GMF stands for gear mesh frequency, the rate at which teeth engage, calculated as the number of teeth on a gear times its rotational speed in revolutions per second. A 30-tooth pinion at 1,800 rpm meshes at 900 Hz. Vibration analysts watch the GMF peak and its harmonics, and sidebands spaced at shaft speed around it point to eccentricity, runout or a damaged tooth on that shaft.
Big sidebands around GMF spaced at pinion speed, so it's the pinion, probably runout or a cracked tooth.
Divide a peak by shaft speed to get its order; an order equal to a tooth count tells you which gear is talking.
Also heard as
- gear mesh frequency
- tooth mesh frequency
Related terms
Mesh
The engagement of two gears' teeth, or the zone where they meet; also the verb for gears engaging.
Transmission error
The tiny difference between where the output gear actually is and where a perfect gear pair would put it.
Whine
A steady, pitch-changing tonal noise from gears, rising with speed and caused by tooth meshing errors.
Ghost frequency
A gear noise tone that matches no tooth count in the box, left behind by errors in the cutting machine.