| 摘要 |
PROBLEM TO BE SOLVED: To secure a sufficient gap between a magnetic sheet and an upper edge and to prevent a recording surface from being damaged by proving a flank of a specified clearance angle at an edge part. SOLUTION: In an upper edge K1, a first knife K1 is pressed on a first spacer 5 having an angleθ3 larger than a bevel angleθ2 of the first knife K1 by 10 to 50 by a second spacer 7 having the same angleθ3 as that of the first spacer 5 by using a jig at the time of polishing, the bevel angleθ2 is increased by 1 deg. to 50 and an outer peripheral side K1b is polished. When the first spacer 5 and the second spacer 7 are removed after polishing, the original bevel angleθ2 is restored from elasticity that the upper edge K1 has. At the same time as this restoration, a flank of 1 deg. to 5 deg. is formed by a clearance angleθ1. Thus, a sufficient gap between a magnetic sheet and the upper edge K1 can be secured and as a result, recording surface can be prevented from being damaged.
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