Manufacturing method of a sheet glass material for magnetic disk and manufacturing method of a glass substrate for magnetic disk

A manufacturing method of a glass substrate for magnetic disk, the method including:

• dropping process for dropping a lump of molten glass;
• pressing process for sandwiching simultaneously the lump from both sides of the dropping path of the lump with surfaces of a pair of dies facing together, and performing press forming to the lump to obtain a sheet glass material;
• and
• machining process for machining the obtained sheet glass material,
• wherein at least one of the pair of dies has a convex shape with respect to the dropping path of the lump, and
• wherein the machining process includes grinding process for grinding the principal surfaces using fixed abrasive grains, and polishing process for polishing the principal surfaces using loose abrasive grains after the grinding process.