Wooden Icosahedron Earth Puzzle

thingiverse

This 20-piece earth puzzle will put your geography knowledge to the test! It's also a fantastic challenge to tackle. The model shown here is crafted from Eastern Maple. This wooden puzzle is an adaptation of the printable Earth Puzzle found on Thingiverse at https://www.thingiverse.com/thing:4153383. The .stl files have been modified for use with a CNC router. The files are organized into "N," "NE," "S," and "SE" groups, each containing five puzzle pieces. Pieces labeled "N" share a vertex near the north pole in the Bering Strait area. "NE" pieces all share an edge with an "N" piece, while pieces labeled "S" share a vertex near the south pole. "SE" pieces all share an edge with an "S" piece. The files are provided separately and can be grouped and arranged according to your software and router setup preferences. It's recommended that you mill the pieces in such a way that the wood grain wraps around the globe like lines of latitude. If you examine each .stl file closely, you'll notice that one vertex has a greater fillet than the others. The edge opposite this vertex should be oriented in the same direction as the grain. A 1/4" end mill bit was used for adaptive clearing followed by a 1/4" round nose bit for contouring. When milling, it's essential to be precise when cutting edges, or the pieces won't fit together to form an icosahedron and the land masses may not align correctly. The inner triangular edges of the finished pieces should measure exactly 50mm at an angle of 69.1 degrees from horizontal (the dihedral angle of an icosahedron is 138.19 degrees). The pieces are designed with a few millimeters of overlap that will be removed when making the angled cut. Using a tablesaw and sled to position and hold the pieces is recommended, and two .dxf files have been included to assist with this process. These files can be cut from 1/8" MDF using a laser cutter. The "Cut marker and Adapter insert" file consists of two pieces: an outer triangle that is placed over the back of the wooden piece and scored through the slots to indicate where cuts should be made, and an inner triangle attached to the piece with double-sided tape, used to hold and rotate the piece within the sled adapter for each cut. The "Sled Adapter" has a triangular hole that accepts and holds the triangle attached to the wooden piece. The surrounding shape is what fits my tablesaw sled; you may need to modify this as necessary. Magnetic support structures are critical for holding and aligning the pieces, so it's essential to place them precisely and normally to the edge surface. The "CNC Earth Magnet Hole Drill Jig" .stl file has been included to help with this process, made to accept drill guide inserts such as those found at https://www.leevalley.com/en-ca/shop/hardware/jig-and-fixture-parts/101378-drill-guide-insert. The magnets should be inserted with opposite polarity on each edge, maintaining the same pattern around each edge and across each piece. A dab of glue can be used to hold the magnets in place. After assembly, some sanding will be necessary. The finished pieces were completed with a few coats of shellac. You can see a video of this project at https://youtu.be/wrwjbiOyeqo. If you decide to undertake this project, please share your pictures and let me know!