This page was updated March 3, 2023

Not sure if water-based lathe coolants are right for your shop? Dive into our primer on fluid coolants.

Anyone who’s gone home at night reeking of sulfur-based oil after a long day of manufacturing parts on machines is thankful for the development of water-based cutting fluids or coolant. But are they as effective as so-called “neat” oils? And considering the variety of coolant options available today, how do you know that you have the right one, or that it’s mixed properly for your particular application? This article offers some guidance on each of these questions, starting with a primer on what to look for in water-based cutting fluids.

Most Swiss-style screw machines continue to use straight oil, as do gear hobs, broaches and hones, gun drills, and other challenging machining operations. But virtually all CNC machining centers and lathes today are designed to use water-based fluids, and for good reason: Properly maintained coolant is far more pleasant to work with. It also does a better job of removing heat than oil, especially when machining aluminum and other nonferrous alloys, and in most cases, is just as effective a lubricant.

Machine Lubrication and Coolant Types

Depending on how much oil they contain before dilution, coolants are placed into one of three, sometimes overlapping categories: soluble oils, synthetic and semisynthetic fluids.

Soluble Oils

The most common of all water-soluble cutting fluids, soluble oils (also known as emulsifiable cutting fluids) are typically 50 percent oil before dilution. When mixed with water, they form a milky emulsion that is an excellent choice for general purpose machining. They are, however, prone to “Monday morning stink”—a foul-smelling odor from microbiological growth of fungus and bacteria that can grow in your coolant sump if not properly maintained.

Synthetic Fluids

As you can probably guess from the name, synthetics contain no oil, using various polymers and chemical compounds to replicate oil’s natural lubricity. They reject tramp oil, so they tend to be the cleanest of all cutting fluids but are often the least lubricious. They are commonly used in grinding applications, but proponents suggest that synthetics can be tailored to virtually any metalworking operation.

Semisynthetic Fluids

The best of both worlds, semisynthetics contain less oil than emulsion-based fluids and are therefore “less stinky,” but they retain many of the same lubricating attributes, making them suitable for a broader range of work compared with straight synthetics.

Machine Lubrication with Water-Based Fluids

Many oil-based fluids have been replaced by vegetable oils and water-soluble cutting fluids. All coolants, however, contain additives that enhance lubricity, inhibit rust and (most) bacteria growth, or reduce foaming. Additives react favorably during machining to provide additional lubricity in the cut. Among the most important are “extreme pressure” additives, commonly known as EP, and include chlorine, sulfur and phosphorus.

Whatever fluid path you take, be sure to follow the manufacturer’s mixing recommendations, because more coolant is definitely not better. The water itself—which makes up roughly 90 percent of any cutting fluid—is also important. If you’re not willing to drink your tap water, neither is your machine. Invest in a reverse osmosis system, as well as a water softener if hardness is a problem. Also, install a tramp skimmer on each machine tool, and use a refractometer to keep a regular eye on fluid concentration.

How to Apply Water-Based Fluids and HPC to Cutting

The way in which you apply a cutting fluid is nearly as important as which one you’re using, and in some cases, even more so. Nearly all CNC lathes and most machining centers have a through-the-tool coolant capability—so use it, even if that means investing in new toolholders and cutter bodies.

And if your machine is capable of high-pressure coolant, invest in a system and get pumping. HPC improves tool life, allows increased feeds and speeds, and largely eliminates problems with chip control—unless you cut easy material like brass or 12L14 steel all day, you’re doing your shop a disfavor without it. Pump pressures of 1,000 psi are common, although even a few hundred pounds is better than the lackadaisical pressure that comes standard with most machine tools.

The way in which you apply a cutting fluid is nearly as important as which one you’re using, and in some cases, even more so.

Many machine operators notice an uptick in tool life after changing their cutting fluids. There’s a reason for this: Clean fluid is free of the microscopic bits of metal and dirt that add to tool wear. And while you certainly can’t change cutting fluids every week, you can filter them, which is nearly as effective.

Synthetics may require a deeper investment than soluble fluids, but cost should not be the deciding factor. The most important thing to consider when it comes to cutting fluids is this: If productivity suffers as a result of the wrong cutting fluid, then that may require a new strategy. Invest in what’s best for machine throughput. As always, fluids should be kept clean and well-maintained, so you’ll also need to have a quality sump pump.

