Rolling of Non-cylindrical Surfaces
Illustration showing that the rolling of non-cylindrical surfaces. "If the angular velocity ratio of two rolling bodies is not a constant, the pitch lines take, the conditions of pure rolling contact should be fulfilled, namely, the point of contact must be on the line of centres, and the rolling arcs must be of equal length.
Peter Schwamb, S.B. And Allyne L. Merrill, S.B. Elements of Mechanism (New York, NY: John Wiley & Sons, Inc., 1904)