Operations Performed on Drilling Machine

Drilling: The operation of producing a circular hole by removing metal by rotating the cutting edges of a drill is known as drilling. Metal is removed by shearing and extrusion (Figure 19.31). Drilled hole is slightly oversized due to non-alignment of the tool and vibration of the spindle. For producing accurate hole, the drill bit selected is slightly smaller than the hole diameter required. After producing the hole reaming is required for finishing.

Figure 19.31 Drilling

Reaming: It is an operation to produce a finished hole after drilling. Since the material removal rate in reaming is very less (0.4 mm), therefore it is rarely used for enlarging the hole. Reamer has straight teeth which is given a rotational motion similar to drilling. The reaming operation is shown in Figure 19.32.

Figure 19.32 Reaming

Boring: It is an operation to enlarge the drilled hole. It has single cutting point cutter as shown in Figure 19.33. In boring, material removal rate is larger than that of drilling. Therefore for enlarging purpose, boring tool is used in place of large diameter drill bit.

Figure 19.33 Boring

Counter Boring: The operation of enlarging the end of a hole cylindrically, as recess for a bolt head, is known as counter boring. The counter boring process is shown in Figure 19.34.

Figure 19.34 Counter boring

Counter Sinking: The operation of making a cone shape enlargement of the end of a hole, as for accommodating the screw head, is known as counter sinking (Figure 19.35).

Figure 19.35 Counter Sinking

Spot Facing: The operation of squaring and smoothing the surface around a hole, as for the seat for a nut or head of a bolt, etc., is known as spot facing (Figure 19.36).

Figure 19.36 Spot Facing

Trepanning: The operation of producing a large hole (diameter over 50 mm) by removing metal along the circumference of a hollow cutting tool, which enters the small previously drilled hole to produce the larger hole concentric is known as trepanning (Figure 19.37). It is used for the diameter more than capacity of particular machine and where hole depth is much more in comparison with normal work.

Figure 19.37 Trepanning