A chart line recording a probe's deviation as it runs up a tooth profile or along the face, magnified so microns show as millimeters on the plot. Experienced readers see slope, crowning, tip relief, scallops and waviness at a glance and know which machine setting to adjust. Traces are usually taken on several teeth spaced around the gear, on both flanks.
Lead trace shows only half the crown the print calls for, bump the crowning in the grind program and run another piece.
Also heard as
- chart
- profile trace
- lead trace
- K chart
Related terms
Gear checker
Shop name for a gear measuring machine that traces profile, helix, pitch and runout, and for its operator.
Profile deviation
How far a tooth's actual shape from root to tip departs from the intended involute and modifications.
Helix deviation
How far a tooth's actual path across the face width departs from the intended helix, including crowning.
Scallops
Shop word for the small ridges a hob leaves across and along each tooth flank, visible as a fine texture.