Threading Technology – Clamping Technology 520

423 Twist Drills STEEL VA Accessories 3 x D Tech. Info v c / f Product Finder 5 x D 6 x D 8 x D 2-3.5 x D 5.7 Point angle Centering and pilot hole With large clamping-related extension lengths, it is necessary to provide either a centering or a pilot hole. With tool lengths exceeding 8 x D, it is highly recommended to either start drilling with reduced feed, or to provide a centering or a pilot hole. ≥ 140° 135° Centering Please note that the point angle of the first, or preparatory drill must be larger than that of the subsequent drill. We recommend our twist drills EF-Drill acc. DIN 6537 K. The centering should not be deeper than the point length l 5 . 135° 140° z.B. ø 10 h6 = +0 –9 z.B. ø 10 m7 = +21 + 6 Pilot hole A pilot hole is used for deep-hole drilling. Please note that the point angle and the diameter of the pilot drill must be larger than those of the subsequent drill. For the pilot hole, a depth of 1 x D is sufficient. 5.6 Coolant supply Internal cooling is always to be recommended when drill depth exceeds 2 x D. From a drill depth of 5 x D, it is absolutely necessary. With external cooling, make sure to provide not only sufficient coolant pressure but also the right type of supply. Wherever possible, three coolant-lubricant jets should hit the twist drill directly. Bad coolant supply Good coolant supply Vertical machining Good Better Horizontal machining