Principles for selecting the number of teeth of precision gears:
1. The closed precision gear transmission generally has a high speed. In order to improve the stability of the transmission and reduce the impact and vibration, it is better to have more teeth. The number of teeth of the pinion can be taken as z1=20~40. Open (semi-open) gear transmission, because the gear teeth are mainly worn out, in order to prevent the gear from being too small, it is not appropriate to use too many teeth for the pinion, generally z1=17~20.
2. When the two gears are meshed, the tooth tip of one gear always enters the tooth root of the other gear. In order to prevent thermal expansion from being dead and to have space for storing lubricating oil, the tooth root height is required to be greater than the tooth tip height. To this end, the addendum height coefficient and the top clearance coefficient are introduced.
3. The number of teeth of the pinion should avoid undercutting, the meshing teeth should preferably be prime numbers, and the need for matching and rounding the center distance should also be considered.
Materials for manufacturing precision gears:
The steels commonly used in the manufacture of precision gears are quenched and tempered steel, quenched steel, carburized and quenched steel and nitrided steel. The strength of cast steel is slightly lower than that of forged steel, and is often used for gears with larger sizes; gray cast iron has poor mechanical properties and can be used in light-load open gear transmissions; ductile iron can partially replace steel to make gears; plastic gears are mostly used In places where light loads and low noise are required, steel gears with good thermal conductivity are generally used for their matching gears.
In the future, precision gears are developing in the direction of heavy load, high speed, high precision and high efficiency, and strive to be small in size, long in life and economical and reliable.