| 摘要 |
PROBLEM TO BE SOLVED: To prolong durability of a tooth form assembly and a core bar which is a jig for form rolling for the tooth form used in form rolling of a hollow rack bar out of a pipe. SOLUTION: A tooth form assembly body 12 used in form rolling of a hollow rack bar out of a hollow pipe is equipped with a tooth form 26 and a tooth form holder 22. The tooth form 26 is removably inserted in a recess 24 formed in the tooth form holder and provided with press-in pieces 28, 30 longitudinally urging the tooth form 26 in the recess 24 of the tooth form holder, and further, pin holes 32, 34 for extruding the press-in pieces are opened at the bottom face of the recess opposite to the press-in pieces. The core bar 20 is provided with a plurality of expanded heads 20B. The expanded head 20B forms a slope face that the ratio of the length to the overhanging length is specified at the forward port.
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