| 摘要 |
PURPOSE:To reduce breakage of tools by providing a non-cutting-edge portion with specific width in a restricted position of each side, and by obtaining complete cancel of the bending moment owing to the cutting resistance. CONSTITUTION:Portion necessary for cancel of bending moment are A-F1, B2- F2, and if the portions F1-G1, F2-G2 have an angle space of 180 deg. for every possible shape, the edge width and top angle can be selected to any value, so that the same portion can be used commonly for A-F1 and B2-F2. For ex., the additional peripheral cutting edges 12, 23 correspond to F1-G1, F2-G2. Accordingly the drill outside dia. can be adjusted by changing its position. The additional peripheral cutting edges have a large cutting speed, but as small a cutting thickness as 1/2 to provide the tool with a prolonged life. |
