ROTARY TOOL,TOOL ASSEMBLY AND PROCESS

1418944 Mineral-mining, rotary cutter tools VEREINIGTE OSTERREICHISCHE EISEN-UND STAHLWERKE-ALPINE MONTAN AG 29 June 1973 [30 June 1972] 31052/ 73 Heading E1F The bit arrangement of a mineral-mining rotary cutter tool, which is mounted for rotation about an axis parallel to a face being cut by the tool and simultaneous feed along said axis with the ratio between the volocities of rotation and feed of the tool being maintained constant, is such that the bits are arranged in sets of equal numbers in axially spaced planes, the bits of each set are on a common circumference, the circumferences of the sets diminish axially towards the foreward end of the tool, the bits of successive sets are spirally arranged relative to one another whereby when the above referred to ratio is maintained constant the bits of the larger diameter set will follow into the same grooves as cut by the adjacent smaller diameter set, and the cutting faces of the bits are arranged normal to their paths of displacement resultant from said ratio of velocities. Preferably the product of the width of the cutting faces of the cutter bit of a set and the number of bits in the set does not exceed the axial displacement of the tool during one revolution thereof. Also the axial distance between the bits of two adjacent sets may be equal to the product of the tangent of the angle of inclination of the bits of the larger diameter set and the length of arc described by the end of said bits over the angle by which said bits lay behind the bits of the smaller diameter set which respectively precede said bits in the grooves being cut.