twist drills

Description

The twist drill is the most common type of drill. The shank of the drill is held by the machine tool, which in turn imparts a rotary motion. This shank may be straight or tapered. The body of the drill is typically made up of two spiral grooves known as flutes, which are defined by a helix angle that is generally about *0 degree but can vary depending on the material properties of the workpiece. The point of the drill generally form a **8° angle and includes a *0 degree clearance angle and chisel edge .The chisel edge is flat with web thickness of approximately 0.**5 x drill diameter. This edge can cause problems in hole location owing to its ability to "walk" on a surface before engaging the workpiece. In the case of brittle materials, drill point angles of less than **8 are used, while ductile materials use larger points angles and smaller clearance angles.