Method for producing glass substrate for magnetic disk and method for producing magnetic disk

A method for producing a glass substrate for a magnetic disk, comprising:

• measuring each surface waviness of one surface and an other surface opposite to the one surface to select, as a selected surface, the one surface which is small in surface waviness relative to the other surface;
• forming a cut line in the selected surface;
• extending the cut line in a thickness direction of the glass material;
• and
• cutting the glass material into the glass substrate;
• wherein a circle with a radius of 10 mm or less is cut out by forming the cut line in the selected surface.

A method for producing a glass substrate for a magnetic disk comprising:

• forming a cut line in one surface of a planar glass material so as to draw a circle extending along a substantial periphery of a region in which a glass substrate for a magnetic disk is to be formed;
• allowing the cut line to extend in a thickness direction of the glass material, thereby cutting a disk-shaped glass plate;
• and
• making the glass substrate for the magnetic disk from the cut glass plate,
• wherein, when the circle, which has a radius not greater than 10 mm, is cut out by forming the cut line, a maximum height of surface waviness of the glass material is measured on the one surface, the one surface of the glass material having a predetermined maximum height of surface waviness is selected, and then the circle is cut out;
• wherein a glass material satisfying a relationship PV≦5×r is selected, wherein r [nm] is a radius of the circle, and PV [nm] is the maximum height of surface waviness;
• and
• wherein the surface waviness of the one surface falls within a waviness wavelength band between 0.1 mm and 5 mm.

A method for producing a glass substrate for a magnetic disk comprising forming a cut line in one surface of a planar glass material so as to draw a closed curve extending along a substantial periphery of a region in which a glass substrate for a magnetic disk is to be formed;

• allowing the cut line to extend in the thickness direction of the glass material, thereby cutting a disk-shaped glass plate;
• and making the glass substrate for the magnetic disk from the cut glass plate,
• wherein cutting is performed under the conditions where the thickness (t [mm]) of the glass material and the maximum height of surface waviness (PV [nm]) of the glass material satisfy a predetermined relationship;
• wherein the predetermined relationship is PV≦50t;
• wherein the surface waviness of the one surface falls within a waviness wavelength band between 0.1 mm and 5 mm;
• and
• wherein the thickness of the glass material is not thicker than 1.5 mm.

A method for producing a glass substrate for a magnetic disk comprising forming a cut line in one surface of a planar glass material so as to draw a curve extending along a substantial periphery of a region in which a glass substrate for a magnetic disk is to be formed;

• allowing the cut line to extend in the thickness direction of the glass material, thereby cutting a disk-shaped glass plate;
• and making the glass substrate for the magnetic disk from the cut glass plate,
• comprising:
• measuring a surface waviness on two opposing surfaces of the glass material which has a thickness of 1 mm or less;
• and
• selecting, as a selected surface, the one of the surfaces which is small in the surface waviness as compared with the other surface;
• wherein, when the disk-shaped glass plate is cut from the glass material, the cut line is formed in the selected surface.

A method for producing a glass substrate for a magnetic disk comprising forming a cut line in one surface of a planar glass material so as to draw a curve extending along a substantial periphery of a region in which a glass substrate for a magnetic disk is to be formed;

• allowing the cut line to extend in the thickness direction of the glass material, thereby cutting a glass plate;
• and making the glass substrate for the magnetic disk from the cut glass plate,
• wherein, when the planar glass material with a predetermined thickness is cut, a maximum height of surface waviness of the glass material is measured on the one surface of the planar glass material, the measured glass material having a predetermined maximum height of surface waviness on the one surface is selected, and then the cut line is formed in the one surface of the planar glass material;
• and
• wherein the one surface of the measured planar glass material satisfying a relationship PV≦50t is selected, wherein t [mm] is the thickness, and PV [nm] is the maximum height of surface waviness;
• wherein the surface waviness of the one surface falls within a waviness wavelength band between 0.1 mm and 5 mm;
• and
• wherein the thickness of the glass material is not thicker than 1.5 mm.