A Chair-making Calculator To Find Leg Mortise Angles

Christopher Schwarz fans, and especially those who build or would like to build chairs, will find the new, low-tech, Chairpanzee Analog Computer both interesting and useful. Priced at $16 from Lost Art Press (and Chris is a partner in that company), this handy little tool is designed to do the math that is used to calculate the drilling and sighting angles for a chair’s legs and spindles. That is, it tells you what angle to drill the leg mortises. This is a simple, no-math-needed interface. Simply slide the tool’s interior card so the splay you desire appears in its top window. Choose the rake you wish in the window below and the Chairpanzee calculates the sighting angle. Flip the Chairpanzee over and you’ll see the drilling angle. This is an ideal tool for anyone who works with compound angles for chairs, stools and tables. With it one can use photos of antique pieces to calculate the sightline and resultant angles to copy a classic piece, or merely swipe the angles for your own interpretation. A woodworker can use construction drawings or models to design entirely new pieces of furniture and easily figure out how to drill the compound mortises. Or one can learn the relationship between rake and splay at a deeper level than plugging numbers into an equation. The Chairpanzee shows how small changes in these values cascade through a design. Sometimes small changes make little difference, but sometimes they have a huge impact. The Chairpanzee was developed by Ed Sutton at First Light Works in the U.K. and is printed and assembled in the United States. It is compact (4” x 9-1/4”) and durable – it’s printed on .024” board stock with a tough gloss coating. The exterior is glued and secured with metal eyelets. Instructions for using it are printed on both faces of the tool, so you’ll never lose the instruction manual. Here’s a video that shows the tool in use.