Abstract: An apparatus positions a rotary drum having an axis of rotation in an image scanner having a frame to position an image source mounted on the rotary drum. A way is mounted to the frame. A headstock and a tailstock are disposed and arranged to receive and support the rotary drum and are independently mounted on the way for lineal movement along the axis of the drum. A drum drive device rotates the drum about the axis and a headstock drive device linearly moves the headstock along the axis in first and second opposite directions. A stop block is supported by the frame and impedes a linear movement of the tailstock in the second direction at a selected stop position.