Abstract: A sintered vitrified superfinishing grindstone is provided which is a sintered product which is obtained by compression molding of a mixed powder of: a sinterable vitrified binder composed of a powder of a borosilicate glass composition; hard abrasive grains; and soft abrasive grains; and which includes bonded portions formed by necking due to heat compression, between particles of the powder of the borosilicate glass composition which are in contact with each other; and wherein the sinterable vitrified binder contains from 94 to 100% by mass of a powder composed of a low-melting-point borosilicate glass composition containing from 35 to 55% by mole of SiO2; from 3 to 5% by mole of Al2O3; from 10 to 35% by mole of B2O3; and from 25 to 30% by mole of R2O+RO.

Abstract: A machining apparatus includes a transfer mechanism portion and a grinding wheel unit. The transfer mechanism portion transfers a tapered roller having a large end face directed outward in a radial direction by causing the tapered roller to revolve about a vertical line while causing the tapered roller to rotate. The grinding wheel unit is substantially C-shaped, and has a grinding wheel surface that comes in sliding contact with the large end face of the transferred tapered roller on an inner peripheral side thereof. The grinding wheel unit has a substantially C-shaped seat fixed to an apparatus main body, and a grinding wheel body that is separate from the seat and is detachably mounted to the seat. The grinding wheel body is substantially C-shaped, and has the grinding wheel surface on an inner peripheral side thereof. The grinding wheel body is constituted by segments disposed along a circumferential direction.