Gears

These days almost all gears use the involute profile or a derivative of the involute profile. A modern gear box for a road vehicle can be expected to work without repair for at least 150,000 miles (200,000 km). The working faces of the teeth on gear wheels are curved and slide one over the other during contact. The gears work in a bath of oil and inevitably there will be wedge action to keep the teeth mechanically separated. We now know that these long working lives result from accurate profiles for the teeth and very good finishes.