Patent ID: 8869559

Claim:
A method for manufacturing sheet glass material for a magnetic disk including a pair of principal surfaces, the method comprising: performing a dropping process to drop a lump of molten glass in vertically downward direction, the lump being made by cutting molten glass; performing a forming process, after beginning the dropping process, to form the sheet glass material by sandwiching substantially simultaneously the lump of molten glass from both sides of a dropping path of the lump with inner surfaces of a pair of dies at a timing as the lump is dropping and when a portion including a cut mark of the lump protrudes from the pair of dies facing together, to press form the lump of molten glass into the sheet glass material; and removing the portion of the sheet glass material protruding from the pair of dies while the dies are sandwiching the lump; the molten glass being cut in the dropping process such that the lump of molten glass is shorter in a parallel direction to the inner surfaces of the pair of dies than the sheet glass material is after being formed; and the lump of molten glass being pressed during the forming process to extend along the inner surfaces of the pair of dies such that the principal surfaces of the sheet glass material have a flatness of 4 μm or less after the removing.