A shop-floor way to check tooth thickness: hardened pins or balls of a calculated size are placed in tooth spaces on opposite sides of an external gear, or inside an internal gear, and the distance over or between them is measured with a micrometer. The reading is compared with a value calculated from the design tooth thickness. On odd tooth counts the pins cannot sit directly opposite, so the calculation corrects for the offset.
Measurement over pins reads 4.2365, calculated max is 4.2350, so the teeth are thick, take another skim and bring it down two thou over pins.
Use a matched pair of clean pins of the calculated size; a burr or a wrong pin reads as a fat or thin tooth on the whole gear.
Also heard as
- MOP
- over pins
- over balls
- MOW
- dimension over wires
Related terms
Tooth thickness
How thick a gear tooth is along the pitch circle, the dimension that is thinned to create backlash.
Span measurement
Checking tooth thickness by measuring across several teeth with a disc micrometer.
Backlash
The play between mating teeth: how far one gear can rock before its teeth contact the other gear's teeth.
Green
Shop word for a gear in its soft, machined state before heat treatment, as in cut green, finish hard.