JPS6445504A - Hole cutting tool - Google Patents

Abstract

PURPOSE:To reduce burr so as to enhance accuracy of a hole finished surface by providing notches along chip grooves on the outer periphery sides of the main cutting blades of a drill so that finished cutting edges have positive rake angles so as to determine a shape not obstructing the flow of chips. CONSTITUTION:On the respective outer periphery sides of main cutting blades 1, 2 notches 70, 80 are disposed in parallel with chip grooves 10, 20, and the respective intersecting lines of the front ends of the notches to the extending faces of flanks 5, 6 with respect to the main cutting blades 1, 2 serve as finished cutting edges 7, 8. Thereat, the respective angles alpha of the finished cutting edges 7, 8 between land portions 71, 81 at points S, T are set at less than 90 deg.. In addition, the respective angles beta of lines 72, 82 connecting M, N to the finished cutting edges 7, 8 between MA, NB are also set at less than 90 deg.. Therefore, the tip angle of the finished cutting edge becomes larger than that of a drill, and as well the rake angle of the finished cutting edge also becomes larger so that the cutting quality of the cutting edge becomes more preferable. Consequently, burr can be reduced, thereby improving the quality and accuracy of a hole surface.