Abstract: An indexing chuck assembly to hold a work piece so work may be performed on it in differently rotated positions, as on a lathe. The chuck block is rotated between a lifting arm and a table member, the bottom of the chuck block having a cammed shaft which moves both rotationally and linearly as the chuck block is raised and lowered by the lifting arm. The cam shaft has a plurality of yoke cam grooves which engage a biased cam follower in the table member whereby the cam follower follows a reversing cam path defined by the plurality of yokes, each yoke forming a pair of angular grooves in the configuration of a Y, a portion of each yoke being common to its adjoining yoke so that adjoining Y configurations are alternately reversed. Each yoke is defined by an upper pair of aligned rest stops and an intermediate lowered reverse stop, the cam follower imparting rotation to the chuck block as it moves in transit from one rest stop to the adjoining rest stop.