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

In the process of forming an annular glass base plate from a plate-like glass base plate, the first circular blade is rotated at a first turning radius along the main surface with respect to the main surface of the plate-like glass base plate. An outer cut line is formed, and the second circular blade is rotated along the main surface with a second turning radius shorter than the first turning radius to form the inner cut line. A plurality of first cutouts are provided on the cutting edge of the first circular blade at a first interval in the circumferential direction, and a plurality of second cutouts are provided on the cutting edge of the second circular blade. Are provided at a second interval in the circumferential direction. The first interval is smaller than the second interval. The concentricity between the inner peripheral end face and the outer peripheral end face of the annular glass base plate is 15 μm or less. The difference between the roundness of the outer peripheral shape of the first main surface of the annular glass base plate and the roundness of the outer peripheral shape of the second main surface opposite to the first main surface is 100 μm or less. is there.