| 摘要 |
PROBLEM TO BE SOLVED: To effectively use a lead becoming shorter, and at the same time, prevent the lead from breaking by making the radius of curvature of the lead gripping section of a chuck equivalent to ore slightly larger than the radius of the lead to be used. SOLUTION: A second chuck body 7 which projects from the tip end of a forward member and is detachably fixed to the tip end of a barrel cylinder, is divided into three, and chuck pieces 7a, 7b and 7c are formed, and the radius of curvature RI of a gripping section 10 which grips/release a lead L is formed to be equivalent to or slightly larger than the radius R2 of the lead L to be used. By this constitution, compared to a conventional technique wherein the lead is held by linear corner sections, the lead L can be held by contact surfaces in the circumferential directions and the longitudinal sections of respective gripping sections 10, and at the same time, by an extremely slight arc-form chamfer process which is applied on the internal surfaces of the tip ends of the gripping sections 10, the lead L can be prevented from breaking.
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