| 摘要 |
In apparatus for drilling a hole in the ground comprising tubing for shoring up the walls of the drilled hole and a drilling member comprising a pneumatic percussion hammer having an eccentric cutting edge, the drilling member extending in the tubing and having a working position in which the cutting edge extends below the lower end of the tubing and a removal position in which the cutting edge is within the tubing, the extension tube for supplying gas to the hammer is connected to the hammer by a helicoidal telescopic connection which is rotatable through 180 DEG between retracted and extended positions, a decentring spline being mounted on that part of the telescopic connection connected to the extension tube and arranged so that, in the retracted position of the telescopic connection, assumed when the drilling member is in its working position, the cutting edge is diametrically opposite the spline and, in the extended position of the telescopic connection, assumed when the drilling member is in its removal position, the cutting edge is aligned with the spline. |
