LubricantsWhat is soluble cutting oil and what is it used for?
Soluble oil, also called cutting coolant, is the fluid most machine shops use to cool and lubricate while cutting metal. In this guide we explain what soluble oil is, what it is for, how it is prepared and which ones we carry at NAT MAC.
What is soluble cutting oil?
Soluble oil is a concentrate that is mixed with water to form the cutting fluid used in machining. It is also known as cutting coolant, lathe coolant or machining coolant. It is not used straight: it is diluted in water at a set ratio, and that mixture is what bathes the tool and the workpiece while they cut.
The idea is to take the best of both worlds: water cools very well, and oil lubricates and protects against corrosion. Combining them gives a fluid that cools and lubricates at the same time, which is exactly what most machining operations need.
What is soluble oil for?
Soluble oil, once diluted in water, performs several functions at the same time during cutting:
| Function | What does it do? |
|---|---|
| Cools | The water in the mix carries away the heat of cutting and keeps the part from heating up and deforming |
| Lubricates | The oil reduces friction between the tool and the workpiece and extends tool life |
| Evacuates the chip | The coolant flow carries the chips out of the cutting zone |
| Protects against corrosion | Leaves a film that protects the part and the machine components |
How is it prepared? Dilution in water
Soluble oil is prepared by mixing the concentrate with water. There are two key rules to get the mix right:
- Always add the oil to the water, never the water to the oil. If done the other way around, the emulsion breaks and doesn't mix properly.
- Concentration is measured, not eyeballed. It generally runs from 5% to 10% depending on the operation (less for grinding, more for heavy-duty work), and it is checked with an instrument called a refractometer.
If the fluid is too dilute (too little oil), it lubricates poorly, the part rusts and odors appear. If it is too concentrated (too much oil), it foams, leaves residue and you overspend. Checking with a refractometer and keeping the right concentration is what most helps the fluid last and perform well.
Types of soluble oil
Not all soluble oils are the same. Depending on their composition, they fall into three types:
| Type | What is it and what is it for? |
|---|---|
| Soluble (emulsifiable) | They form a milky mixture; they provide good lubrication for medium and heavy-duty work |
| Semi-synthetics (microemulsion) | Finer droplet and translucent appearance; they balance lubrication, cooling, and cleaning |
| Synthetics | With no mineral oil, they are clear solutions; they give maximum cooling and cleaning, ideal for grinding and high speed |
The soluble oils we carry
We carry two lines of CONDAT soluble coolants, covering everything from general machining to the most demanding jobs:
| Product | What is it? | When to use it? |
|---|---|---|
| POLYBIO® | Soluble oil (microemulsion) | General machining and grinding, in various metals |
| MECAGREEN® | Water-soluble coolant of plant origin | Severe machining, aluminum and stainless, with cleaner operation |
Both are supplied as a concentrate and are diluted in water at the ratio recommended for each operation.
Soluble oil or straight cutting oil?
Soluble oil is not the only option. When an operation needs maximum lubrication and the best finish (such as fine tapping or deep-hole drilling), a neat cutting oil, used straight, is sometimes the better choice. We explain the difference between the two in detail in our article straight cutting oil vs soluble oil.
In summary
- Soluble oil is a concentrate that is mixed with water to form the cutting coolant
- It cools, lubricates, clears chips and protects the part during machining
- Prepared by adding the oil to the water and checking the concentration with a refractometer (typically 5% to 10%)
- There are soluble, semi-synthetic, and synthetic types; we carry POLYBIO and MECAGREEN
Why buy your soluble oil at NAT MAC?
We are a CONDAT distributor with more than 54 years of experience in the industry and ISO 9001 certified quality. We don't just supply the coolant: we analyze your machining process and help you define the right product, dilution and maintenance.
- CONDAT soluble oils: POLYBIO and MECAGREEN
- Advice on choosing the right coolant for your operation and material
- Support in defining the fluid concentration and maintenance
- Assessment of your machining process
- Backed by ISO 9001 certified quality
Tell us about your machining process and the parts you produce, and we will recommend the right soluble oil. Request your free quote.
Sources: NAT MAC Lubricants catalog; CONDAT Lubricants.
