The method for selecting the number of gear teeth in mechanical design is: the number of teeth should meet the requirement of no undercut; determine the gear ratio of the two gears according to the transmission ratio; the number of teeth of the two gears is preferably a prime number; the entire circumference of the gear The total number of teeth on the machine is called the number of teeth, generally represented by the letter z. In order to reduce the size and weight of the gear transmission mechanism, generally speaking, the number of teeth of the pinion should be the minimum number of teeth without undercutting (it can be one to three more teeth), and then the number of teeth of the other gear can be calculated through the transmission ratio . The gear ratio of the two gears is determined according to the transmission ratio; preferably, the number of teeth of the two gears should be prime numbers, such as 17, 19, 21, 23 and 27. The total number of teeth on the entire circumference of the gear is called the number of teeth, generally represented by the letter z. Each raised portion of a gear that engages is called a tooth. These bumps are arranged in a radial pattern. It is used to make contact with a similar raised portion on the mating gear, resulting in continuous meshing operation of the gear. Broken teeth refer to one or more teeth of the gear being completely or partially broken. It is usually caused by the alternating stress of the gear teeth exceeding the fatigue limit of the material.