The Basics of CNC Milling

Computer numerical control (CNC) machining is a machining process where code is programmed into a computer by an operator. This code (CAM or CAD) contains directions that offer precise movements for multi-point tools to follow in order to remove material and create a final product. CNC machines are faster, more efficient, and safer than manual milling machines. There is a variety of types of CNC machining, such as CNC milling, CNC turning, and CNC drilling. This article will explore CNC milling services. Specifically, how the CNC milling process occurs, as well as common CNC milling machine operations and materials for a CNC milling machine.

What Is CNC Milling?

CNC milling is very similar to drilling or cutting. However, unlike traditional milling, it can move along multiple axes. Most CNC milling machines operate 3 to 5 axes, although there are also 2- and most recently, 6-axis CNC milling machines.

How Does CNC Milling Work?

The process for using a CNC milling machine is similar to how all CNC machines function. First, someone will design a Computer-Aided Design (CAD) model. This CAD model is a 2D or 3D representation of what the part will look like. Computer-Aided Manufacturing (CAM) software will convert the CAD file once it is exported to a file that the CNC milling machine can read (usually using G-code).

The operator will use the machine interface to execute the program once they have set up the worktable or vise, attached the workpiece to it, and fitted the appropriate milling tools to the spindle. The attached tool will then work against the material by generally shaving off small pieces before switching to a more precise milling that is necessary for complex parts that require high precision and a low margin of error.

There is a range of milling machine operations that may be possible, and some of the most common are plain milling, face milling, and angular milling. Examples of less common operations include gang milling, gear cutting, and profile milling.

Milling Machine Considerations

As mentioned above, CNC machines come with multiple axes of operation. A milling machine (unlike a drill or turning machine) can cut at different angles. The number of axes determines the machine’s operations. A 2-axis milling machine can cut vertically and horizontally, but only in one direction. In contrast, a 5-axis milling machine can rotate along the x- and y-axes. Each axis adds a layer of complexity to what the milling machine can accomplish. A 5-axis machine, however, is not always the best CNC milling machine; it can have a slower or faster operation speed than a 3-axis and a 4-axis machine, dependent on the configuration.

This is part of why it’s critical to understand the layer of precision and complexity required for the necessary parts.

In addition to the number of axes, CNC milling machines also are categorized by whether they are vertical or horizontal. Vertical and horizontal refer to the direction of the machine’s spindle. If a machine is vertical, the spindle is oriented in a fixed position, and the workpiece will move up or down in line with the tool on the spindle. If the machine is horizontal, the spindle is horizontally oriented, as one might expect. Horizontal machines are more complex than vertical machines and usually require arbors for extra support.

Milling machines are classified by configuration. Some of the most common include knee-type and planer-type.

Material Selections for CNC Milling Machines

A variety of materials work well with CNC milling, as long as the type of material can be physically drilled. Most CNC mill machines work with metal materials such as alloys. Other possible materials might include glass, ceramics, and composites. Many materials require specific CNC machine tools that take into consideration the material’s density as well as the available rotation of the cutting tool. A milling cutter that’s meant for wood would most likely break if it were used with steel material, for example.

Alternatives to CNC Milling  

Depending on the need, a different machining process might be a better selection. This could include other subtractive processes, such as CNC drilling and CNC turning, or it could include an additive process such as 3D printing. The best selection will depend on the specific needs of the project at hand. There are many factors to consider when a manufacturer is exploring whether or not CNC milling services are the optimal choice. This post has explored a handful of considerations; however, more remain.

Paul Guerdo

Paul Guerdo