| 摘要 |
PROBLEM TO BE SOLVED: To make the formation of an edge easy and prevent a significant defect from developing on the outlet side of a drilled hole in a wood to be worked. SOLUTION: A conical center auger edge 7 is protruded in the center of the tip of an auger body 2 with a helical discharge groove 5 for cutting which is axially long and has a specified lead, and a helical thread 6 is formed on the center auger edge 7. In addition, two bottom cutting blades 8 are formed linearly along the tip part of the helical discharge groove 5 for cuttings from the base part of the helical thread 6 upto an outer peripheral edge part 10. And the angle of refractionθof the bottom cutting blade 8 at a corner part 9 where the bottom cutting blade 8 crosses the outer peripheral edge part 10 is to be at most 0-90 deg..
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