Hole Making Operations in CNC Machining

September 14, 2020

Machining is a type of material removal process that creates specific products on a part by removing and cutting away any unwanted material from the workpiece. This process is typically done and performed by computer numerical control (CNC) milling machines or CNC turning machines. Other pieces of equipment that can conduct machining include drill presses and tapping machines.

Conducting this material removal process with CNC machines can result in various hole making operations that are often utilised by various industries. Hole making operations are intended to cut holes into any given workpiece, which typically works in conjunction with other machining operations.

To date, numerous types of hole making operations can be done by the manufacturer to achieve their desired workpiece results.


Drilling is a hole making operation that maximises a drill bit to cut a blind hole or a through-hole in a solid material or workpiece. Typically designed with a pointed end, a drill bit usually enters the material axially and is pressed against the workpiece before rotating at a rate of hundreds to thousands of revolutions per minute. Some types of drill bits that are often used for drilling operations include twist drills, centre drills, spot drills, and tap drills.


Similar to drilling, reaming is a type of hole making operation that can also remove certain parts of material from a workpiece. However, reaming is usually done to enlarge an existing hole in a material, which is far from the drilling’s ability to cut new holes. The tool used for reaming is a reamer, which can enter a workpiece axially. Reaming is typically done after drilling to achieve a more precise hole diameter and a smoother, sleeker internal finish and look.


Tapping is typically done to cut internal threads inside an existing hole, which enables the hole to be threaded with cap screws or bolts. This hole making operation is also done to provide appropriate threads for the nuts. During the tapping process, a suitable tap drill size will drill an existing hole for it to easily accommodate the desired tap. It is important for this process to use a tap that has a similar major diameter and pitch of the threaded hole.


The tool used for the boring process is a single-point cutting tool that can easily cut through a workpiece with the required diameter by its adjustable boring head. The same tool enters a material axially as it cuts the internal surface of an existing hole and enlarges the hole’s diameter. The purpose of boring operations is to achieve more precise dimensions and polish any previous finishing operation that has been done to the workpiece.


Counterboring is a hole making operation that enlarges the top portion of an existing hole concentric with the original hole. It is often done after drilling to effectively accommodate the heads of fasteners such as bolts, studs, and pins. Just like other hole making operations, the tool utilised in this process also enters the workpiece axially. Counterboring tools likewise contain cutting edges that have either straight or spiral teeth and a pilot on the end that helps them cut straight to the existing hole.


Countersinking is a type of hole making operation that produces a cone-shaped edge opening surface of an existing hole. This process is normally done to deburr a drilled or tapped hole. It also allows the head of a countersunk-head fastener to sit flush with the workpiece material. The tool used for this process enters the workpiece axially and can create countersink angles between 60 and 120 degrees. The most common degrees for countersinking are 82 and 90 degrees.

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