Cool Down With the Right Coolant

cool down your cnc mill using the right coolant

Manufacturing with a 3 axis milling machine creates parts and components, and it generates heat. Without the correct coolant, machines break down, and prior to that happening, product quality suffers.

Check the Levels Before Every Job

Familiarize yourself with each machine’s coolant gauge. Most CNC machines have a coolant tank, which sits inside a housing. A floating gauge monitors the amount of coolant in the tank and connects to the machine controls via a cable.

Understand the Correct Coolant for Your Machine

Generally, most machines, such as a lathe or a 3 axis CNC mill, use one of the following types of coolant:

  • Emulsions: oils suspended in water, often with added emulsifiers that keep the solution mixed
  • Chemical coolants: pre-concentrated emulsions with little oil that mix easily with water
  • Semi-chemical Coolants: chemical fluids and an emulsion that have low oil content.
  • Straight Cutting Oils: not mixed into water, characterized as active or inactive, generally based upon their sulfur content
  • Gasses: compressed air or inert gasses
  • Paste and Solid Lubricants: wax, paste, and soap[1]

Never use water as a coolant by itself, because without the additives of coolant fluid, the water promotes rusting and other corrosion.

Know the Right Recipe for Machine Coolant

Most machine manufacturers provide very explicit instructions on the type of coolant their machine requires. For instance, the manufacturer of a 3 axis CNC milling machine will provide detailed data on not only the type of coolant required, but also the concentration level of the coolant.

Pay attention to the proportions they state and only use deionized water when mixing a coolant solution, since deionized water is generally non-corrosive on metals such as aluminum and steel.

Monitor Coolant Quality Constantly

Coolant fluids become contaminated over time by various substances. A refractometer (a small, portable instrument that reads the concentration of water-soluble fluids) gives a quick and accurate reading of coolant concentration levels. Most manufacturers recommend testing coolant for other foreign substances such as bacteria and fungi. If an additive for controlling bacteria is required, be sure it is compatible with the machine. The machine monitoring process should also include a weekly cleaning of catch pans, and a regular cleaning of the tank to remove any buildup of sediment.

Coolant Variations by Material Milled

Understanding the correct coolant for the type of job and material used results in higher productivity efficiency and sustained high quality products. Recommendations vary according to manufacturer, but as a general idea of different coolants used for different materials in a grinding project, consider this chart from Fox Valley Technical College:

Material Milling Drilling Tapping Turning
Aluminum Soluble oil (96% water) or mineral oil Soluble oil (70-90% water) 25% sulfur-based oil mixed with mineral oil Mineral oil with 10% fat (or) soluble oil
Brass Soluble oil (96% water) Soluble oil 10-20% lard oil with mineral oil Mineral oil with 10% fat
Bronze Soluble oil Soluble oil 30% lard with mineral oil Soluble oil
Alloy Steels 10% lard oil with 90% mineral oil Soluble oil 30% lard oil with 70% mineral oil 25% sulfur base oil with 75% mineral oil
Cast Iron Dry Dry Dry or 25% lard oil with 80% mineral oil Dry
Malleable Iron Soluble oil Soluble oil Soluble oil Soluble oil
Copper Soluble oil Soluble oil Soluble oil Soluble oil
Low Carbon and Tool Steels Soluble oil Soluble oil 25-40% lard oil with mineral oil 25% lard oil with 75% mineral oil


Using the right coolant for the job not only extends the life of the machine but also improves the quality of the products created. As with so many “preventative” measures, people often dismiss its importance. However, taking the time to monitor coolant fluids saves a lot of money over time.