TO THROW OUT OF GEAR

To throw out of gear is to lose, accidentally or voluntarily, the engagement between two wheels of a Gear, which interrupts the transmission of the Movement. Accidental throwing out of gear occurs when the teeth stop engaging correctly: they slip, jump or overlap instead of driving each other. The main causes are an incorrect distance of centres (wheels too far apart), excessive height play allowing the wheels to move axially, a broken or deformed tooth, a Bridge incorrectly positioned, or a shock. The consequences range from a temporary jolt to a complete stoppage of the Movement, as well as accelerated wear of the teeth. Throwing out of gear is a defect sought during inspections and decottage, as it reveals a problem of geometry or holding of the wheels. Prevention relies on respecting the Distance of centres, the control of play (axial clearances), the good condition of the bridges and the integrity of the teeth. The term illustrates the precision required of the Train (wheel train): a few hundredths of a millimetre difference are enough to compromise the meshing.