# Thales Square

 Project by Woodknack posted 05-15-2016 05:47 AM 5197 views 45 times favorited 31 comments

Heard about these for the first time today and decided to make one. I don’t know what they are called but the person I learned them from called them a Thales Square, after Thales theorem.

Basically you take two sticks, the longer one represents the diameter of a circle and the shorter represents the radius. When you place this apparatus in a corner it will tell you immediately if the corner is square. If all three points touch, the corner is square. If the two outside points touch, the angle is acute. If the center + one outside point touch, the angle is obtuse. As long as all 3 points are equidistant from the center, the tool is highly accurate.

If you make one and play with it, you’ll intuitively understand it pretty quickly. I made the center piece (radius) first, drilled holes and attached it roughly halfway on the longer piece (diameter). Then swing the short stick to each side and use a sharp chisel to chop off each leg to the exact length of the center piece. Hopefully that makes sense. It was really easy. It literally took about 5 minutes to make.

-- Rick M, http://thewoodknack.blogspot.com/