In order to carry out a core drilling operation, a drill bit connected to a core drill is usually positioned on the surface of a mineral material to be worked. For this purpose, a water supply system, which is used for rinsing and cooling the drill bit during the core drilling operation, is switched on and the core drill transfers a torque to the drill bit, whereby the drill bit is set into a rotary motion. With the aid of the transferred torque, the cutting segments (also referred to as teeth) mounted on the lower end of the drill bit cut a hole into the mineral material.
Certain problems may arise at the beginning of the core drilling operation, however, if the drill bit is set down in an uncontrolled manner and too quickly on the surface of the mineral material to be worked. This may result, for example, in a twisting of the entire core drilling system, i.e., the unit made up of the drill bit, the core drill, and the machine holding device. Such a twisting causes unintentional torsional forces to act with increased mechanical loads on the entire core drilling system and, in particular, on the unit made up of the core drill including the drill bit. In addition, the twisting causes the drill bit to be set down onto the surface of the mineral material in an imprecise, i.e., non-planar manner, which may result in inaccuracies in the determination of the drilling depth. The unintentional twisting is further intensified, in particular, by the use of spacers between the machine holding device and the core drill including very large drill bits.
The problem of unintentional twisting is solved in the case of core drills according to the prior art, which include conventional control methods, in that, if the drill bit is set down onto the surface of the mineral material too quickly, the drill bit, along with the core drill, is removed from the surface with the aid of the feed device in order to remove the mechanical load or tension from the core drilling system. As a consequence of once more lifting and suddenly relieving the drill bit and the core drill, however, the core drilling system perceives this as a greatly reduced resistance at the drill bit and, as a result, the feed device reacts with a rapid advance. Consequently, the drill bit impacts the surface of the mineral material at a speed which is too high. As a result, the individual cutting segments, the drill bit, and/or the core drill may become damaged. When the core drilling system detects that the drill bit has been set down onto the surface of the mineral material too rapidly and too hard, the drill bit, along with the core drill, is removed again from the surface with the aid of the feed device. The above-described procedure then starts over again. An unintentional start-up of the control method takes place.