How to Choose the Right Spindle for Your CNC Machine

The spindle is the heart of a CNC machine. It determines maximum rpm, rigidity, and suitability for materials.

A cartridge spindle is what most DIY CNC builders choose, as they are easier to use off-the-shelf tool holders. They also usually have a common taper so that you can test them with a dial indicator.


If you’re looking for a suitable CNC spindle from companies like, it’s essential to evaluate its power capacity to meet your requirements. This can help you avoid thermal errors that may lead to part defects or machine failure. A powerful spindle can remove more material per minute than a less-powered one.

A high-powered spindle also can accommodate different types of tools, which makes it a good choice for your project requirements. However, you should keep in mind that the type of tool you use will influence the speed requirements of your spindle. Carbide tools, for example, require higher RPMs than HSS tools. Some tools also have special coatings that must be activated at specific speed ranges.

It would help if you also considered the wattage of your workshop. Most spindles need 220 volts to operate, and ensuring that the workshop can provide enough wattage to support them is important.

Lastly, you should ensure that the spindle matches the workpiece materials you will be using it on. For instance, you’ll need a more powerful spindle with hard materials like steel. A weaker spindle could cause the blade to slip and damage your workpiece. You can test the drawbar force of your spindle by using a hydraulic, battery-less dial indicator.


Many machinists quickly blame their tools for machining times, but your spindle also has a significant impact. When a spindle isn’t running at the right speed, it can slow down your operation or cause unnecessary wear and tear on the tool.

The speed of your spindle determines how quickly the material is removed and what kind of finish it will have. Large-diameter tools typically require lower speeds to achieve a good finish, while smaller-diameter tools can work at higher speeds.

Choosing the right speed for your CNC machine can help you cut materials more efficiently and reduce cycle times. You can test your spindle’s speed using a dial indicator (with the machine turned off). First, place the point of the indicator on the shaft and turn it to find the highest or lowest point. Record this value. Then, compare it with the number indicated on your tachometer.

Depending on your machine’s setup, it may be possible to monitor the spindle’s speed automatically. If this isn’t an option, use a non-contact displacement sensor to measure runout. These sensors track displacements with laser triangulation and are quick to use. To ensure accurate results, you must use a clean environment for testing. Floor vibration, acoustic noise, and contaminants can all affect the measurement and lead to inaccurate test results.

Feed Rate

A tool’s diameter determines how much material it cuts in a single spindle revolution. This is why a larger tool can complete a cutting operation in less time than a smaller one, even when rotating at the same speed.

The cutter type also determines the rate at which the tool removes the material. For example, a solid carbide endmill can have an extremely narrow flute and still cut the same material as a wider fluted endmill. It is important to choose the right cutter for your specific job.

Feed rate is a function of the tool diameter, the type of material you are working with, and your spindle’s RPM. It is calculated as a product of a formula using the following variables:

You can experiment with various combinations of these factors to find the “sweet spot” for your machining. Depending on your goals, you can maximize material removal rates, surface finish, or tool life within this envelope.

To achieve a better surface finish, you can reduce your feed rate and keep the spindle RPM the same. However, if you reduce your feed rate while the spindle is spinning, you will begin to rub the workpiece against the tool, which can cause heat and decrease lifespan. You can avoid this by choosing a tool with a wide enough flute that you do not have to cut as deeply in each pass.


One of the most important factors in determining how well your CNC machine cuts is the precision of the spindle. High precision can help reduce tool damage and improve the quality of your finished parts.

The type of material you will be cutting also plays a role in choosing the right spindle. Different materials have varying hardness and intrinsic characteristics, requiring a specific approach to cut them effectively. It would help if you chose a spindle with the RPM, power, and cooling capabilities required for your materials.

For example, if you’re machining wood, you’ll need a spindle with 24,000 rpm and 1kW of power. However, if you’re cutting steel, you’ll need a higher RPM (up to 24,000) and more power (5-6 kW).

Your spindle must be compatible with the tools you plan to use. Different tools have taper and gripper grooves, so make sure your spindle is compatible.

The size of the spindle will influence its ability to handle large loads. Choosing a larger spindle will allow you to machine thicker materials, while a smaller one is best for lighter-duty applications.

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