A cutter holder has a body and a buffering assembly. The body has a specific weight. The buffering assembly is mounted in the body and has a buffering unit and an elastic unit set. The buffering unit has a specific weight that is larger than the specific weight of the body. The buffering unit and the elastic unit set are utilized for absorbing vibration. The elastic unit set has multiple Belleville washers and can be changed in scales or amounts according to practical machining conditions.

A drill reamer (20) comprises an elongate body (21) disposed about a longitudinal axis. The elongate body comprises flutes (22a-22d) having separate hard cutting sections (27a, 28a, 28a, 28b, 28b) and a soft cutting section (24a, 24b). The soft cutting section is formed of a material such as carbide having a hardness that is less than that of the hard cutting sections, which may be formed of polycrystalline diamond. At least one first hard cutting section (27a) is axially displaced relative to at least one second hard cutting section (28a, 28a). The reamer has a tip cutting edge (23a, 23c) and tapered cutting edge portions (24a-24d) disposed at an acute angle relative to the longitudinal axis.

cBN sintered material, including cBN particles; a binder phase; and a first phase, wherein the content of the cBN particles in the cBN sintered material is 25% to 80% by volume, the binder phase contains either or both of one or more first compounds, and a solid solution derived from the first compound, the first phase contains cobalt, tungsten, and at least one first element selected from the group consisting of the elements contained in the binder phase, the total content of cobalt and tungsten in the cBN sintered material is 1.0% to 6.0% by mass, the binder phase consists of multiple binder phase particles containing 50% or more of first binder phase particles on a number basis, surfaces of the first binder phase particles include 50% by area or more of a first region which is in contact with the first phase.

A cemented carbide includes 65 to 85 volume % of a first phase and 4 to 25 volume % of a second phase, wherein the first phase consists of carbide grains, the second phase includes 50 mass % or more of cobalt, the second phase includes zirconium, a cobalt content ratio M.sub.Co of the cemented carbide is 3 to 15 mass %, a and b of the cemented carbide indicate a relation of the following formula I:
b<0.0485a+0.0001I, where
a represents a percentage, (M.sub.Zr/M.sub.Co)100, of a zirconium content ratio M.sub.Zr in mass % with respect to the cobalt content ratio M.sub.Co in mass %, a is more than 0 and 8 or less, b represents an area percentage of pore in a first region of the cemented carbide, and the first region is a region located within a distance of 50 m from a surface of the cemented carbide in the cross section.

cBN sintered material, including cBN particles; a binder phase; and a first phase, wherein the content of the cBN particles in the cBN sintered material is 25% to 80% by volume, the binder phase contains either or both of one or more first compounds, and a solid solution derived from the first compound, the first phase contains cobalt, tungsten, and at least one first element selected from the group consisting of the elements contained in the binder phase, the total content of cobalt and tungsten in the cBN sintered material is 1.0% to 6.0% by mass, the binder phase consists of multiple binder phase particles containing 50% or more of first binder phase particles on a number basis, surfaces of the first binder phase particles include 50% by area or more of a first region which is in contact with the first phase.

A diamond cutting tool comprises a base metal part and a diamond part joined to the base metal part, wherein the base metal part is made of an alloy containing tungsten carbide, the diamond part configures at least a cutting blade, the cutting blade comprises a portion of a rake face, a portion of a flank face, and a ridge line at which the rake face and the flank face cross, the diamond cutting tool has a region A, the region A is a region that is present bridging over the three, which are the rake face, the ridge line, and the flank face on the surface of the cutting blade, and the region A has a surface roughness Ra of not more than 0.2 m and a concentration of tungsten element of not more than 1 mass %.