The regenerative chatter in thread turning of steel solid bar occurs due to rocking-bending mode of the lathe spindle. In thread turning of circular tube with thick chucking part, the chatter occurs due to vibration by radial deformation mode of the tubular work. Spindle bending and tubular work deformation are two possible modes of vibration in thread turning of straight steel tube. For suppressing regenerative chatter in thread turning, alternating variation of spindle speed is found to be

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... ective by this study. A control program which synchronizes rotational angle of the main spindle and the longitudinal feed motion of the tool with an invariable phase difference, has been developed. Also a canned cycle that controls speed variation range, cross section area of cutting and other working parameters, has been developed for thread turning. Those new developments are effective in suppressing the chatter in screw thread turning of steel solid bar and steel tube.