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What are the traditional end mill holder types

End mill holders can be broadly classified into the following categories: Spring collet end mill holders; Thermal shrink-fit end mill holders; Hydraulic end mill holders; Other end mill holders

Spring collet end mill holder

Spring collet end mill holder

Also known as ER end mill holder, it is widely used in practice due to easy end mill installation and large end mill clamping force (of course at a relatively affordable price level). It connects, removes, and secures end mills using a tapered collet that expands and contracts. Spring collet end mill holders come in various shapes to hold round or end mill shanks. Therefore, they are sometimes used on lathes. For CNC machine end mills, there are mainly two types of spring collet end mill holders: “push-in” type and “pull-in” type.

In the push-in type, the collet is pushed inwards for clamping by rotating the nut at the front end of the collet.

Pull-in type works by using a screw at the bottom of the collet to pull the collet inwards for tight clamping of the end mill.

Thermal shrink-fit end mill holder

Thermal shrink-fit end mill holder

Thermal shrink-fit end mill holder utilizes the property of thermal expansion and contraction of metal materials for clamping end mills. The working process is as follows:

First, the end mill holder is heated using a thermal shrinkage machine.

Then, the end mill is inserted into the expanded inner diameter of the end mill holder due to heating.

Next, the end mill is cooled with water or other coolant.

As a result, the inner diameter of the shank contracts, and the end mill is clamped tightly.

A thermal shrinkage machine is required to complete this process.

This method has higher rigidity and less run-out accuracy compared to other end mill holders, making it effective for hard material machining and high-precision machining using small-diameter end mills.

The use of a thermal shrinkage machine eliminates dependence on operator skill levels. The repeatable connections are also a key advantage of this method.

Hydraulic end mill holder

Hydraulic end mill holder

The principle of a hydraulic end mill holder is similar to a hydraulic cylinder. It uses adjusted oil pressure through screws to clamp and secure end mills. An operator can easily hold the end mill with a hex wrench. Hydraulic end mill holders have extremely high run-out accuracy, typically suitable for precision machining operations.

Moreover, the oil has a high ability to absorb vibration energy and reduce vibrations during machining. However, compared to other types of end mill holders like spring collet end mill holders (ER end mill holders), there are some rigidity issues. Therefore, end mill holder manufacturers are working on developing hydraulic end mill holders with even higher rigidity.

Other end mill holders

Other end mill holders

In addition to the three types described above, there are many other end mill types for machining centers, such as indexable cutter blocks for mounting indexable inserts, drilling chucks for holding drills on drill presses, end mill holders for tapping, boring bars for boring, etc.

Angle heads are also a type of machining center-end mill holder. Angle heads have a different structure from conventional end mill holders by allowing the end mill machining direction to be changed to specific angles, thus enabling additional axes to be added to existing machining centers for machining. Therefore, by effectively utilizing angle heads, various machining operations can be done by fixing the workpiece to the table just once, improving machining efficiency.

It’s worth emphasizing the choice of angle heads – they are generally classified into domestic, Taiwanese, European, and Japanese brands. It is recommended to choose reputable brands for products like angle heads, because positions, where angle heads can be used, involve high-precision machining, so non-branded options should not be tried lightly. Most angle heads are non-standard products tailored to each machine end mill model and requirements, predetermining their non-universal nature.

How to correctly select and install different end mill holder types?

Select the suitable end mill holder type based on machining requirements, and install it according to instructions to ensure secure clamping.

What are the common end mill holder maintenance methods?

Cleaning filters, checking seals, replacing hydraulic oil, etc.

What equipment is required for a hydraulic end mill holder?

A hydraulic system including an oil tank, pump, filters, etc.

What is the main function of an end mill holder?

To securely clamp the end mill on the machine spindle for machining operations.

What do you need to pay attention to in the maintenance of the hydraulic end mill holder?

1. Regularly replace and clean the filter to ensure the filtration system works properly.
2. Check for leaks and carry out timely maintenance and repair. Replace old hydraulic oil on schedule with qualified new oil.
3. Set oil pressure limits. Adjust the maximum working oil pressure limit of the system as needed.
Regular maintenance can effectively extend the service life of the hydraulic system and ensure the reliable operation of the end mill holder.

What are the advantages and disadvantages of hydraulic end mill holders compared with spring end mill holders?

The advantages of a hydraulic end mill holder are high rigidity, small end mill run-out, and suitability for precision machining. The disadvantages are higher cost and lower rigidity compared to a spring collet end mill holder.
The advantages of a spring collet end mill holder are low cost and relaxed requirements for end mill holder shape and size. The disadvantages are lower rigidity, general precision, and more difficult clamping/unclamping operation compared to a hydraulic end mill holder.
Overall, the hydraulic end mill holder is suitable for high-precision machining, while the spring collet end mill holder is more convenient for transportation and installation due to its low cost and portability.


The end mill holder is a critical component that mounts the cutting end mill on the machine spindle for machining. Different end mill holder types utilize various locking mechanisms for this purpose, mainly including spring collet chucks, shrink-fit end mill holders, and hydraulic chucks.

Each end mill holder type has its own advantages in performance and applications. For example, spring collet end mill holders are inexpensive and convenient but have lower rigidity, while shrink-fit end mill holders have good rigidity but complex operations, and hydraulic chucks have the highest rigidity and accuracy but at a higher cost.

Correct selection and installation of the end mill holder is a prerequisite for ensuring machining quality on machine end mills. The suitable end mill holder model should be chosen according to the workpiece material and machining process, and properly installed and commissioned according to procedures.

Additionally, periodic end mill holder inspection and maintenance is also important, such as filter cleaning, checking hydraulic oil, etc., which can extend end mill holder life and improve reliability.

In summary, proficiency in end mill holder knowledge is very important for machine maintenance engineers. Proper application of various end mill holder techniques can effectively improve machining efficiency and quality levels on machine end mills.

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