out, while the "B" sides need to have the other pole facing out.

Each of 3 prints had 3 pauses for magnet insertion, so I had to come back to the printer pretty often. Once they were done though, they were ready for assembly!

All done! This was quite an interesting challenge and I enjoyed iterating on my model to be as clean as possible. The final result is quite satisfying to play with. The pieces come together magnetically with a nice "clack" and don't fall apart. Overall, it makes for a fun desk toy and/or paperweight.

Here's a couple videos of me solving and disassembling the puzzle, comparing versions with and without magnets.