| 摘要 |
PROBLEM TO BE SOLVED: To produce the form rolled ball screw having a prescribed lead precision by providing a column part, of which the diameter is larger than a thread groove root diameter and smaller than a stock bar diameter and a tapered part continuing to the column part and spreading to a stock diameter side, at a stock bar end part into which a roll die bites so that a stock bar is normally bitten into a roll die. SOLUTION: A column part 2 having diameter A and length L is formed at the end part of a stock bar 1. Diameter A=(stock bar diameter D + thread groove root diameter F)/2 and length L=(roll die width)×2/3 are defined. A tapered part 3, which spreads at a tapered angleθ1 between the column part 2 and a stock bar diameter D side, is formed. The tapered angleθ1 is 1-3 deg.. A chamfered part 4 is formed at the edge of the column part 2 so that the stock bar 1 is easily bitten into a roll die. When form rolling a stock having a screw nominal external diameter exceeding 60 mm, the roll die does not idly run not to cause burning, form rolling force is not required to increase more than a normal value.
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