Math Monday: Four Triangles Again

By George Hart for the Museum of Mathematics


Last week’s Math Monday column looked at a tricky construction of four equilateral triangles. Let’s revisit it, but instead of using paper, we’ll use square sticks. These twelve identical wood parts fit together using 60-degree half-lap joints.

This wood version is made from 3/8 inch square stock, with slots cut as indicated below. It is easy to make these with a table saw or radial arm saw. Assembling them so each triangle links symmetrically with the other three triangles is the tricky part.

Alternatively, you can make the components on a 3D printer. Then the lap joints don’t need to be cut. They are formed as the piece is built up. If you have access to a 3D printer, you can make your own copy using the STL file available here.

See all of George Hart’s Math Monday columns

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Gareth Branwyn is a freelance writer and the former Editorial Director of Maker Media. He is the author or editor of over a dozen books on technology, DIY, and geek culture. He is currently a contributor to Boing Boing, Wink Books, and Wink Fun. His free weekly-ish maker tips newsletter can be found at

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