How to Choose the Right Cutting Fluid for Your Material

Choosing the right cutting fluid (soluble coolant) is one of the most important decisions in any machining workshop. A poor choice can lead to poor surface finish, premature tool wear, workpiece corrosion or health issues for operators.

In this guide we explain the key criteria to select the right cutting fluid for your application.

What types of cutting fluid are available?

Semi-synthetic cutting fluids

Contain a blend of mineral oil and synthetic components. They are the most versatile option: good lubrication, acceptable cooling and balanced cost. The most common choice in workshops machining steel and cast iron.

Synthetic cutting fluids

Contain no mineral oil. They offer the best cooling and cleanliness, with longer service life. Ideal for grinding and high-speed operations where heat evacuation is critical.

Vegetable-based cutting fluids

Formulated with vegetable esters instead of mineral oil. More environmentally friendly and safer for operators. Excellent lubrication, ideal for aluminium and non-ferrous materials.

How to choose based on your material?

Carbon steel and alloy steel

For general turning, milling and drilling in steel, a semi-synthetic cutting fluid at 6-8% concentration is the most reliable choice. Look for EP (extreme pressure) additives for severe operations like threading or broaching.

Aluminium and light alloys

Aluminium is particularly sensitive to staining. You need a cutting fluid with controlled pH (8.5-9.0), chlorine-free and without active sulphur. Vegetable-based or synthetic formulations give the best results.

Grey and nodular cast iron

Cast iron generates short chips and abrasive dust. You need a cutting fluid with good settling and filtration properties. Low-foam semi-synthetics work well. Recommended concentration: 5-7%.

Stainless steel and superalloys

High-hardness materials that generate significant heat. Maximum EP lubrication is required. Use semi-synthetic EP cutting fluids at 8-10%, or even neat cutting oil for very severe operations.

What concentration should I use?

• Grinding: 3-5%
• General turning and milling: 5-8%
• Deep hole drilling: 8-10%
• Threading and broaching: 8-12%

Correct emulsion preparation

A very common mistake is adding water to the concentrate. Always add concentrate to water, stirring constantly. Doing it the other way round creates lumps that don't dissolve and shorten bath life.

For large preparations, a MIXTRON proportional dosing pump automates mixing at the exact concentration, eliminating human error.

Preventive maintenance: the key to longevity

1. Check concentration weekly with a refractometer
2. Measure pH: maintain between 8.5 and 9.2
3. Remove tramp oil with a skimmer
4. Aerate the sump during long stops (weekends, holidays)
5. Filter to remove metal particles and dirt