...back to the coolant articles
Metalworking coolants are a central part of modern machining. Around 90 % of all CNC machines run with coolant — to carry heat away, reduce friction, extend tool life and protect the workpiece from corrosion. Only a small share of machining runs dry, often supported by compressed air.
Coolant removes heat, provides lubrication and chip flushing, stabilises the process and helps hold dimensional accuracy and surface finish. This article gives a practical overview of the main types of metalworking fluid and shows where each category belongs in CNC machining. To pick the right one it helps to understand the two main families and the chemistry behind water-miscible coolants.
Quick links: Main families | Neat oils | Water-miscible coolants | Comparison | Grinding | FAQ
Metalworking fluids fall into two large families: neat (non-water-miscible) oils and water-miscible coolants, which form an emulsion or a solution.
Both families have their own typical applications and strengths, depending on the operation and the material. In practice the decision comes down to the balance between cooling and lubrication, and to how much tank maintenance you are prepared to do.
Neat cutting, grinding and forming oils do not mix with water. They are pure mineral oils, plant-based ester oils or synthetic oils, and they are used wherever maximum lubrication is needed — gear cutting, broaching, deep-hole drilling, Swiss-type machining or precision grinding. A special case is the dielectric fluid for EDM used in electrical discharge machining.
These oils offer very high lubricity, a good surface finish and stable viscosity, but limited cooling. They also generate oil mist, so they need proper extraction and correct disposal.
Modern CNC machines run mostly on water-miscible coolant. It is normally mixed at 3 to 15 % concentrate in water and forms an emulsion or a solution. The advantage is the split of duties: water does the cooling, the concentrate provides lubrication, corrosion protection and stability.
Water-miscible coolants are today's standard because they combine good cooling with acceptable lubrication, cost relatively little and keep the working environment cleaner. To understand why they behave so differently from one another, it is worth looking inside the concentrate.
A coolant concentrate is not a simple "oil and water mixture" but a designed system of several components that together decide how it performs:
The foundation is the base oil — mineral oil, ester oil, synthetic oils (PAO, PAG) or polymers such as glycol. The base oil largely determines lubricity, behaviour in the mixing water and compatibility with different materials.
Emulsifiers keep finely dispersed oil droplets stable in water. They influence emulsion fineness, the tendency to foam and separation stability. Corrosion inhibitors protect the machine, the chips and the workpiece from rust. EP and AW additives (Extreme Pressure / Anti Wear) matter on tough materials such as stainless steel and titanium. Further components improve bio-stability, reduce foaming and extend the service life of the emulsion.
Consider how much the quality of the base oil, the additives and the laboratory behind the formulation affects the result — let alone the quality of the water you later mix it with. Water quality and correct mixing are covered in our article "Mixing coolant and water quality".
Water-miscible coolants divide roughly into five categories. Each has its typical strengths and limits, depending on material and operation.
Semi-synthetic coolants contain roughly 5 to 49 % mineral oil in the concentrate and combine good cooling with solid lubrication. They form a stable, usually low-foaming emulsion and suit a wide range of materials.
In practice they cover a very broad field: turning, milling, drilling and grinding of steel, cast iron and many aluminium alloys can all be handled safely with a well-chosen semi-synthetic product. Resistance to bacterial growth and service life in the tank are usually very good.
Within the EASYCUT range this group is built as a series with a growing material range. BASE201 covers cast iron and unalloyed to low-alloy steel. UNI301 adds stainless steel and a large part of the aluminium alloys, and is the value choice when aluminium is not the main job. PRO302 matches UNI301 and is additionally tuned for aluminium — the choice as soon as aluminium sets the pace. For heavy cutting with a high lubrication demand there is BVR301, also semi-synthetic.
Ester-based coolants use plant-derived ester oils as the lubricating component. They combine very good lubricity with strong cooling and clean machining behaviour. They are particularly interesting for demanding aluminium work, or where sustainability carries weight.
In many cases they raise tool life and improve surfaces while reducing the burden on the environment and on the people in the shop. The drawback is price: ester products sit well above semi-synthetics, and in practice that gap decides more often than the technology does. The example in the EASYCUT range is VEG001.
