Process and apparatus for operating an apparatus to drill holes in the shell of a paper machine cylinder. The apparatus includes a stationary framework supportable on the paper machine, a feed frame that is radially movable along the stationary framework relative to the shell, and a drive unit. A plurality of drilling modules are coupled to the feed frame, which are rotatable via the drive unit, and the drilling modules include a drive shaft, at least two spindle heads, and at least two intermediate shafts arranged between the drive shaft and the at least two spindle heads, in which at least one of the at least two spindle heads in each drilling module is rotatable about a respective intermediate shaft of the drilling modules. The process includes rotating at least one of the at least two spindle heads about a respective intermediate shaft of the drilling module arranged between a drive shaft and the at least one spindle head, such that a mutual distance between spindle shaft centers of the at least two spindle heads in the drilling modules is adjusted.