Drilling is the operation of cutting a cylindrical hole by a rotating tool called drill. Before the process of drilling, the center of the hole is positioned on the work piece. Two lines at right angles to each other are drawn. A center punch is used to mark the center point at the meeting of two lines. The rotating drill is pressed at the center point scribed on the work piece to produce the hole. It Is performed on drill press
Drilling does not produce a precise hole. Only rough internal surface will be produced by the drilling process. The hole is lightly bigger than the size of the drill bit used due to the vibration of the drill.
the process of sizing and finishing the already drilled hole is called as Reaming. The tool used for reaming is known as a reamer. It is a cylindrical tool having many cutting edges. Reamer cannot drill a hole.
It simply follows the path of an previously drilled hole. It removes a very small volume of metal. The volume of metal removed in reaming is approximately 0.375mm. In this process the spindle speed is half that of drilling process.
Boring is a process of increasing a hole with the help of a single point cutting tool. Boring is done where right size drill is not available. If the size of the hole is very large the hole cannot be drilled. Then to enlarge the hole boring is performed.
By boring, the hole is finished accurately to the required size. The internal surface of a hole in a casting is machined by this boring process. The cutter is held in a boring bar which has a tapped shank to fit into spindle hole.
The operation of enlarging the end of a hole cylindrical is known as a counter boring. The operation of making a cone-shaped enlargement of the end of a hole is known as countersinking.