a double - head drilling machine is disclosed , which by changing over or converting small component units can cooperate with drill or drill pipes of different diameters . to this end , drive carriages operating on drills or drill pipes , for example , comprise a carriage base element , to which a drive unit is releasably fitted . the drive unit can thus be replaced by a different drive unit having essentially the same geometry , which is designed for operating with a drill or drill pipe having a different diameter .