| 摘要 |
A device for drilling an undercut in a borehole in a receiving material comprises an axially extending guide sleeve with an eccentric bore and an eccentric bushing located in the eccentric bore and being rotatable therein relative to the sleeve. A tension spring is located between the sleeve and the bushing. During rotation of the bushing, relative to the sleeve, the torsion spring is stressed. A drive shaft with a cutter head at one end extends through the bushing and is brought into an eccentric position relative to the sleeve and at the same time commences an undercut in the borehole. A lock is provided with a set of teeth on the sleeve preventing rotation of the sleeve with the bushing. When the maximum eccentricity of the drive shaft is established, the lock can be released and the sleeve rotated along with the bushing by an eccentric transmission. During such rotation, a complete circumferentially extending undercut can be formed in the borehole. After completing the undercut, the torsion spring can rotate the sleeve relative to the bushing for returning the drive shaft to a centered position within the sleeve.
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