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| The threaded faces of hardened steel dies are pressed against a
cylindrical blank to reform the surface into threads. The dies displace the material
to form the roots of the thread and force the displaced material outward to form the
crests. |
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As the table indicates, only a thread produced by the very expensive
grinding technique, can even approach a rolled thread in the surface smoothness
department. In any cold forging process, the finished product's surface very closely
resembles the surface of the dies. Thread rolling dies are ground and polished to
perfection. Reforming material with a highly polished die produces a smoother finish
than removing material with a cutting tool. |
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| These diagrams indicate a rolled thread's superior resistance to
stripping. The rolled thread's grain structure is not severed in any way, but is,
instead, reformed in unbroken lines that follow the thread's contours. Therefore,
for a shear failure to take place, it must occur across, rather than with the grain. |