Comparing Water-Based Lathe Coolants

Soluble Oils

  • Oil composition: 50 percent oil before dilution
  • Lubricity: High
  • Bacterial growth: High
  • Applications: General purpose machining

Synthetic Fluids

  • Oil composition: None
  • Lubricity: Low
  • Bacterial growth: Low
  • Applications: Grinding

Semisynthetic Fluids

  • Oil composition: Usually 5 to 35 percent before dilution
  • Lubricity: Moderate
  • Bacterial growth: Moderate
  • Applications: Broad range

Frequently Asked Questions

Is CNC machine coolant toxic?

Cutting fluids contain chemical additives that can cause skin irritation, rashes and dermatitis. As the fluid gets dirty with bacteria, fungi and metal chips, the chances of skin and lung irritation increase.

Why does CNC coolant stink?

When soluble oils are mixed with water, microbiological growth of fungi and bacteria can grow in the coolant sump if not properly maintained, causing a foul-smelling odor.

What kills bacteria in CNC coolant?

Cutting fluids should have a pH of around 8.6 or higher to inhibit bacterial growth and prevent corrosion of metal surfaces. Monitor pH with a meter or test strips weekly. If pH gets low, use a pH adjuster to raise the pH of the fluid, or replace the cutting fluid.

What do you do with old CNC coolant?

When CNC coolant becomes too dirty or loses its effectiveness, it should be collected from the sump and disposed of according to local regulations for dangerous waste. Metalworking fluids can also be recycled, either by hiring a company to do it or purchasing specialized equipment to have at the facility.

How do I stop my CNC coolant from foaming?

Foaming can be caused by a variety of factors, including a leak in piping or hoses and high coolant pressure, and is more pronounced in fresh coolant. Many coolants contain additives that reduce foaming, and the additives may need to be replenished later.

Quick Poll: Metalworking Fluids

Which steps does your business use most often to optimize water-based machining tool coolants?

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Informative , thank you !


Thank you for your feedback & for visiting Better MRO.


Thanks for better consultant that I have been applicate


how to making & formula for

*Emulsion Fluid for Metal, non-Ferrous Metal


* Semisynthetic Fluid


I’ve recently been put in total charge of a Mazak Mazatrol 640M, and it seems the prior operator were working on a very basic level of understanding when it came to this machine not only on the operating side but also the day to day maintenance side. Have you got any type of advice or insight on which type of cutting fluid I should get the company to get from now on, the older stuff they’ve got isn’t exactly up to par.


Hi Jeremy,

Always be sure to check your machine manual for the recommended type of coolant, as there are so many makers of machines. One of the best coolants would be Master Fluid Solutions Trim MicroSol 585XT, (cutting & grinding fluid semisynthetic for machining Part # 72761778 on Though again, please make sure to check your machine manual for compatibility.

Also, Jeremy, if you want/need to further discuss machining, you can always check out our Better MRO forum as well:

Hope that helps, and thanks for visiting Better MRO.


Looking for a good soluble cutting fluid to use on CNC millers, can you recommend. I currently use ECOCOOL MM. Would you recommend this??


TRIM® E206 is a soluble oil (emulsion) coolant that performs extremely well in a wide range of machining operations on both ferrous and nonferrous materials. It has the lubricity necessary for heavy-duty machining center work and still provide the wetting and cooling necessary for high-speed turning and grinding operations. Extremely stable emulsion to reduce carry-off and to facilitate getting the fluid to the point of cut. Leaves a soft fluid film to prevent sticky ways, chucks, tool holders, and fixtures. Coolant residue is easily removed with water, working solution, or aqueous cleaners.
E206 especially for: Applications — band sawing, centerless grinding, drilling, gear hobbing, heavy-duty broaching, heavy-duty machining center work, high-speed turning, in-feed centerless grinding, internal grinding, plain grinding, production grinding, reaming, roll threading, surface grinding, surface milling, tapping, thread forming, and turning.
Metals — 6000 series aluminum, aerospace aluminum alloys, brass, bronze, cast aluminum, copper, exotic alloys, ferrous metals, heat-treated steel, high-carbon steel, high-nickel alloys, nonferrous metals, stainless steels, steels, titanium, tool steels, wrought aluminum, and yellow metals.
Concentrations of 7% or higher provide the best sump life.
Use mineral-free water to improve sump life and corrosion inhibition while reducing carry-off and concentrate usage.
MSC stocks E206:
1-gallon size 01790781
5-gallon size 01790799
54-gallon size 84777192

Always consult your machinery manual to guarantee that you're using the correct fluids.

