Abstract: A tire building drum is described as having a unique mechanism for controlling the radial movement of the bead lock segments which are designed to hold the tire bead rings firmly, in position, during the tune-up operation. The mechanism includes an annular support member which is disposed concentrically around the longitudinal center axis of the drum adjacent opposing ends of the drum, and which has a number of raceways that are radially oriented in relation to said center axis. The raceways are equally, angularly spaced about said axis and are designed to slidably receive a bead lock segment on which a cam roller is freely mounted for rotation. The mechanism also includes an annular scroll member which is disposed concentrically around said axis in side-by-side parallel relation with each of the support members.