## 21 Jan Laying Out a Circle

**Old time carpenters were able to use framing squares to do amazing design work. They were able to draw perfect circles with a framing square without using the center point of a circle.**

**Challenge: ****Draw a 6 inch diameter circle on a piece of OSB using a framing square without using the center point of the circle.**

**Materials: scrap OSB board, 2 nails, 1 framing square per pair**

**Procedure: Students are given the materials to draw a 6 inch diameter circle using a framing square. Remind students they need to use both nails. Remind students they cannot use the center point of the circle. Allow time for students to play and experiment.**

**Once students find the “method” of drawing a circle, they need to provide geometric reasoning for why this works.**

Solution: Tack two nails to set the diameter you want, then rotate a framing square against the nails while you hold a pencil in the corner of the square (see photo below). A right angle is inscribed in a semi circle.