| 摘要 |
The drilling apparatus for making a drilled hole with an undercut includes a drive device for rotating a hollow drilling shaft (3); a drill bit holder (23,38) held in the hollow drilling shaft (3); a drill bit (4,26) having a drilling head provided with laterally projecting cutting edges (25) projecting from the drill bit holder (23,38); a device for swivelling out the drill bit holder (23, 38) with the drill bit from a drilling center line (5) including at least one control element of the drill bit holder, a sliding sleeve (11) surrounding the drilling shaft (3) and a swivelling-out element (21,39) connected to the movable sliding sleeve and engaging the control element to swivel out the drill bit holder (23, 38); and a device for raising and lowering the drive device (2) together with the drill bit holder (23,38) and the drill bit (4,26). In one embodiment the swivelling-out element is a sliding block and the control element is a cam surface in a slot provided in the drill bit holder.
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