Chairpanzee Analog Computer

$ 16.00

Chairmaking is complex enough without having to worry about the trigonometry used to calculate the drilling and sighting angles for a chair’s legs and spindles.

The Chairpanzee does all the math for you with its 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. The Chairpanzee calculates the sighting angle. Flip the Chairpanzee over, and you’ll see the drilling angle (called the “resultant”) displayed.


The Chairpanzee is ideal for anyone who works with compound angles for chairs, stools and tables. With the Chairpanzee, you can:

  • Use photos of antique pieces to calculate the sightline and resultant angles so you can copy a classic piece, or merely swipe the angles for your own interpretation.
  • Use construction drawings or models (we make models with wire clothes hangers for the legs) to design entirely new pieces of furniture and easily figure out how to drill the compound mortises.
  • Learn the relationship between rake and splay at a deeper level than plugging numbers into an equation. The Chairpanzee shows you how small changes in rake and splay cascade through a design. Sometimes small changes make little difference. Sometimes they make huge differences.
The Chairpanzee was developed by Ed Sutton at FirstLightWorks in the U.K. and is printed and assembled in the United States. The Chairpanzee 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 the Chairpanzee are printed on both faces of the tool, so you’ll never lose the instruction manual. The following video shows the tool in use.


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