A device for limiting the advance during a drilling operation includes, for example, a cylindrical housing with a rotatably mounted spindle arranged coaxially therein with a drive-side end and a tool-side end, which has limited displaceability in the axial direction. The drive-side end of the spindle is designed in such a way that it can be clamped into a drill chuck of a hand drill or into a corresponding receiver of an automatic manufacturing machine. The tool-side end of the spindle is provided with an internal thread, into which an appropriate drilling tool can be screwed. What are known as stepped drill bits, which combine a drill bit and a countersink, are used as the drilling tool in conjunction with devices of the said kind. The drilling tool is surrounded by a stop cage, fixed to the housing, with lateral openings, which is brought to bear against a workpiece at the beginning of the drilling operation. Chips produced during drilling are intended to leave the stop cage through the lateral openings. To limit the drill advance in the direction towards the workpiece, an adjustable stop is provided inside the housing. Such devices are used in order to ensure reproducible countersinking depths in the production of bores with a countersunk recess. In this connection, on the one hand, too deep a countersunk recess may lead to rejects and, on the other hand, a countersunk recess with too small a depth makes complicated refinishing necessary.
It is a disadvantage of devices of the abovementioned kind that the chips produced lead to undesirable secondary effects depending on the material to be machined if the workpieces concerned have a sensitive surface. This undesirable effect consists in that, in particular during drilling of the countersunk recess, flowing chips are produced, which wind themselves around the tool and in this way give rise to coiled chips or chip coils. In this connection, the chip coils are whirled around the drilling tool, so that the rotating flowing chip wound around the drilling tool carries out uncontrolled movements and in doing so damages the surface of the workpiece to a greater or lesser extent by scratching. Removal of the scratches produced in this way requires a considerable degree of extra work. In addition, the operating sequence is disrupted by virtue of the chip coils having to be removed by hand after each drilling cycle.
USPTO Backgrounds
USPTO Backgrounds