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The application of solid carbide tri-flute drills is important for machining high- precision holes. The main advantages of a tri-flute drill are high productivity, very good self-centering and relatively small deviation from the base axis of the hole. The profile of the helical chip groove in the radial section and the shape of the thinning of the drill are the most important factors controlling the cutting precision and overall performance. In this work, various types of groove shape have been investigated and a new method for designing and rationalizing the cutting part shape of a tri-flute drill has been developed. The key result of this paper is a new method of the design of the cutting edge with minimized change in the radius of curvature, which allows to more evenly distribute the force load in the cutting zone and, hence, to decrease the probability of the drill failure. A comprehensive study of the geometric parameters of the drill cutting edges allowed determining the necessary curvature with a minimum number of node points and accounting for the initial position of the transitional section and chisel edge angle. New relationships between the curvature of cutting edge and the shape of the chip groove derived in this work provide a theoretical foundation for the further development of practical recommendations for designing the high-performance tri-flute drills.
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