Introduction to CNC Milling


From geometric dimensioning and tolerancing, to grinders, lathes and mills, there are a lot of different terms to know when it comes to the world of computer numerical control (CNC) machining. If you’re new to the industry, this can be intimidating — but once you learn the craft, these concepts become second nature.

An important concept for those who work in CNC machining to understand is CNC milling. This is a mechanical process that utilizes computerized controls and rotating cutting tools to create custom-designed parts.

So how exactly is this process used in the CNC industry? Keep reading to learn all about CNC milling — what it is, how a CNC mill works and more.

What Is CNC Milling?

Using computerized controls and rotating cutting tools, CNC milling removes material from the workpiece to create a finished product that meets the required specifications. This process can be used with a variety of materials, including plastic, metal, wood and glass.

When it comes to CNC machining, there are several different processes that can be used, including:

  • Mechanical
  • Electrical
  • Chemical
  • Thermal

CNC milling falls under the category of a mechanical process, since cutting and drilling is powered mechanically with no manual operation required.

How a CNC Mill Works

The CNC milling process follows the same steps many other machining types do, including making a computer-aided design (CAD) model, getting the CNC milling machine set up, and operating the machine to create the desired part. Here’s a quick step-by-step process:

  1. Create a 2D or 3D CAD part design and export it to a CNC file format, which is converted to a CNC machine program utilizing CAM software.
  2. The CNC program informs the actions of the machine.
  3. The operator prepares the machine by setting up the worktable and the workholding device, and attaching the milling tools and machine spindle.
  4. Using the machine interface, the operator will start the program and monitor it throughout the process to ensure everything is going smoothly.

Depending on the type of part that needs to be created, there are horizontal or vertical milling machines that can be used. Once the milling starts, the machine will rotate the cutting tool at incredibly high speeds— up to thousands of revolutions per minute!

This cutting tool can rotate in various directions and along multiple axes. It can create many different shapes, holes and any other impression the part requires. Milling is often used to add finishing details to a workpiece that has already been machined, but it can also be used to shape a piece of raw material from beginning to end.

Whether the material has been previously machined or not, a milling machine will gradually chip away at the material to create the desired shape. As the process goes on, it becomes more accurate and precise, so the finished part is within the right specifications.

CNC Milling Machine Parts

CNC mills are categorized based on the number of axes they can operate on. X and Y axes represent how the mill’s workpiece moves horizontally, and the Z axis refers to vertical movement. The W axis symbolizes diagonal movement. Most CNC milling machines operate on three to five axes.

A CNC milling machine at a UTI lab.

As one might expect, the makeup of a CNC milling machine is quite complex, just like the parts they create. While different machines can vary, they generally have these parts:

  • Frame/Base: The frame is the bottom piece that supports the machine. Essentially, it’s a base that provides stability during the milling process.
  • Spindle: The spindle is the top portion of a milling machine where tool holders can be installed. This part rotates as the part is being worked on.
  • Table: The table of a milling machine is what holds the workpiece for machining.
  • Axes: As mentioned, there are several different axes on a CNC milling machine: W, X, Y and Z. The machine operates on these axes depending on the requirements for the part.
  • CNC controller: The CNC controller is what controls the machine. It’s where the operator will input the G-code that dictates the functions of the machine.

CNC Milling Operations

The CNC milling process is versatile, so it’s used to support a variety of industries. There are different types of milling operations, including angular milling, form milling, plain milling and face milling.

Angular Milling

In this type of milling operation, single-angle milling cutters are used to create angular features, like grooves. The cutting tool is at an angle to the surface of the material being machined, and this angle is determined based on the design of the workpiece.

Form Milling

Form milling deals with irregular surfaces, like materials with curved surfaces. This process uses cutters that are specifically designed to work with these types of materials, like corner-rounding cutters.

Plain Milling

In plain milling, the cutting tool is parallel to the surface of the material being machined. This utilizes plain milling cutters, and both wide and narrow cutters may be used. Wide cutters are ideal for large surface areas, whereas narrow cutters can create deeper cuts.

Face Milling

Last but certainly not least, in face milling the cutting tool is positioned perpendicular to the surface of the material that is being worked on. Face milling cutters are used, which are ideal for creating flat surfaces and contours. This creates detailed, high-quality finishes to the part.

Train to Become a CNC Machinist at NASCAR Tech

Are you fascinated by the CNC industry and interested in learning more about processes like CNC milling? A career as a CNC machinist may be the perfect choice.

In UTI’s CNC Machining Technology program, you can gain the skills to craft performance parts and components from raw materials using processes like CNC milling.1 You’ll take courses on a variety of topics, including:

  • Basic Machine Shop Skills
  • Interpreting Blueprints / Layout
  • CNC Basics
  • Manual Machining Basics
  • CNC Milling
  • CNC Turning
  • CAD and CAM

The CNC program is offered at the NASCAR Tech campus in Mooresville, North Carolina, and can be completed in just 36 weeks. To learn more, visit our program page or request information to get in touch with an Admissions Representative today.

NASCAR Technical Institute Campuses That Offer CNC Training

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1.4 ) NASCAR Technical Institute is an educational institution and cannot guarantee employment or salary.
2 ) For program outcome information and other disclosures, visit

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