Method for preparing a glass spacer ring for a magnetic disk and spacer ring

摘要

A glass spacer ring is prepared into a round slice from a glass tube having an outer diameter and a wall thickness corresponding to an outer diameter and a width of the spacer ring, respectively, by engraving a cutting line 7 on an inner side of a glass tube with a cutter in a direction perpendicular to a tubular axis thereof at a cutting interval corresponding to the thickness of a space ring, and heating the cutting line 7 with a burner from an outer side of the glass tube to cut the glass tube by heat shock.