A cover assembly for a machine tool having a base supporting a workhead and a second machine part such as a spindle housing, headstock or tool turret, and wherein a rotatable workpiece changing mechanism is provided in conjunction with the workhead. The cover assembly includes an external housing member which encloses the workhead and the second machine part and permits movement of the second machine part therewithin. The external housing member further includes a workpiece exchange opening and a workpiece exchange shield which is reciprocable between a first position which effectively closes the opening, and a second position which allows unencumbered rotation of the workpiece changing mechanism. The shield is reciprocable in parallel with the workpiece changing mechanism to obviate added machine idle time. An internal housing substantially encloses the second machine part within the external housing, and is mounted for movement with the second machine part. The cover assembly accommodates varying machine tool configurations with only minimal changes of relatively modular parts.