A deliberate radial offset of the generating rack or hob from its standard position, expressed as a coefficient x times the module. Positive shift moves the working profile further up the involute, thickening the root and avoiding undercut on small pinions; negative shift does the reverse. Designers use it to balance strength and sliding between pinion and gear and to fit a pair to a non-standard center distance.
It's a 12-tooth pinion with plus point four profile shift, so don't measure OD against a standard chart and call it wrong.
If a gear's outside diameter doesn't match the chart, suspect profile shift before calling the part wrong.
Also heard as
- addendum modification
- x coefficient
- rack shift
Related terms
Undercut
A notch cut into the base of small-pinion teeth when the generating tool removes part of the working involute.
Addendum
The radial height of a gear tooth above the pitch circle, normally one module for a standard tooth.
Center distance
The distance between the axes of two meshing gear shafts, set by the housing bores.
Tooth thickness
How thick a gear tooth is along the pitch circle, the dimension that is thinned to create backlash.