Abstract: A drill bit for use in a drill string comprising a set of a plurality of central rod members and a set of a plurality of tubular members surrounding said rod members. The drill bit is provided with a longitudinally extending flushing channel which communicates with an annular space between the rod members and the tubular members via a transverse passage. The flushing channel comprises at least two end passages terminating in the bit front. The cross section area of each of the end passages is smaller than the overall cross section area of the portion of the flushing channel located between the end passages and the transverse passage.

Abstract: The invention relates to a drill element for percussion drilling, the element having a cylindrical screw thread having one single entry. The screw thread, that is intended for thread diameters of less than 30 mm, has a pitch of less than 12 mm, a shoulder angle of less than 69.degree., and a pitch angle of less than 11.degree. but more than 5.6.degree..

Abstract: A rock drill bit of the impact type comprising a boring head, a shaft having ridges, a front surface and a number of peripherally spaced holes receiving inserts, said holes extending forwardly and outwardly at an acute angle .phi. with respect to the center line of the drill bit. The guiding surface of the insert mainly coincides with the jacket surface of the bit body when the insert has been fixed in the hole which emerges into both the jacket surface and the front surface of the bit body. This means that the guiding surface partly extends on both sides of the plane of the front surface.

Abstract: A guiding means in rock drilling for guiding a percussion drill string (10) comprises a guide sleeve (17). For purposes of ensuring free rotation between the drill string (10) and the guide sleeve (17) the latter is bound by shape to the drill string at its one end during drilling as well as during withdrawal of the drill string (10).

Abstract: A boring head for reaming a pre-drilled hole in raise boring or for similar earth cutting operations comprising a plurality of roller cutters (13, 14), each of which being rotatably journalled over a bearing system. The bearing system comprises a split roller bearing (60) having axially spaced rollers (62, 63) which are separated by a loose guide ring (69).

Abstract: A bore head for reaming a pre-drilled hole in raise boring or for similar earth cutting operations comprising at least two sets of roller cutters. The roller cutters in the same set of cutters have the same number of rows of cutting means. The roller cutters are mounted in pairs on each side of the rotational axis of the bore head. During rotation of the bore head the cutting means move along concentric circles. In order to change the distance between two consecutive circles a roller cutter in one of the pairs of cutters is replaced by a roller cutter of the other set of cutters.

Abstract: A reamer bit for raise boring in rock, of the type comprising a body on which a number of rolling cutters with cutting inserts are rotatably mounted for contact with and disintegration of the rock, and a detachable stem mounted in a central bore on the body and adapted to be received in a pilot hole drilled in advance in the rock. The stem has two cylindrical portions, an upper one of which having a smaller diameter than a lower one thereof. The bore in the body has corresponding upper and lower cylindrical portions surrounding the stem. The upper cylindrical portions of the body and the stem define upper stem restraining surface means. The lower cylindrical portions of the body and the stem define lower stem restraining surface means. The stem at its lower portion is provided with a flange abutting the body from below and supporting it axially. The upper and lower restraining surface means together comprise a substantial axial portion of the part of the stem that is surrounded by the bore.