The main drawback is that hey spur gear will vibrate. Whether due to the design, manufacture or　deformation, etc., at the same time along the entire tooth surface may occur some changes involute shape. This will lead to a regular, once per tooth incentive, it is often very strong. The resulting vibration causes a large load on both the gear and causing a noise. Another drawback is that the contact time of two times by the additional strength obtained by the engagement of the teeth can not be used, because the stress is single tooth meshing cycle defined condition.

The helical gear can be regarded as a dislocation of the sheet should be placed into gear spur gear, so that each contact piece is in the different parts of the tooth profile, resulting in a compensating effect of each wafer gear error, because the compensation of wheel the teeth of the elastic very effective, so that the results obtained, the error is less than 10mm in the tooth so that the error can be an averaging, which under load conditions, if the error can be within 1mm of the tooth as smooth operation. Because any transient, about half of the time (assuming overlap of about 1.5) will have two meshing teeth, which provide additional benefits in terms of strength. Therefore, stress can be created in 1.5 times the tooth width, rather than a tooth width of the base.

Manufacturing and assembly bunch of flakes spur gear is both difficult and uneconomical, and therefore manufactured fused, the teeth of the gear along the helix direction. Helical gear is not as straight gears, it will result in poor axial force. But the benefits in terms of vibration and strength far better than the shortcomings brought by the axial thrust and a slight increase in manufacturing costs brought. So use a helical gear reducer rather than spur gears in the manufacture of such four series:. R Series coaxial helical gear reducer, K series helical bevel gear reducer, S series helical worm gear reducer, F series parallel shaft helical gear reducer

Note: What is the spur gears: spur gear teeth are parallel to the shaft gear. We have only discussed the theory of parallel shaft gear transmission, so any money perpendicular to both of the gear shaft are identical in cross section.