Prediction of the accuracy of the tapered thread profile

Abstract

The efficiency of drill string largely depends on the pipe-end connector’s accuracy named tapered thread tool joint. Most of those are made by using lathes. Turning tools were made with a profile identical to the thread profile, and all well-known world brands’ plants make the back rake angle of such a cutter with zero value. This is obviously due to the lack of a precise algorithm for calculating the cutter profile and ensuring the accuracy of the tapered thread profile. A virtual experiment was carried out of three-dimensional modeling of the process for shape creation. It showed that in the case of lathe machining of the thread of NC23 type, the deviation from the nominal half profile of the obtained thread is only 0.02°. This result prompted the decision to propose a new algorithm for predictive calculation of the half-angle of the cut profile based on the parameter associated with actual turning – the working height of the profile – h in contrast to previous scientific sources where this calculation was based on the parameter H – not truncated thread Height which is associated with the theoretical base of the accuracy of the thread. The result of the program application, created based on the algorithm proposed in the article, showed that the predicted accuracy of the obtained profile’s half-angle could be in a range from –0.03° to +0.10°, which is equivalent to 4–13 % of tolerance of this dimension.