The Influence of the Geometry of High-Performance Cutters on the Profile Accuracy of Large-Pitch Tapered Threads: Theoretical Study

Modern tool manufacturers offer fully profiled cutting cutters with an edge profile identical to the standard. The situation for large-pitch thread screws is significantly bigger because, for the most part, such tools have, at their disposal, special means for setting the cutting carbide insert and adjusting it to create an angle of inclination of the edge λ. This angle is required for an even load on both sides of the edge and to ensure the stability of the cutter before it is worn entirely. The modern scientific theory of the cutting process indicates the need to use another angular parameter - the rake angle, which enables the use of difficult-to-machine materials. Methodologically this theoretical study is about the functional influence of the combination of two angles: the inclination of the cutting edge and the back rake angle, on the accuracy of a large-pitch tapered screw thread made of heavy-duty steel. In this work, it is theoretically proven that for the smallest diameter drill-string tool-joint thread (NC10 thread), the combined influence of the geometric parameters of the back-rake angle γ = 12° and the cutting-edge inclination angle λ = 3, 74° on the accuracy of the half-profile angle of the thread is significant. At the same time, the deviation is 62.7% of the tolerance (±0.75°) according to the standard half-profile angle of 30°, which obviously indicates the minimum possibility of using high-performance cutters for the production of large-pitch tapered threads made of difficult-to-machining materials.