Gearbox and Gear Balancing

Rotating elements of a gearbox

Within a gearbox, the following components require balancing:

  • The input shaft with its driving gear
  • Intermediate shafts (in multi-stage gearboxes)
  • The output shaft with its driven gear

Key point: A gear wheel is not a symmetrical component. Balancing a shaft together with its gear means the eccentricity of the toothed rim has to be taken into account.

Gearbox balancing challenges

1. Gear eccentricity

If the centre of mass of the toothed rim does not coincide with the shaft axis, an imbalance of the "gear run-out" type develops.

Symptoms in the spectrum:

  • A strong gear-mesh frequency (GMF)
  • Sidebands around the GMF spaced at 1× running speed

2. Tooth wear

Uneven tooth wear changes the distribution of mass.

3. Shaft bending

Overloading or an impact can bend a shaft, creating imbalance and misalignment at the same time.

Balancing gearbox shafts

Method: on the machine bench

Procedure:

  1. Strip down the gearbox
  2. Remove the shafts
  3. Clean and inspect for defects
  4. Balance each shaft as an assembly with its gear
  5. Grade G6.3–G16 (depending on the type)

Correction specifics

  • Drilling into the body of the shaft (away from the loaded zone)
  • Drilling into the hub of the gear
  • Grinding the end faces (for small corrections)
💡 Important: Never drill into the toothed rim or near the bearing seats!

Conclusion

Balancing gearbox shafts is a specialist operation carried out during a major overhaul. A correctly balanced gearbox runs quietly and free of vibration, and its service life increases two- to three-fold.

Gearbox balancing

Equipment and services for balancing gearbox shafts

The Balanset-1A instrument

An instrument for gearbox vibration diagnostics and fault finding

Buy the instrument

Bench balancing

Balancing gearbox shafts on specialist machines

Order the service