Milling Spindles Guide

What are Milling Spindles?

The milling spindles are the working components that are usually found in a CNC machining center. In a computer numerical control machining process, the milling spindles are responsible for carrying out the machining operations onto the workpieces. A milling spindle serves as a multi-machining tool interface to which the cutting tools or drill bits are mounted. The machining operations that the milling spindles are involved in are the cutting operations including milling, drilling, boring, reaming, or threading, etc. The milling spindles are typically referred to as the spindle or the CNC spindle.

To mount the drill bits or other types of cutting tools onto a milling spindle, a power-driven unit is needed. The power-driven unit that is incorporated with the milling spindles is responsible for the clamping, releasing, changing, and replacement of the cutting tools. In a modern CNC manufacturing setting, the release unit on the spindle can be hydraulically driven, pneumatically driven, or electrically driven. With the power-driven release unit, the change and replacement of cutting tools can be done rapidly and efficiently to reduce machine downtime and idle time.

In addition to the power-driven clamping and releasing unit, there are also manual clamping systems on the spindles of certain CNC turning centers. The manual clamping system is ideal when a CNC turning center is responsible for only one or a couple of machining operations and the change of the cutting tools is less frequent. Since the CNC lathes to date are usually multi-functional, the power-driven clamping systems are preferred in most machining settings to the manual systems.

How do milling spindles work?

The primary components of the milling spindles are a motor, a taper for holding tools, and a shaft that holds together all the components. The electricity-powered motor drives the spindle to rotate. The taper is the spindle head. All the cutting tools are mounted onto a spindle through the taper. On a conventional milling spindle, the taper only allows a piece of the cutting tool; to date, there are multi-spindle heads that allows multiple sets of cutting tools on a single milling spindle. This allows the production to be improved in a more efficient manner.

In a machining operation, the spindle rotates along a single axis or multiple axes on a CNC lathe. When the spindle rotates, the cutting tool that it clamps will spin accordingly. The spindles rotate at a high speed so that when the spinning cutting tool leans against a workpiece, it cuts through the workpiece and trim the workpiece into the desired shape or drill holes on the surfaces of the workpiece. The spindles are often powered by electricity while some of the machining lathes have the spindles powered by pressurized air.

3-axis machining

The spindle heads are traditionally used without the capability of movements. It is a stationary machine that stands on a machining lathe. With this type of spindle head, the cutting tools can only advance toward the workpieces at a very limited distance. The use of the spindle in this style is less efficient since the workpieces can only be machined on one side at one angle. Machining the workpieces on a different side could be hassling and machining on complex surfaces was challenging as a result. Yet, as the technology progresses, the milling spindles have evolved into another level where multiple axes machining is enabled.

Generally speaking, the modern milling spindles on a CNC lathe usually have the capability of 3 axes machining. The 3 axes machining refers to the movement of the cutting tools on the spindle head. The cutting tools can move along three separated axes to machine the workpieces on 3 axes machining spindle head. The movements are back to front, side to side, and up and down. To achieve movement, the cutting tools are held by the spindle head horizontally or vertically while the machining operation is ongoing.

5-axis machining

In addition to the three axes machining, there are even more advanced spindles and turning centers that allow five axes machining. Unlike the three axes machining that allows the X, Y, and Z-axis movements, the five axes machining allows two additional axes, the A and B axis. Having the five axes machining capability, the spindle is able to perform machining operations on the workpieces at almost every angle from all directions.

Though the machining capability of the three axes turning center is more limited than the 5 axes counterpart, the setup and preparation time of it is alternatively shorter and simpler. That being said, with the CNC system, the digital controls make the five axes machines more user-friendly. The five axes machines are ideal for deeper parts made from harder materials with more complicated surfaces. In addition, the time a five axes spindle lathe takes to complete an operation is also a lot faster.


In different types of CNC manufacturing settings, there can be particular applications of a milling spindle. The multi-functionality of a spindle is based on the cutting tools it can work with. With more types of cutting tools, the spindle can perform more types of machining operations accordingly. Besides the manufacturing application, the spindles can be utilized in other lines of the industry as well. For example, milling spindles are commonly included in automotive applications, mold manufacturing, the electronic industry, and even aerospace applications.

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