Porasovitelma

Drill assembly for making a hole into a soil or rock which arrangement comprises a pilot bit (10) drilling the middle part of the hole and a ring bit (1) drilling the outer circle of the hole in which case in the drilling situation the ring bit (1) is adjusted around the pilot bit (10) and rotary movement and drilling impacts are directed from the pilot bit (10) to the ring bit (1) with the help of the mentioned surfaces (4-6);(7-9),(15, 16) adjusted between the bits and conveying power and that the ring bit (1) can be removed around the pilot bit (10) and can be installed to it and that further a coupling ring (2) belongs around the ring bit (1) in order to join a casing pipe, which can be pulled to the drilled hole, to the ring bit (1) with the help of the mentioned coupling ring. The coupling ring. (2) is adjusted around the periphery of the ring bit (1) in such a way that of the parts (13) taking part in the locking of the coupling ring (2) at least two are located at the different sides of the line (L) when the arrangement is assembled which line runs essentially through the middle point of the surface (5) conveying the rotation of the ring bit (1).