Method for manufacturing annular glass substrate, annular glass substrate, and method for manufacturing glass substrate for magnetic disc

An annular glass substrate comprising:

• two main surfaces;
• an outer circumferential edge surface that connects outer edges of the two main surfaces;
• an inner circumferential edge surface that is concentric with the outer circumferential edge surface and is formed inside the outer circumferential edge surface,
• wherein the outer circumferential edge surface includes a first region and a second region,
• each of the first region and the second region is formed with a plurality of grooves extending in a thickness direction of the disc-shaped or annular glass substrate,
• in the first region, the grooves are periodically formed and an interval between a pair of adjacent grooves is a first interval,
• in the second region, an interval between a pair of adjacent grooves is shorter than the first interval,
• the inner circumferential edge surface is provided with a plurality of grooves extending in the thickness direction of the annular glass substrate, a third region, and a fourth region,
• in the third region, the grooves are periodically formed and an interval between a pair of adjacent grooves is a second interval, and
• in the fourth region, an interval between a pair of adjacent grooves is shorter than the second interval.

An annular glass substrate comprising:

• two main surfaces;
• an outer circumferential edge surface that connects outer edges of the two main surfaces;
• and
• an inner circumferential edge surface that is concentric with the outer circumferential edge surface, is formed inside the outer circumferential edge surface, and connects inner edges of the two main surfaces,
• wherein the inner circumferential edge surface includes a third region and a fourth region,
• each of the third region and the fourth region is formed with a plurality of grooves extending in a thickness direction of the annular glass substrate,
• in the third region, the grooves are periodically formed and an interval between a pair of adjacent grooves is a second interval, and
• in the fourth region, an interval between a pair of adjacent grooves is shorter than the second interval.