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Air-Cooled or Water-Cooled … Which Is Better?

June 2, 2021
High-speed rotation is necessary for high-performance milling, drilling, and other machining operations – but maintaining that performance requires a shop to make a critical decision.

A spindle is the key component of any CNC router, which operators use to perform high-speed milling, drilling, engraving, and other such operations on their benchtop CNC mill. However, as the electric spindle rotates at a high speed to deliver such results, it needs to be cooled down to maintain performance. Ignoring this issue can lead to grave consequences for the machine shop and the specific CNC machine -- from decreased service life to complete burnout of the component.

Air cooling and water cooling are two of the most common cooling systems that come to play in such situations. But which of these techniques is more efficient and effective? And which one should you choose? Let’s analyze.

A head-to-head comparison

The following is a list of some key factors that differentiate air-cooled spindles from water-cooled spindles. Keep reading to find out which spindle is the right fit for you.

Cooling effect. As the name indicates, the air-cooled CNC spindle makes use of a fan that emits air, which functions as a fluid to dissipate heat. Similarly, the water-cooled CNC spindle uses water circulation to cool down the spindle.

Water-cooled spindles are found to be more effective in temperature regulation as their temperature does not typically exceed 40 degrees after water circulation.

Maximum rotational speed. An air-cooled spindle can clock a rotational speed of 18,000 rpm. In contrast, a water-cooled spindle operates at 24,000 RPM. As a result, water-cooled spindles can achieve the task in a shorter time.

Noise generation. Due to the operation of the cooling fans, air-cooled spindles can generate a lot of noise. In contrast, water-cooled spindles offer noiseless operation.

Convenience. Since air-cooled spindles do not come equipped with water tanks or pumping machinery, they are more convenient to use, set up, and preload than water-cooled spindles.

Cutting performance. Air cooling offers greater torque, which contributes to a powerful cutting force. This feature makes an air-cooled spindle better than the performance of a water-cooled spindle.

Durability. The service life of a water-cooled spindle is longer than that of the air-cooled spindle - provided that the operator takes adequate care to maintain it. With routine maintenance activities, such as changing water, using an industrial water cooler, etc., you can extend the CNC machine’s service life.

Accuracy. Water-cooled spindles deliver greater accuracy, with axial and radial runout being less than 0.003 mm. Unfortunately, an air-cooled spindle misses the mark, quite literally, in offering such a high level of accuracy.

Operating environment. The water-cooling method faces two main obstacles with regard to the work environment. First, a water-cooled spindle requires a continuous water supply, pump, and other such equipment. Due to this requirement, it tends to occupy more space.

Secondly, a water-cooled spindle cannot offer optimal performance in climatic extremes, especially when the temperature drops.

On the other hand, air-cooled spindles are less restrictive and can be used in most locations regardless of external factors.

Continued work time. Water cooling would be more suitable than air cooling for cutting and engraving projects that will run for longer durations. This is because water-cooling spindles operate at very high speeds while maintaining a maximum temperature of 40 degrees after every watering cycle.

Price. Air-cooled spindles that offer performance comparable to that of water-cooled spindles are often more expensive. The ease of operability and the fact that an air-cooled spindle could work in all environments are a few other factors that drive up the cost of the equipment.

Best practices for air-cooled spindles

These are a few tips on maintaining your air-cooled spindle:
•  Ensure that the air entering the electric air-cooled spindle is clean and dry.
•  Operators must oil seal the main shaft when the air-cooled spindle is not in use.

Best Practices for water-cooled spindles

Here are a few tips on maintaining your water-cooled spindle:
•  Be sure to change the cooling water often.
•  Frequently clean the water tank, pipes, inlet/outlet, and other elements through which the water passes to remove any blockages.
•  Seal the spindle using oil as a lubricant if it will be out of action for a considerable period.
•  Assess the water quality at the site and set up filtration or water softening units, as necessary.
•  Ideally, water-cooled spindles should operate in ambient temperatures. However, avoid running it when the temperature plunges below zero degrees.
•  After the job is complete, drain all the water out of the system.

Due to the many advantages of a water-cooled spindle, as listed above, it would be prudent to use it for various applications, such as 4-axis CNC routers, multi-head CNC router machines, or any other equipment having multiple rotational axes. However, one must also consider factors like the local temperature and space availability to assess if a water-cooled spindle is a good fit. If such considerations change the evaluation, you can expand your budget to accommodate an air-cooled spindle instead!

Peter Jacobs is the Senior Director of Marketing at CNC Masters -- a supplier of CNC mills, milling machines, and CNC lathes.

About the Author

Peter Jacobs | Senior Director of Marketing

Peter Jacobs is the Senior Director of Marketing at CNC Masters -- a supplier of CNC mills, milling machines, and CNC lathes, from tabletop CNC milling machines to the classic Bridgeport-type vertical mill. He is actively involved in manufacturing processes and regularly contributes his insights for various blogs in CNC machining, 3D printing, rapid tooling, injection molding, metal casting, and manufacturing in general.