Sleeper drilling machines
The forces acting on the rail fastenings produce tensile and shear stresses. These must be transferred to wooden sleepers by means of the screw hole in the sleeper. Therefore, it is not surprising that with particularly high loads (e.g. in curves or turnouts) the friction bond between the fastening screw and wooden sleepers can fail. This failure has a major effect on the error in the track gauge and on the safe operation of the track.
During upgrading and conservation work on wooden sleepers the plates required to secure the rails must be readjusted. During this process, the existing screw holes in the wooden sleepers are refurbished and accurately re-drilled with special machines.