| 摘要 |
PURPOSE:For making holes with high accuracy, to balance the longitudinal force of cutting resistance by placing first and second tips, taking an approximate distance of 180 deg. there-between, and tilting said tips in opposite directions to each other. CONSTITUTION:One 31 of the four edges 31 of a first tip 3 tilts at the angles of 60- 85 deg. with the rotary shaft 7 of a drill 1 or cutting blade for cutting the inside of holes. The nose-round portion 32 adjacent to said cutting blade 31 positions at the very tip of said drill 1, and the virtual point thereof exists at the rotation center 7 of said drill 1. In the meanwhile, a second tip 4 has an almost 180 deg. phase difference from said first tip 3. The outside of said holes is alloted to said second tip 4, and said cutting blade 41 tilts at angle B (about 85 deg.-89 deg.30') with the rotary shaft of said drill 1. The inner one 43 of the two nose-round portions between which said cutting blade 41 is palced positions axially forward and diametrically inward of the outermost-circumferential nose-round portion of said first tip 3. In the meanwhile, the outer one 42 is set to the position for determining the diameter of a hole to be cut. |
