The helical gear reducer can be regarded as a cylindrical gear formed by dislocation of a group of thin-toothed gears, so that the contact of each piece is at different parts of the tooth profile, thereby compensating for the error of each piece of gear. This compensation is effective due to the elasticity of the gears.
Therefore, a gear with an error of less than 10mm can average the error and thus run as smoothly under load as a gear with an error of less than 1mm. Because at any one time, about half the time (assuming a coincidence of about 1.5) there will be two teeth meshing, which gives an additional benefit to strength. Therefore, the stress can be based on 1.5 times the tooth width instead of one tooth width.
The main disadvantage of spur gears is vibration. Whether due to design, manufacture, or deformation, changes in involute shape can occur along the entire flank at the same time. This results in a regular, once-per-tooth stimulus, often very strong. The resulting vibration not only places a heavy load on the gears, but also produces noise. Another disadvantage is that sometimes the additional strength obtained from the meshing of two pairs of teeth cannot be used during the contact time because the stress is limited by the meshing of a single tooth in the cycle.
It is difficult and uneconomical to manufacture and assemble a large number of lamellar spur gears, so manufacturing the gears in one piece is in the helical direction. Unlike spur gears, helical gear reducers cause differential axial forces. But the benefits of vibration and strength far outweigh the disadvantages of axial thrust and a slight increase in manufacturing cost. Therefore, helical gears are selected instead of spur gears in the manufacture of reducers. For example, R series coaxial helical gear reducer, K series spiral bevel gear reducer, S series helical worm gear reducer, F series parallel shaft helical gear reducer.