Manufacturing Index

Cutting Fluids


For many machining operations including sawing, drilling, turning, milling and grinding cutting fluids can be used to allow higher cutting speeds to be used, to prolong the cutting tool life, and, to some extent reduce the tool- work surface friction during machining..  The fluid is used as a coolant and also lubricates the cutting surfaces.

The advantages of using cutting fluids are listed below

  • Cools the work surface and tool
  • Lubricates the interface between the work surface and tool
  • Flushes away some dust,chippings, and swarf
  • Reduces tendency for chip adhesion/pressure welding to tool tip
  • May improve resulting surface finish
  • May increase tool life (see below)
  • Allows higher cutting speeds

There are some disadvantages in using cutting fluids as listed below

  • For certain Machine tools- A costly engineering system is required for applying the fluid
  • The fluid used has to be prepared and after use, filtered for re-use of disposed
  • Some fluids have a health risk if not used correctly causing problems such as dermititus
  • Some cutting materials are affected by thermal shock e.g. cemented carbides.   Use of cutting fluids should be avoided for these materials

The vast majority of cutting fluids used are liquids in the form of extended mineral oils and/or synthetic fluids, which emulsify in water.  These fluids can be applied as a pumped flow or via an oil mist using compressed air.  A number of specialised machining operations use injected gases (compressed air or inert gases).   Solid or paste cutting substances are also used which include greases, pastes, waxes, soaps, graphite based substances etc e.g tallow for tapping

Important.. When machining magnesium there is a fire hazard risk if water based cutting fluids are used.  Hot water reacting with magnesium results in the production of hydrogen gas.  Magnesium should be machined dry or with a low acid anhydrous oil /mineral based oil.

Cutting fluids review

Lard Oil is an oil from lard (tallow) is an excellent cutting oil but it is relatively expensive and so it it mostly used in combination with mineral oils.

Mineral oils are used for non-ferrous alloy and free-cutting steels for low duty machining operations.  They are generally extracted from petroleum oil.   This group includes paraffin.

Emulsifiable oil (soluble oil) is produced by adding oil to water forming a milky white solution.  The concentration used depends on the severity of the machining operation.   The more severe the operation the more oil is added in the solution.   The manufacturers recommendation should be used in preparing the fluid

Synthetics (chemical fluids) are solutions of organic and inorganic chemicals dissolved in water.  Plain fluid solutions have reasonable rust inhibition, good cooling and low lubricity and are used for grinding operations.   Other types include additives for surface wetting properties and improved lubrication and EP (extreme pressure) properties.   These are used for a wide range of machining operations

Cutting fluids for machining common metals

  • E = Emulsifiable oil, souluble oil diluted in ratio of 1:5 to 1:50 with water
  • M = Mineral oil-Synthetic or natural based oils
  • ML = Mineral oil- Lard(Tallow) combination
  • P = Paraffin (Kerosene) - Use and store with extreme care
  • S = Synthetics (Chemical cutting fluid)

Material Sawing Drilling Reaming Threading Turning Milling Grinding
Carbon Steel
Mallable Iron
Wrought Iron
Stainless Steels
Tool Steels
Grey Cast Iron Dry, E Dry, E Dry, E Dry, E, ML Dry, E Dry, E, Dry, E,M
Aluminium Alloys Dry,E,M E,M,ML ML,M,E ML,M,E,P E,M,ML,P E,M,ML E
Copper Alloys
Brass, Bronze
Magnesium Alloys Dry,M Dry,M Dry,M Dry,M Dry,M Dry,M Dry,M

Links Providing information on Cutting Tools
  1. Cutting Fluids Page.. A comprehensive review of cutting fluid science
  2. Soluble Cutting Fluids - Supplier Data by - Useful information article
  3. Cutting Fluids...Useful Notes
  4. Selection of Cutting Fluids...An informative downloadable article
  5. Selecting the right cutting and grinding fluids...An informative downloadable article

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