The main difference is that by drilling, you receive a hole; by boring, you enlarge its diameter; and by reaming, you give it a smooth finish. All three manufacturing processes are intended to process a workpiece, so holes in its design have precise dimensions, respond to specifications, and look nice. 

We examine how different these three processes are, so you always may know which one suits your specifications and purposes at a particular moment. As a bonus, we reveal some similarities between them.


What is Drilling? Technical Specifications and Features, Pros and Cons

Let’s start by discussing the basic process of making a hole – drilling.


Description of Drilling

Drilling is one of the simplest manufacturing processes. It is typically done by using a manual or CNC drilling/ milling machine or lathe and a cutting tool known as a drill bit. The center holds tooling in a spindle, which is rotated at high speed up to thousands of revolutions per minute (RPM). 

In its turn, a drill bit has cutting edges that are passed against the workpiece. Tooling cuts the material by removing small metal chips from its surface. As a result, a rough hole is obtained.

CNC Drilling Machine

Tech Specifications and Distinctive Features


Advantages and Disadvantages

Manufacturers love drilling for the following:

And here’s the list of disadvantages:


What is Boring? Technical Specifications and Features, Pros and Cons

Then, we proceed to adjusting a previously drilled hole to any diameter – boring.


Description of Boring

Boring is the process of enlarging the already existing hole. Unfortunately, after drilling, the diameter of a hole is not accurate. A smaller hole is drilled and then enlarged to ensure the maximum precision possible.

For this purpose, a boring bar is used. A machine, typically, lathe or milling CNC center, holds the single point tooling and deepens it into the hole. A spindle with a boring bar fixed into it rotates at speeds of hundreds of RPM, cutting off small chips of material until the necessary dimension is achieved.


Tech Specifications and Distinctive Features


Advantages and Disadvantages

Manufacturers love boring for the following:

And here’s the list of disadvantages:


What is Reaming? Technical Specifications, Features, Pros and Cons

Finally, we give a smooth finish to the already drilled and bored to precise dimensions hole – reaming.


Description of Reaming

Reaming is the finishing process intended specifically for previously created holes. It ensures great precision of smoothness of inner surfaces of holes without changing their dimensions significantly.

For reaming, cutting tools as reamers are used. They are basically rotary cutting bits with a cylindrical or conical shape. A spindle of a CNC machine holds a tool and rotates it at low RPM. Sharp edges of tooling cut off microscopic ships of material, typically metal, thus polishing internal dimensions to perfection.


Tech Specifications and Distinctive Features


Advantages and Disadvantages

Manufacturers love reaming for the following:

And here’s the list of disadvantages:

Drilling Boring and Reaming

You can familiarize yourself with schematic visualizations of all the three processes in the infographics below.


Drilling vs Boring vs Reaming: Comparison Chart

  Drilling Boring Reaming
Purpose To create a new, rough hole (first phase of fabrication process). To enlarge the existing rough hole to precise diameters (second phase of fabrication process). To finish inner surfaces of the prepared hole (third and final phase of fabrication process).
Type of tooling Drill bits – double point tools, with cutting edges called flutes. Boring bars – single-point tools. Reamers – multipoint tools, with a number of flutes equal 4 or more.
Quality of Surface Rough surface, inappropriate for further use. Precise dimensions and better surface quality. Acceptable for some components where hole diameters are not crucial. The greatest accuracy possible. Sufficient for any use.
Possibility of variations You can regulate the diameter of a drill bit to a certain extent and adjust any hole’s depth using proper tooling. It is not intended to regulate the depth of holes but successfully adjusts diameter to nearly any dimension required. It does not change the depth of a hole or its diameter but just slightly adjusts dimensions in the process.
Production rate The speed of material removal during drilling is the highest. Boring is performed at a much lower RPM than drilling. This process is the slowest.
Technical requirements Drilling requires only the flat surface and appropriate drill bit to be fixed in the spindle. Boring requires a previously drilled hole and an appropriate boring bar to be chosen. Reaming requires a previously drilled and bored hole and the reamer with equal to the hole dimensions.

What are the Similarities Between Drilling, Boring, and Reaming?

Despite all the three processes being rather complementary than mutually exceptive ones, we managed to list major similarities between them.

  1. All of them participate in the process of holes creation.
  2. They employ cutting tools to fulfill their purposes.
  3. Are based on the material removing manufacturing process.
  4. They can be performed on the same CNC machines.
  5. Require flat surface of a workpiece and feeding a cutting tool at the right angle

In essence, drilling, boring, and reaming are vital pieces of the same process of hole making and can be regarded as complementary operations.


Final Take

Here’s a big idea: you almost always need all the three processes employed to adhere to modern components’ specifications. 

Drilling is a great way to originate a new hole in a flat surface, while boring can effectively adjust it to the required diameter. Finally, you should use reaming as a finishing process. As a result, you obtain a perfect hole with diameters that are as precise as possible.



You may have thought that you could simply choose the appropriate drill bit to make any hole, but it is incorrect. Drilling is a rough process. Typically, to make an appropriate hole, a smaller hole is drilled and then bored to the necessary diameter with great precision. 

Even if you have holes of your workpieces precisely bored, you still need to polish their inner surfaces, or dimensions may slightly differ from ones indicated in tech specifications. In case this nuance is not critical, you may abandon reaming. 

From our experience, reamers can be used to make a new hole in soft metals. But, it is counterproductive and will likely result in poor dimensions overall and severely reduce the tooling life of a reamer.