| 摘要 |
PROBLEM TO BE SOLVED: To provide a three-groove drill capable of highly accurately performing machining with a longer service life than that by machining by a reamer, without making incorrect the position of a hole made according to a pilot hole in finishing a cast hole of an aluminum alloy cast product even if the pilot hole is eccentric, and without generating chattering during machining. SOLUTION: This three-groove drill is made of high speed tool steel (may be made of cemented carbide) and has a chisel 1, three secondary cutting edges 3 extending outward from the chisel 1, a primary cutting edge 4 extending from each of the secondary cutting edge 3 to a leading edge 2 and three twisted grooves 5 to machine an aluminum alloy or the like. In the drill, a tip angleαis point-ground to 180 to 190°(centrally hollowed). COPYRIGHT: (C)2007,JPO&INPIT
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