Annular glass substrate, method for producing annular glass substrate, method for producing annular glass substrate, and method for producing glass substrate for magnetic disk

摘要

A process for forming an annular glass blank from a plate-shaped glass blank, wherein on a main surface of the plate-shaped glass blank: a first circular blade is turned along the main surface at a first turning radius to form an outside incision; and a second circular blade is turned along the main surface at a second turning radius that is smaller than the first turning radius to form an inside incision. A plurality of first cutouts are provided to the cutting edge of the first circular blade so as to be set apart from each other in the circumferential direction by a first spacing, and a plurality of second cutouts are provided to the cutting edge of the second circular blade so as to be set apart from each other in the circumferential direction by a second spacing. The first spacing is smaller than the second spacing. The concentricity between the inner peripheral end surface and the outer peripheral end surface of the annular glass blank is 15 μm or less. The difference between the roundness of the outer peripheral profile of a first main surface of the annular glass blank and the roundness of the outer peripheral profile of a second main surface, which is located on the reverse side from the first main surface, is 100 μm or less.