Boring is the process of enlarging holes that have already been drilled. In some cases, boring also indicates the process of drilling new large size holes. The technologies that are used for the boring process are known as boring mills or boring milling machines. They can consist of a single point bore cutting tool or a boring head having multiple tools.
Boring mills bring more accuracy into the boring process. With the help of boring milling machines, the bore of exact diameter can be cut. Without boring machines it is not possible to cut papered holes.

Boring machines:
The general purpose machines or lathes are used for boring, though they are not the specialized machines for boring. Machines that are specially designed for the process of boring are called boring mills or boring milling machines. A boring mill can be vertical or horizontal.
The cutting tools in boring mills can be made of carbide or high speed steel. A lathe work piece is used for boring operations of smaller size. Boring mills are used for larger work pieces. The commonly used work pieces are 1 to 4 meters in size. The maximum size is 20 meters. They can require 200 horsepower of power output. The coolant (the material used for cooling the boring milling machines) flows through the hollow passageway of the boring bar. During the process of boring, clutter and vibration are produced. They are controlled by the tungsten alloy disks. These disks are sealed in the cooling bar of the boring mill. The new machines have computerized and automated control features. They are more consistent and user friendly.

Considerations:
The considerations of the boring milling machines are outlined below.
Length to bore diameters should not be large as they cause deflection of the cutting tools. This results in the formation of unspecific and irregular holes.
The boring bar must be very strong and rigid.
Irregular working surfaces should be avoided.