DRILL

To provide a drill that can improve defect resistance of a cutting blade of a small-diameter drill and at the same time make both tool stiffness and chip discharging performance compatible.SOLUTION: A drill 10 has two or more cutting blades 1 and 2, where a diameter φD0 thereof is in a range of 0.5 mm or more and less than 1.1 mm and a groove length L0 thereof is in a range of five times or more and 12 times of less of the diameter φD0. An angle α0 of a tip of the drill 10 is in a range of 118° or more and 122° or less, and a core thickness φD1 of the drill 10 is set to be in a range of 0.29 times or more and 0.38 times or less of the diameter φD0. Further, the cutting blades 1 and 2 apply R-chamfering in a range of 6 μm or more and 10 μm or less.SELECTED DRAWING: Figure 2 【課題】小径ドリルの切れ刃の耐欠損性を向上させると同時に、工具剛性と切りくず排出性を両立させたドリルを提供する。【解決手段】二以上の切れ刃１，２を有して、直径φＤ０が０．５ｍｍ以上１．１ｍｍ未満の範囲であり、溝長Ｌ０が直径φＤ０の５倍以上１２倍以下の範囲であるドリル１０において、ドリル１０の先端角α０は１１８°以上１２２°以下の範囲であり、ドリル１０の心厚φＤ１は前記直径φＤ０の０．２９倍以上０．３８倍以下の範囲とする。また、切れ刃１，２には、６μｍ以上１０μｍ以下の範囲でＲ面取り加工を施す。【選択図】図２