Thread-Rolling Machine, Automatic

a machine designed to cold-work external screw thread on solid cylindrical blanks. An automatic thread-rolling machine usually has two thread rolls with screw threading that corresponds to the profile of the thread to be rolled. During the rolling process, the rolls turn in the same direction at the same frequency. The blank is mounted between the rolls on a rest. One roll is advanced in a radial direction until the blank is penetrated to the desired depth, which corresponds to the thread profile; the thread is then calibrated (rolling without radial feed). The roll returns to the starting position upon completion of the rolling step, and the finished part is expelled into the receiving bin. The difference in the average roll diameters must not exceed 0.03–0.05 mm in order to avoid slippage of the blank and distortion of the profile. In some automatic thread-rolling machines, the thread is formed by flat screw-threading dies.