Abstract: An annular grinding stone is provided which includes a cutting edge with a plurality of V-shaped slits defined in an outer circumferential portion thereof is provided. Each of the V-shaped slits is defined by a first surface and a second surface of the annular cutting edge. The first surface is positioned rearwardly of the second surface with respect to a direction along which the annular grinding stone rotates, and the second surface is positioned forwardly of the first surface with respect to the direction along which the annular grinding stone rotates. The first surface lies perpendicularly to the direction along which the annular grinding stone rotates at a radially outer end thereof and parallel to thicknesswise directions of the annular cutting edge. The second surface is inclined with respect to the first surface at an angle ranging from 30° to 60°.

Abstract: An annular grinding stone is provided which includes a cutting edge with a plurality of V-shaped slits defined in an outer circumferential portion thereof is provided. Each of the V-shaped slits is defined by a first surface and a second surface of the annular cutting edge. The first surface is positioned rearwardly of the second surface with respect to a direction along which the annular grinding stone rotates, and the second surface is positioned forwardly of the first surface with respect to the direction along which the annular grinding stone rotates. The first surface lies perpendicularly to the direction along which the annular grinding stone rotates at a radially outer end thereof and parallel to thicknesswise directions of the annular cutting edge. The second surface is inclined with respect to the first surface at an angle ranging from 30° to 60°.

Abstract: An automatic tool changer includes a main spindle having a bore inside, a chuck provided at an opening of the main spindle, a plurality of tools accommodated in the bore of the main spindle, wherein the tools are individually slidable axially of the main spindle, means for pushing the tools toward the opening of the main spindle, thereby replacing a first tool on the chuck with a second tool accommodated in the bore of the main spindle.