Investigation of the influence of the cutter-tool rake angle on the accuracy of the conical helix in the tapered thread machining

Abstract

Abstract Tapered thread joints used in drill pipes largely determine the productivity of drilling processes and their environmental reliability. The quality of these joints depends on the values of the rake angle of the cutting insert of turning cutters used for making tapered threads. Modern manufacturers, because of the absents of algorithms for calculating the precision of the execution of the tapered thread spiral, depending on the size of the rake angle use the cutters only with a zero value of this angle. This greatly limits the possibility of producing drill pipes from high-strength materials, which is absolutely necessary in the modern drilling methods: obliquely directional and horizontal. The kinematic analysis presented in the article proves the difference between the theoretically specified spiral and their realized in the course of machine processing with cut tools with non-zero values of the rake angle. The deviation of the thread incline angle that is realized during turning is not regulated by standard requirement, as it is variable. The precision of the pitch of the tool-joint tapered thread is regulated by standard and must be ensured by the kinematics of the lathe. However, when screwing, the spiral screw lines of the pin and the box thread may not match, provided that they are made with using of tools with different values of the rake angle. Thus, it is lead to exceed the tolerances by one pitch. The algorithm allows to calculate the axial deviations of the screw line, depending on the value of the rake angle of the cutter for any of the points of the thread profile. It brings the fit of the cutters with a rake angle up to 5 ° to ensure the accuracy of the executed helices in the tapered thread machining.