Mineral-oil-rich emulsions usually contain 50 to 80 % mineral oil in the concentrate. They were the standard for a long time but are steadily losing ground. They do offer good lubricity and a low price per litre, but they are weak on cooling, stability and cleanliness.
The emulsion is more prone to bacterial growth, flushing is limited, and aluminium can darken. The working environment also gets dirtier. CNCmarket.de therefore does not offer classic mineral-oil-rich emulsions.
Synthetic coolants contain no mineral oil. The base is water with polymers and additives. They stand out for very good cooling, good flushing and high resistance to bacterial growth.
Typical applications are grinding operations and machining with a very high cooling demand. Lubricity is lower, corrosion protection is more sensitive and aluminium can discolour. Synthetics also react sharply to the wrong concentration, which makes regular refractometer checks mandatory.
Polymer-based coolants use polymers such as glycol as their base and also contain no mineral oil. They offer excellent cooling, good lubricity and very high stability. Residues on workpieces and machine surfaces are minimal.
They suit plastics, composites and applications that demand an extremely clean surface and very stable emulsion behaviour. The price is usually at the upper end, and they assume good water quality and filtration.
The table below summarises the main properties of each type. The star ratings are a rough orientation from a practical point of view:
| Type | Cooling | Lubrication | Stability | Foam | Material compatibility | Cost |
|---|---|---|---|---|---|---|
| Semi-synthetic | ★★★★☆ | ★★★★☆ | ★★★★★ | ★★★★☆ | ★★★★☆ | ★★★★☆ |
| Ester-based | ★★★★★ | ★★★★★ | ★★★★★ | ★★★★☆ | ★★★★★ | ★★☆☆☆ |
| Mineral-oil-rich | ★★☆☆☆ | ★★★★☆ | ★★☆☆☆ | ★★☆☆☆ | ★★★☆☆ | ★★★★★ |
| Synthetic | ★★★★★ | ★★☆☆☆ | ★★★★☆ | ★★★☆☆ | ★★★☆☆ | ★★★★☆ |
| Polymer-based | ★★★★★ | ★★★★☆ | ★★★★★ | ★★★★★ | ★★★★☆ | ★★☆☆☆ |
The table reads in favour of ester-based coolants — technically, rightly so. What decides in the shop is the column on the right: a semi-synthetic reaches four stars out of five in almost every discipline at a fraction of the price. That is why the large majority of production runs semi-synthetic, and why ester pays off where skin compatibility, disposal or sustainability tip the balance.
Grinding makes different demands than turning and milling, and a coolant that performs on the mill is not automatically the right choice on the grinder.
Heat is generated in a very small contact zone and has to leave quickly — cooling weighs more heavily than lubrication here. That is why grinding often runs on synthetic coolants or on fine-emulsion semi-synthetics. From the EASYCUT range, BASE201 suits grinding on cast iron and steel.
Three points regularly underestimated in grinding:
Setting the concentration and checking it with a refractometer is covered in our article "Mixing coolant and water quality".
The choice depends on your materials, your operations and what your shop is optimising for. In most shops a good semi-synthetic is the right starting point, because it balances cooling, lubrication and stability — and because the value for money is right.
Practical rules of thumb:
Classic mineral-oil-rich emulsions are on the way out and play almost no role in modern CNC environments.
In a shop running mostly steel and cast iron with the occasional aluminium job, EASYCUT UNI301 is the typical all-rounder. The emulsion is stable, low-foaming and works on most machines.
Where the focus is clearly aluminium — series production of housings or profiles, for example — EASYCUT PRO302 is the better choice: the same basis as UNI301, additionally tuned for aluminium. For grinding or lighter work on cast iron and steel, EASYCUT BASE201 is the economical option.
Where cutting is heavy and lubricity matters more than breadth across materials, EASYCUT BVR301 fits. Shops with a strong focus on environment and workplace hygiene can work with the ester-based EASYCUT VEG001, where the budget allows.
If you want to go deeper into water quality and emulsion mixing, we recommend the article "Mixing coolant and water quality". What a coolant actually does in the cut is covered in "The functions of coolant".
You will find coolants for your application in our range:
