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How to Check and Adjust Your Coolant Mixture

Check and Adjust the Coolant Mixture for Optimal CNC Machining Performance

Ensuring the correct ratio of coolant concentrate to water is crucial for the efficient operation of CNC machines. A proper coolant mixture not only enhances machining performance but also extends the life of your tools and workpieces. An incorrect mixture, on the other hand, can lead to a range of issues, including loss of anti-foaming properties, reduced lubrication, and increased wear and tear on machinery.

Why the Right Coolant Mixture Matters

Coolants play a vital role in CNC machining by reducing heat, minimizing friction, and removing chips from the cutting area. The right balance between coolant concentrate and water is essential to maintain these benefits. A mixture that is too concentrated or too diluted can compromise the effectiveness of the coolant, leading to potential damage and decreased performance.

How to Check and Adjust the Coolant Mixture

1. Follow Manufacturer’s Recommendations

Always adhere to the manufacturer’s guidelines for mixing coolant concentrate with water. These recommendations are designed to ensure the optimal performance of both the coolant and your CNC machine.

2. Use a Refractometer

A refractometer is an essential tool for accurately measuring the concentration of your coolant mixture. Here’s how to use it:

  1. Calibrate the Refractometer: Before taking any measurements, calibrate your refractometer using distilled water. Place a few drops of distilled water on the prism, close the cover, and adjust the calibration screw until the scale reads zero.
  2. Measure the Coolant Concentration: Take a sample of the coolant mixture from your CNC machine. Place a few drops on the refractometer’s prism, close the cover, and look through the eyepiece. The reading will indicate the concentration level, which you can compare against the manufacturer’s recommended ratio.
  3. Adjust the Mixture: Based on the reading, adjust the mixture by either adding more coolant concentrate or water. Ensure you mix thoroughly to achieve a homogeneous solution.

3. Mix Slowly to Avoid Introducing Air

When mixing coolant concentrate with water, do it slowly to prevent introducing air into the mixture. Air bubbles can cause foaming, which reduces the effectiveness of the coolant. Here are some tips for mixing:

  1. Pour Water First: Start by pouring the required amount of water into a clean container. This prevents the coolant concentrate from sticking to the bottom and sides of the container.
  2. Add Coolant Concentrate Slowly: Gradually add the coolant concentrate to the water while stirring continuously. This ensures a smooth blend and minimizes the introduction of air bubbles.
  3. Stir Thoroughly: Use a clean stirring tool to mix the coolant concentrate and water until you achieve a uniform solution. Avoid vigorous stirring, as this can introduce air into the mixture.

Tips for Maintaining Optimal Coolant Performance

  • Regularly Monitor Concentration: Periodically check the coolant concentration using a refractometer to ensure it remains within the recommended range.
  • Maintain Cleanliness: Keep the coolant system clean by regularly removing contaminants and replacing filters. This helps maintain the coolant’s effectiveness and prevents clogging.
  • Adjust for Environmental Changes: Environmental factors like temperature and humidity can affect the coolant mixture. Be prepared to adjust the ratio accordingly to maintain optimal performance.


Ensuring the correct ratio of coolant concentrate to water is a critical aspect of CNC machining maintenance. By following the manufacturer’s recommendations, using a refractometer to measure concentration, and mixing the coolant properly, you can maintain the coolant’s effectiveness and extend the life of your tools and machinery. Regular monitoring and adjustment of the coolant mixture will lead to better machining performance, improved surface finish, and reduced downtime.

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