Page 223 - Demo

221DEEP HOLE DRILLINGGundrill StructureA gundrill consists of three main elements: cutting tip, also called drilling head (working part), tubular stem with a V-shaped external groove, and shank also called driver (Figure 6.5.2.1).Figure 6.5.2.1Tubular stemCutting tip / Drilling headShank / DriverCutting Tip / Drilling HeadThe drilling head is tapered on its length to reduce friction (Figure 6.5.2.2). The taper angle depends on the type of material to be drilled. For high precision drilling, the taper should be reduced to a minimum. The low taper angle has very high straightness control and good surface finish, but at the same time, poor tool life and high risk of tip jamming in the hole. The high taper angle has better tool life (especially in shrinking materials) and a lower risk of tip jamming in the hole, but at the same time on bad straightness control. It should be noted that when the head is resharpened, the diameter of the drill changes, affecting the hole tolerance.Figure 6.5.2.2Back Taper AngleBack Taper AngleThe key variables of a cutting tip are point location, nose angles, and pad form.