| 摘要 |
A non-core drill bit is provided with a metallic seat 2 attached to the tip of a shank of a boring tool, a cylindrical first diamond grindstone body 3 fixed to the metallic seat 2 and having a recessed cutout portion 10 to be opened to one side, and a second diamond grindstone body 4 installed inside the recessed cutout portion 10. The tip of the second diamond grindstone body 4 is positioned on the metallic seat 2 side from the tip of the first diamond grindstone body 3. The inner side of the tip face of the first diamond grindstone body 3 is preferably formed in an approximately reverse-conical recessed shape.
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