Calculation of the Accuracy of the Drill-String NC13 Thread Profile Turned from Difficult-to-Machine Steel

The process of drilling wells is accompanied by significant environmental pollution. From time to time, it is proposed to make threaded connectors in drill strings from high-strength and stainless steel to reduce emissions. Such steels are difficult to machine, requiring negative rake angles of threading lathe cutters. The article proposes an algorithm for calculating the accuracy of the thread profile to determine the possibility of turning it using such cutters. The result of the predictive calculation proved that using a tool with a rake angle of −7° for turning an NC13 drill thread can lead to a deviation from the nominal value of the half-profile angle, which is 40% of the size tolerance. It was shown that such a deviation could be avoided if a tool with a zero rake angle was used on the lust finish infeed of 0.035 mm.