"What should I get for my CNC, a water cooled or air cooled spindle?" While there is no definitive answer on this let's take a look at pro's and con's of both:
The main difference between them?
Air-cooled spindles rely on a shaft driven fan mounted typically to the top of the spindle to flow air down through the core of the spindle in order to keep it cool.
Water-cooled spindles on the other hand use a forced liquid cooling system to flow coolant around the spindle in order to keep it cool during operation.
Water-cooled Spindles
Pro's
✔️ Can be run at very low RPM's and for extended periods of time.
✔️ Is generally quieter than an air-cooled spindle under no load.
✔️ Can be used safely with coolant flood and mist options.
Con's
❌ Generally requires an additional air assist to clear swarf channel.
❌ Complex setup with more parts that can fail. I.e: Water pump failing.
❌ More maintenance is required to ensure safe operation.
❌ Potential electrical safety risk; fluids & electricity.
Air-Cooled Spindles
Pro's
✔️ Do not require complex parts to operate and potentially fail.
✔️ Can act as their own air assist by clearing the swarf channel.
✔️ Can be used safely with coolant flood and mist options.
✔️ Much lower maintenance.
Con's
❌ RPM's generally need to be above 16K RPM for long jobs.
❌ Can pose safety risk if using coolant flood / mist.
❌ Cooling fan on top can clog if covered with swarf.
Some common spindle myths debunked!
MYTH: "Water cooled spindles are quieter than Air cooled spindles"
Water-cooled spindles do indeed operate more silently than Air-cooled spindles under no load. I.e: not cutting anything, just running.
Actually cutting any material of any kind will be substantially louder than the sound of either water or air cooled spindles running with out cutting anything.
Most commonly, the loudest part of using your CNC machine will be the vacuum extraction system used for dust / swarf management.
MYTH: "Air-cooled spindles can't be used for long jobs as they overheat."
Our team and some of our users have run several jobs exceeding hundreds of hours of run time with air-cooled spindles and have had no issues running them. The key here is keeping RPM's nice and high to ensure strong cool airflow through the spindle.
Keeping spindle RPM's over 16K RPM is generally the key here. Most materials and endmills should not be run lower than 16K RPM anyway. The only circumstance where RPM's will likely need to be lower is when using a rather large surfacing cutter. Typically these are run at 12K RPM lower. If your job won't exceed say 1 hour then an air-cooled spindle should still be fine.
MYTH: "Water-cooled spindles circulate their own coolant automatically."
The vast majority of water-cooled spindles on the market do not in fact have the ability to use the Spindles RPMs to pump coolant through the spindle. They mostly require an electronic pump to circulate coolant through the system.
We hope this relatively simple article will help you in your decision making process when deciding which way to go when deciding on the spindle for your CNC.