Fracture of a whole tooth or part of one. Bending fatigue is the most common type: a crack starts in the tension-side root fillet, grows with each cycle leaving beach marks, and the tooth breaks off when the remaining section is too small. Overload breakage is a single event with a rough, fibrous surface. Causes include high bending stress, edge loading, grind burn in the root and foreign objects through the mesh.
Tooth breakage started at the root fillet, beach marks all the way across, so it's fatigue, not the jam last week.
Read the fracture face: beach marks mean fatigue that built over time, a uniformly rough face means one big overload.
Also heard as
- broken tooth
- tooth fracture
Related terms
Bending stress
The tensile stress in the root fillet of a loaded tooth, which decides whether teeth break off.
Shot peening
Blasting gear roots with hard steel shot to build compressive stress and raise bending fatigue strength.
Edge loading
Tooth load piling up at one end of the face width because of misalignment or deflection.
Idler
A gear placed between a driver and a driven gear to change direction or span distance, without changing ratio.