In machining, boring is the process of enlarging a hole that has already been drilled (or cast), by means of a single-point cutting tool (or of a boring head containing several such tools), for example as in boring a gun barrel or an engine cylinder.
![CNC Line<br>Boring](https://www.mprracingengines.com/wp-content/uploads/2017/10/MPR-Racing-Engines-CNC-Line-Boring-1000x658.jpg)