Crown gear

Crown gear used at a historic mill.

A crown gear is a gear where the teeth of the gear are not flat, but at an angle. The most common such angle is a right angle (90 degrees). The name crown gear comes from the facr that these gears look like crowns. Crown gears were widely used in antiquity and the Middle Ages. In modern times they were replaced by bevel gear. This is mainly because with bevel gear, the calculations are easier.