Abstract: The invention achieves a method and a device for providing infinitely variable adjustment to the throw of an eccentric from zero to a maximum while the eccentric is permitted to continuously travel in angular motion. This is achieved by two juxtaposed and eccentric members mounted on a drive shaft, one (the outer) overriding, the other (the inner). The eccentric members may be relatively positioned by a control shaft, which extends coaxially through the drive shaft, and gearingly mates with the outer eccentric member. The outer surface of the outer eccentric can be arranged (by relatively positioning the outer and inner eccentric members) to trace the loci of points of a circle, whereupon no reciprocation takes place, or of a family of ellipses of varying eccentricity, whereby reciprocation is achieved in correspondence to the relative eccentricity in the path of travel of the outer surface.