The arc width of a tooth measured on the pitch circle, nominally half the circular pitch. In practice teeth are cut thinner than nominal by a specified amount so the pair runs with backlash, and the tolerance on this thinning controls how much backlash results. Because arc thickness cannot be measured directly, it is checked indirectly by span measurement, measurement over pins, or a gear tooth caliper reading chordal thickness.
Tooth thickness is on the high side, over pins reads two thou big, so lash at assembly will be tight.
Also heard as
- circular tooth thickness
- arc tooth thickness
Related terms
Backlash
The play between mating teeth: how far one gear can rock before its teeth contact the other gear's teeth.
Measurement over pins
Measuring across precision pins or balls placed in opposite tooth spaces to check tooth thickness.
Span measurement
Checking tooth thickness by measuring across several teeth with a disc micrometer.
Circular pitch
The arc distance from one tooth to the same point on the next tooth, measured along the pitch circle.