Drilling is the simplest of all machining processes

Drilling is widely considered one of the simplest and most common machining operations, accounting for approximately 25% of all machining processes. How Drilling Works—Basic Action: The process employs a rotating cutting tool with multiple cutting edges (typically a twist drill) to create a round hole in solid material. Two Motions: The process combines the rotation of the drill bit with a straight downward thrust (axial feed motion) toward the workpiece. Chip Removal: Small metal fragments resulting from the cut—known as chips—move up and out of the hole via the spiral grooves (helical flutes) on the cutting tool.

In workshops, it is often referred to simply as "boring," although this term is technically inaccurate. Drilling is defined as the process of creating a round hole using a twist drill. In contrast, "boring" refers to the process of enlarging an existing hole—typically using a boring bar—which can be performed on a lathe, milling machine, or drilling machine, not just a drill press. Figure 8.1 illustrates the drilling process.

Drilling is used to produce cylindrical holes. Creating a hole in a solid workpiece using a twist drill involves a material removal process characterized by significant chip-cutting forces. If high precision—such as dimensional accuracy or specific surface quality—is required for the hole walls, subsequent finishing operations using a counterbore or reamer are necessary.

During drilling, chips must exit the hole via the tool's helical flutes. Because the tool tip remains in contact with the material being cut, cooling the cutting zone is relatively difficult. Cooling is typically achieved by flooding the workpiece with coolant, spraying it, or delivering coolant through an internal channel in the drill bit.

The characteristics of the drilling process differ somewhat from other machining operations:

Chips must be evacuated from the hole being created.

Chips can cause problems if they are large or form continuous strands.

Creating deep holes can be challenging.

When drilling deep holes in large workpieces, coolant is delivered to the cutting edge through the center of the drill bit.