| 摘要 |
PROBLEM TO BE SOLVED: To provide a small diameter drill for machining a printed wiring board most suitable for a high speed spindle brought into practical use and be excellent in cutting quality and chip discharge ability. SOLUTION: A small diameter drill for machining a printed wiring board is formed in the shape of a round rod in appearance and comprises a shank; and a cutting edge part 2. A cutting edge 3 is disposed at the tip of the cutting edge part 2 to form a tip angle. At the rear end of the cutting edge 3, two chip discharge grooves 4 symmetrically stretching along an axis with a twist occurring are disposed at a rear end from the cutting edge 3. The diameter D of a shank is set to 1.5-2.5 mm at which the influence is not exercised by a centrifugal force and a drill grasping force is ensured. A core thickness (t) is 20-40% of a drill diameter, chip discharge ability is improved and a twist angleθis set to 35-45 deg. with a purpose of improvement of cutting quality.
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