This is how glass is cut into circle People typically use a glass cutter, which is a tool specifically designed for cutting glass. The glass cutter has a small, sharp wheel that scores the glass when it is rolled along the desired cutting line. The scored line weakens the glass, making it easier to break along the intended shape. Additionally, a compass or a circle-cutting guide may be used to mark and guide the cutting line in a precise circular shape. A sandpaper or a glass file is used to smo