Importance

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Abstract

A drilling tool for percussive and rotary drilling in advance of a trailing casing tube (20) has a reamer (15) pivotally journalled and an eccentric shaft (12) rearwardly of a centric pilot bit (11). The reamer (15) has an eccentric portion (32) carrying axially directed hard metal button inserts (36-40) grouped within an arcuate angle (V) of a circle sector centered on the drilling axis (C). The inserts comprise primary inserts (36-38) with a radial reach defining the full diameter of the drilled hole and inner secondary inserts (39, 40) closer to the shaft (12). The reamer (15) is pivotable on the shaft (12) between a projected and a retracted position. When projected, the group of button inserts (36-40) ream up the hole from the diameter drilled by the pilot bit (11) to the full diameter of the hole enabling the casing tube (20) to advance. In the retracted position, the drilling tool (10) can pass through the casing tube (20). A duality of inserts (36, 39) leading in the rotational direction act jointly to break rock in a direction substantially tangentially relative to the shaft (12).

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First Claim