| 摘要 |
PURPOSE:To permit the boring with high quality for a long period by using a small-sized twist drill by improving the radiation of cutting heat by using a shank material having a thermal conductivity over 0.1cal/m.sec. deg.C. CONSTITUTION:A hard sintered part 21 is made of diamond powder in 85wt% and WC-15%Co as the rest, and a supporting part 22 is made of WC-12%Co, and a cylindrical body 23 which is made of composite sintered material and has a diameter of 0.7mm and a length of 15mm is brazed into the hole 26 on a shank 25 and fixed. Then, a small-sized twist drill is formed by working a cutting tip and a cutting groove. Said shank 25 is made of superalloy, and the material which contains WC-6% or WC-15%TiC-6%Co is used, and the thermal conductivity is 0.1cal/cm.sec. deg.C or more, and the hardness is over 25HRc. Since the heat generation at the cutter tip is dispersed through the shank 25, high-speed revolution is permitted, and the life of the cutter tip can be prolonged. |