To help ensure the best possible working solution, add the required amount of concentrate to the required amount of water (never the reverse) and stir until uniformly mixed.


What's that ringing? Oh, it's the phone. 1991 is calling and wants it's coolant back.


hi sorry to trouble you but could you please help, my husband has brought 1 lt of coolent for his lathe and on the bottle it says 5 0/0 nothing else we are in our 70 and we cant work it out is it 5 0/0 coolent to how much water i have e mailed the person who we got it from but all he has said is 50mil but not how much is that to water we may be old but just cant get any where.


We are using tsugami b0386-III swiss machines and using blasomill straight oil for cutting a286. Would a synthetic/soluable coolant be better?


Hi James,

This would be a great question to take to our metalworking forum:

Creating a login is easy, just click on the “Register” button. 


Hi sir,

we have swiss type machine to process a stainless stell s316, however our machine operator switch the coolant from neat oil to water based coolant and it caused the component result into rejection.  Can the water based coolant really actually change the material structure ( we used stainless steel ) ....? 


While the water based coolant can't actually "change" the material structure, the material may react differently to the way it is being machined. You don't mention exactly what happened but since it's 316SS, I would imagine that the material "work hardened" during the machining process. 316 is very susceptible to this and since water based coolants are so much more effective at cooling, it is more of an issue. That said, water based coolants are still absolutely recommended for stainless in most applications. In order to combat work hardening, you want to avoid things like very light cuts, spring passes, peck drilling, and dwell. Making sure coolant is flowing right to the point of cut is critical to help keep the stainless from heating up in the first place. Coolant-thru tooling is a great way to accomplish this. 


Thanks for the tip that there are machine fluids I can use that can be a bit odorless. I will make sure to look for something like that when hiring machine shop services. I'm going to need to have some parts produced for my car restoration project because I can't seem to find them in any store I go to.


Looking for BeckerLube S100 or equivalent.


I'm not even sure if Becker Lubricants are available in the US. You might want to try Lubriplate ISO-100 Vacuum Pump Oil as a replacement.


Is there any particular way to assess the correct concentration to used based on application e.g. turning, milling, drilling and based on the metal being cut?


Look for the data sheet from the manufacturer of the coolant that you are using. That will generally give you the proper concentration ratios for different applications. Then use a refractometer each day to make sure your coolant is at the right concentration. (Remember that synthetic and semi-synthetic coolants do not read directly. The manufacturer's data sheet will give you a 'refractometer factor' so that you can figure out what the concentration is in your sump.)



I use Hocut MPB 795 semi synthetic coolant on cnc lathe and mills. It's a bobbing shop, hence I machine Stainless steel,  Aluminum alloys,  and carbon steel. Problem I have is everyday morning, I find  rusted spots at many places looks likes a dump. It's only at some spots, looking forward to your expert advice,  to fix this problem. 

Many Thanks.  Lax.



The MBP 795 has a very high corrosion protection level. There could be 2 possible problems causing rust spots. The first is that the product in the system may have been recharged to many times and is not accepting the make up additions and mixing correctly. The second is that the concentration level is too low and when the water evaporates over the night it is leaving a thin residue and causing the rust spots. Keeping the correct concentration should stop this situation. The reading on a refractometer should be 5-7% for medium and 7-10% for heavy duty machining.


Always remember (OIL) oil in last. Put water in a bucket and add the concentrate to the water then mix and then put in the coolant tank. Check the tank concentration with a refractometer and adjust accordingly.

If there is anything else we can help with please post in our METALWORKING forum again!


Dear Team, 

we atre facing some pitting issues on the Alluminium alloys (2219) and we have releted this topic to the coolant liquid.

What is your suggestion on the right colling lubrivat for such alloy (AA2219). There are some guidelines in the maintainance of the coolant? time/frequency to change it, PH, batteriological level, etcc.

Thankyou for your suggestions.

Very thank




You don't say what your application is (turning, milling, tapping, etc.) and that would effect what we might suggest for you. In general, look for fluids that explicitly state that they are compatible with aluminum. With good housekeeping practices, your fluid should have at least a 6 month sump life. It is important to check your fluid's concentration at least once per day and add a make-up solution as needed. Be sure to skim the tramp oils on a regular basis (typically once per week in a still sump) to help keep bacteria at bay. When changing your fluid, be sure to run a cleaning product (like Master Fluid Solutions' Whamex) that will clean all the coolant lines before dumping the old fluid. Wash down and rinse the machine then start with clean, properly mixed fluid. 


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