Operating Pitch Circle
The operating pitch circle is the circle on which two meshing gears roll on each other without slip during operation. For standard gearing without profile shift it coincides with the reference circle; with a profile shift or altered center distance it deviates from it.
Definition
The operating pitch circle is a pairing-dependent quantity: it only arises when two gears mesh and is located where the circumferential velocities of both gears are equal. The contact point of the two operating pitch circles is the pitch point. The radius of the operating pitch circle depends on the center distance and the distribution of tooth numbers.
Distinction from the Reference Circle
The reference circle is a property of the individual gear (d = m·z) and does not change. The operating pitch circle, on the other hand, is a pairing quantity: for standard gearing (no profile shift, standard center distance) both coincide. If the center distance is increased or a profile shift is applied, the operating pitch circle moves outward and deviates from the reference circle. The operating pressure angle changes accordingly.
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