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Determination of cutting oil concentration with SmartRef Digital Refractometer

Cuttin oil concentration determination with SmartRefWhat is cutting oil?

Cutting oils are metal working fluids that are used as coolants and lubricants for processes like drilling, turning, milling or grinding. The main function of the cutting oil is the sufficient cooling of the contact zone between the tool and the work piece. The proper concentration of cutting oils during machining increases cutting speeds, efficiency, surface quality and reduces cost and power consumption.

A distinction is made between straight oils (non-water miscible) and water miscible cutting fluids (emulsions). The two types differ in their lubricating and cooling properties.

Today, the water-miscible cutting oils are the most commonly used types, due to their good cooling capacity and price. The emulsion is made by mixing the cutting oil concentrate with water to the needed dilution ratio. The typical cutting oil concentration is normally between 4% and 10%. However, the proper concentration depends on the machine and application.


When to measure the cutting oil concentration?

The first concentration measurement should be done when mixing a new cutting oil-water solution. If the dilution is too weak, the cutting oil mixture and used tool might have a shorter lifetime, corrosion protection is insufficient and the lubrication properties are lower. Whereas, if the mixture is too high, the risk of foam-building, and cost increase.

Once the correct dilution ratio is reached, the water-miscible cutting oil concentration needs to be checked frequently because its composition can change during usage. Possible reasons for a concentration change can be bacterial growth, evaporation of water or contamination.


It is important to check the cutting oil concentration to 

  • ensure employee safety.
  • prolong lifetime of machine and tool.
  • prevents corrosion.
  • allow the machine to run at a higher speed.
  • ensure consistent quality of the produced products.
  • save cost.


Measuring procedure of cutting oil concentration with the SmartRef Digital Refractometer:

With our digital refractometer SmartRef and the Lab Meister mobile app, the cutting oil concentration can be measured quickly and reliably. The SmartRef measures the sample in °Brix and applies the user-specific correction factor automatically to the measurement result. The correction factor can be set between 0,5 and 3,0 in the settings.

Cutting oil App Screen

Documentation is one of the most important aspects of monitoring cutting oil concentrations on a regular basis. Using Lab Meister mobile app, measurement results can be saved directly in logs and displayed graphically over time. In this way, the user can quickly identify differences in the cutting oil concentration and decide whether it is time to replace the cutting oil mixture or not.

 Cutting oil graph

It has never been so quick and easy to keep an eye on the concentration of the cutting oil!


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