Tooth profile Gear

a profile 1 side of tooth in cross section between outside circle , root circle. profile curve of intersection of tooth surface , plane or surface normal pitch surface, such transverse, normal, or axial plane.

the fillet curve (root fillet) concave portion of tooth profile joins bottom of tooth space.

as mentioned near beginning of article, attainment of nonfluctuating velocity ratio dependent on profile of teeth. friction , wear between 2 gears dependent on tooth profile. there great many tooth profiles provides constant velocity ratio. in many cases, given arbitrary tooth shape, possible develop tooth profile mating gear provides constant velocity ratio. however, 2 constant velocity tooth profiles commonly used in modern times: cycloid , involute. cycloid more common until late 1800s. since then, involute has largely superseded it, particularly in drive train applications. cycloid in ways more interesting , flexible shape; involute has 2 advantages: easier manufacture, , permits center-to-center spacing of gears vary on range without ruining constancy of velocity ratio. cycloidal gears work if center spacing right. cycloidal gears still used in mechanical clocks.

an undercut condition in generated gear teeth when part of fillet curve lies inside of line drawn tangent working profile @ point of juncture fillet. undercut may deliberately introduced facilitate finishing operations. undercut fillet curve intersects working profile. without undercut fillet curve , working profile have common tangent.