The distance between shaft centers of a parallel-axis gear pair, nominally half the sum of the pitch diameters. Running at more than nominal center distance opens backlash and raises the operating pressure angle, while running tight can bind the mesh. Involute gears keep a constant ratio when it changes slightly, which is why center distance tolerance is generous compared with other mechanisms.
Center distance on the rebored housing is four thou long, so backlash is up, go a little heavier on tooth thickness for the new set.
Also heard as
- CD
- operating center distance
Related terms
Backlash
The play between mating teeth: how far one gear can rock before its teeth contact the other gear's teeth.
Pitch diameter
The diameter of the pitch circle, the imaginary rolling circle on which tooth size and gear ratio are based.
Profile shift
Moving the cutter in or out from the standard position, making teeth fatter or thinner without changing pitch.
Double-flank test
Rolling a gear in tight mesh against a master gear and recording how the center distance varies.