The performance of any gear pair will depend to a very large extent on the accuracy with which they have been manufactured. This accuracy is dependent on the methods, tooling and skill used to produce the gears.
Quiet operation with minimum vibrations can only be achieved when the gears transmit uniform angular velocity after being properly mounted in their running position. This condition is only obtained when both of the gears have been made accurately and correctly assembled. In worm gearing the minor inaccuracies of the softer material mating gear, normally the wheel, are naturally corrected by the harder gear after a running-in period.
The load capacity and life of the gears are influenced not only by precision, but also the quality of the finished flank surface. Inaccuracies result in dynamic overloads on the teeth, these loads rising in proportion to the increases in speed. Much though has been given to the problem of improving the area of tooth contact and one solution has been to reduce the manufacturing tolerances. The high-quality tolerances DIN/ISO 2, or the generally considered equivalent AGMA 14, can be achieved with present day tooling. Commercial gearing is usually expected to be produced to DIN/ISO 6, or their equivalents AGMA 10, JIS 3, or BS B.