What Is an Electric Spindle (built-in spindle, motorized spindle) and Its Applications?

Posted on Feb 18, 2019

Electric Spindle Built-In Spindle Motorized Spindle & its Applications

The spindle is one of the key components of the machine tool, the changes in its market reflect the development trend of the current machine tool industry to a certain extent.

As more and more machine tools develop towards high speed, high precision, high efficiency, high intelligence and functional integration. Quality components not only determine the longevity of the electric spindle but they also determine how the spindle handles speed, torque, and vibration. Besides the fact that electric spindle motor is better for energy consumption, balancing to achieve high­-speed Operation and good quality of product It has been proved that build in spindle last way longer than the Conventional ones.

When you start to Research spindle technology, you find the motorized spindle is often at the center of the discussion, and it can get mind-boggling, especially with the acronyms flowing freely an overview of key considerations when researching a CNC machining center’s electric Spindle, we will cover the highlights of its structure, technical, and few components function as well.

The motorized spindle as the rotating unit
In the modern machine tool industry, the spindle is the rotation axis and center of the machine tool. Articles are often used to refer to the entire rotating unit. The rotating unit includes not only the m spindle and its bearings, but also any accessories around it, such as chucks, cylinders, etc.
In the modern machine tool industry, a spindle is the rotating axis of the machine tool, and the spindle is usually designed as the center. This center rotary unit is called the spindle or article, and its scope includes the mandrel, bearings and surrounding parts. From this perspective, the electric spindles is one of the most complicated spindle types. Due to its driving characteristics, its power source comes from the inside of the spindle, and its motor is installed in the spindle sleeve.

The structure of a built-in spindle

The machine tool can be equipped with several different spindles, such as the headstock and tailstock spindles on a bench lathe, or primary spindle and secondary spindle on machining centers. The primary spindle is usually the biggest one installed at the primary machining unit. In the market, the reference to "spindle" has no further limitation, and only refers to the primary spindle.

Some machine tools dedicated to mass production have a set of four, five or even six spindles. These are called multi-spindle machine tools. Row drills and screw machines are multi-spindle machines that can be processed simultaneously. It is worth noting that although a bench lathe has multiple spindles, it is not called a multi-spindle machine due to its functionality of each spindle.

:: Read more : A Comparison of Direct Drive Spindle and Belt-Driven Spindle

Speed ranges of spindles

Regarding the spindle speed, the speed range definition is ambiguous. Generally, high speed spindles are used in machine tools in the field of metal processing, such as CNC milling machines. There are two different drive sources for high speed spindles:

- The belt driven spindle is composed of the spindle and the bearing shaft held in the spindle housing. The belt driven spindle is powered by an external motor connected with a pulley system.

- External motor source: The design can be modified to produce greater power and torque, with a speed range from 12,000 RPM to 15,000 RPM. The advantage is that speed switching is flexible and cost effective. At the same time, the disadvantage is that the maximum speed is limited, which will eventually limit machine applications.

- Integrated motor spindle: In this design, the motor is installed in the spindle sleeve. Due to the limited internal space of the spindle sleeve, the type and size of the motor will be limited, resulting in insufficient elastic power and torque, which may further limit the processing capacity.

Key Specifications

The following are highly recommended to be considered when someone decides to use, purchase or even repair a electric spindle :
1. Housing Diameter
Ø 100, Ø 120, Ø 150, Ø 170, etc.,

2. Taper
What kind of tool holder are you looking for! which is the components that hold your tool such as ER16, ISO25, HSK E-32, HSK-E40,HSK-A63, BT30, BBT30, BBT40, etc.

3. Bearing type & Specifications and Size
Front & Rear (Big/Small Ceramic Balls, Big/Small Steel Balls):


                                           Bearing Main Components
A-Outer ring(Race): Which Fit on the Housing
B-Cage; Which Separates the ball from another
C-Ball: which be arranged between the surface of the inner outer ones
D-Inner ring(Race): Which Fit on the shaft

Generally Speaking, Manufactures often use Angular Contact Ball Bearing in making high accuracy, high precision, high Speed, and low vibration Electric Spindle, in this article I’ll specifically highlight this type:


Angular contact ball bearing

4. Bearing Lubrication
A substance that reduces friction, heat, and wears when introduced as a film between solid surfaces. Using the correct lubricant helps maximize the life of your bearings and machinery, types: Grease, Oil-Air.

5. Bearing Preload
Bearing preload is the amount of force exerted against the bearing movement, proper preload maximizes bearing life and  Optimizes machine performance, bearing preload influences speed limits, Rigidity, And other applicable workloads, types:


● Spring
● Fixed Position

6. Driven Build in Motor
●Synchronous motor
●Asynchronous motor (AC Induction Motor)

Encoder, the encoder sends a feedback signal that can be used to determine position, count, and Speed or direction.

8. Installation Method
● Horizontal

9. Balance Grade
The balance calibration is to integrate the straight axis with the rotational axis, which is usually G1(ISO 1940) Grade.

10. CTS (Coolant Through Spindle)
Improves tool life, allows both deep hole drilling and blind pocket milling, It also allows high speeds and reduces cycle time.

11. Coolant
The Role of CNC Coolant in Machining are Three: Pure Water,  Air, Oil.

12. Run-Out
Run out is  an inaccuracy of rotating mechanical systems, specifically that the tool or shaft does not rotate exactly In line with the main axis. there’re several points you need to consider when purchasing a spindle, there’re four points should Be tested by a Test Bar and  Spindle Dial Indicator, Let’s Assume that the test bar length is 300 mm:


A- Taper Runout:                                  ≈ 0.002  mm
B- Taper Face Runout:                          ≈ 0.002  mm
C- Root of Test Bar Runout :                ≈ 0.003  mm
D- Test Bar Runout at 300mm :           ≈ 0.008  mm

Specific applications

The motorized spindle is mainly used in high-end precision machining, such as 3C wearing parts machining, work piece finishing, aerospace propeller cutting, engine cylinder machining, car chassis machining, transmission joint grinding, etc. The commonality of these applications is the need for rapid and flexible capabilities during processing.

Compared with other spindle types, the motorized spindles can obtain good processing quality by quickly switching the speed. Although its torque performance cannot be compared with that of a direct driven spindle, its average performance is relatively stable and stronger.  For example, a traditional CNC lathe may be equipped with spindle driven by a belt, but on a turning and milling center that requires complex machining, the work piece is usually fixed on a chuck, and the spindles are motorized spindles. The toughness of the cylinder may be higher. Therefore, if the spindle is driven by a belt, the teeth on the belt are likely to encounter gear errors, resulting in damage to the work piece or the machine.


Today built-in spindle has emerged as the most important component for any kind of high Machining process. As compared to the mechanical spindles the built-in spindles are have an Edge in terms of performance, high-end machining with improvised time and precision Process, which has become a key functional unit of high-speed machine tools and effectively Promotes the development of machine tool technology.

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