| 摘要 |
The drilling tool comprises a clamping shank, a short transitional portion 4 adjoining same and a substantially cylindrical cutting portion (3) which has two diametrally oppositely disposed flutes (8,9) which turn through less than 360 DEG , two lands (10) which remain between the flutes and at its front end two replaceable cutting bits (6, 7) which are arranged in mutually displaced relationship through about 180 DEG in the peripheral direction, at different radial spacings from the drill axis (A). The flutes (8, 9) are of decreasing depth, beginning at the front end of the transitional portion to the rear end thereof, and run out into the peripheral surface of the transitional portion at the rear end thereof. The pitch angle of the two flutes (8, 9) increases from the front end of the cutting portion (3) to the rear end thereof. In the rear region of the cutting portion (3) the pitch angle ( beta 1) is so selected that at the front end of the transitional portion, where the flutes (8, 9) are still of their full depth, the centre line of each of the two lands (10), which centre line passes through the cross-section at that point (connecting cross-section) of the cutting portion (3), extends substantially in the direction of the overall resultant of the cutting forces acting on the cutting bits (6, 7). <IMAGE> |
