The total variation in radial position of a probe, ball or pin placed in each tooth space in turn as the gear rotates on its datum axis. It mostly reflects eccentricity between the teeth and the bore or journals, plus some pitch and profile effects. Runout makes backlash vary around the gear and produces sidebands spaced at shaft speed around mesh frequency, and it is often the first thing checked on a noisy gear.
Runout's eight tenths on the ball check, so the teeth weren't cut concentric to the bore, check the hobbing arbor.
A gear can pass every tooth check and still be noisy if its teeth run out to the bore; check runout first on a noise complaint.
Also heard as
- radial runout
- TIR
Related terms
Pitch deviation
Errors in tooth spacing, either from one tooth to the next or accumulated around the gear.
Double-flank test
Rolling a gear in tight mesh against a master gear and recording how the center distance varies.
Backlash
The play between mating teeth: how far one gear can rock before its teeth contact the other gear's teeth.
GMF
Gear mesh frequency: tooth count times shaft speed, the frequency at which teeth enter mesh.