1-9 Gear Noise

This figure indicates the results of a survey conducted by a manufacturer that produces
gears for automobile, machine tools and speed reducers.

cause of vibration
Cause of noise and vibration :

  1. Accuracy of gears
  2. Accuracy of assembly
  3. Tooth surface finish
  4. Configuration of gearbox
  5. Lubrication of gears
  6. Bearing
  7. Material of gears
  8. Design of gears
  9. Motor and variation of load
  10. Driving condition
  11. Shaft and shaft alignment
  12. Configuration of gears
  13. Wear of gears
  14. Surface damage on gears
  15. Others


Broken down by the factors contributing to gear noise, it becomes :

  • Design………………………35%
  • Fabrication………………30%
  • Usage………………………..20%
  • Assembly………………….15%


Causes (Items assumed to have effects on noise) :

  • Bad tooth contact
  • Large pitch error
  • Large tooth profile error
  • Oscillating torque load on the gear shaft
  • Poor tooth surface finish
  • Center distance is too small
  • Rotation is too fast
  • Ball and roller bearings are causing noise
  • Gearbox is amplifying noise
  • Deformation of gear due to heat treating


In order to manufacture gears that minimize noise during operation :

  • Reduce the pitch error
  • Reduce the tooth profile error
  • Reduce the runout error
  • Reduce the lead error
  • Modify tooth surface by crowning
  • Tip relieving may correct pitch error from tooth deformation
  • Remove sharp corners of tooth by chamfering
  • Eliminate the roughness on the tooth surface
  • Increase the contact ratio – bigger contact ratio lowers the noise
  • Try to design gearboxes as close to round shape as possible
  • Use a flexible coupling between the prime mover and the gearbox
  • Machine the mounting holes of gearbox precisely so that gears can be mounted accurately
  • When assembling gears into gearbox, care must be taken that gears come in contact properly – to avoid edge contact


To improve surface finish, gears are generally shaved or ground. Spiral bevel gears are lapped or ground.
crowning examplechamfering example
Left : Crowning of tooth
Right : Chamfering of tooth

edge contact example
Example of edge contact

This figure shows an example of data regarding noise level as a result of test on KHK stock gears.
▲ – ▲ : S45C without heat treatment
(SS2.5-24, SS2.5-48)
△ – △ : Plastic
(PS2.5-24, PS2.5-48)
● – ● : S45C Tooth surface high-frequency induction hardened and ground
(SSG2.5-24, SSG2.5-48)
○ – ○ : SCM415 Overall carburizing and quenching, tooth surface ground
(MSGB2.5-24, MSGB2.5-48)

noise level of gears
Noise level of KHK stock gears  1984 – 1985
Vertical line – Decibel (db)
Horizontal line – n 1(rpm)

Related links :
Spur Gears – Main page of spur gears
How to reduce Gear Noise – A page of Gear Technical Reference