| 摘要 |
<p>PCT No. PCT/FR93/01214 Sec. 371 Date Aug. 4, 1994 Sec. 102(e) Date Aug. 4, 1994 PCT Filed Dec. 9, 1993 PCT Pub. No. WO94/13421 PCT Pub. Date Jun. 23, 1994A precision twist drill bit provided with two helical teeth separated by grooves. According to the invention, its diameter is equal to the minimum diameter of the hole to be drilled plus 0.005 mm, the width of the land (3) lies in the range 0.1 mm to 0.2 mm, neither tooth is ahead of the other, the end is ground so that it has two slopes with pits (4) that radiate from the center, the cutting edges (1, 2) of the two pits (4) are symmetrical, and all of the surfaces of the drill bit are polished to within an accuracy of less than 0.1 microns Ra.</p> |
