Editing Cutting fluid (section)

=== Liquids ===
There are generally three types of liquids: mineral, semi-synthetic, and synthetic. Semi-synthetic and synthetic cutting fluids represent attempts to combine the best properties of oil with the best properties of water by suspending emulsified oil in a water base. These properties include: rust inhibition, tolerance of a wide range of water hardness (maintaining pH stability around 9 to 10), ability to work with many metals, resist thermal breakdown, and environmental safety.<ref>OSHA (1999). [http://www.osha.gov/SLTC/metalworkingfluids/metalworkingfluids_manual.html Metalworking Fluids: Safety and Health Best Practices Manual]. Salt Lake City: U.S. Department of Labor, Occupational Safety and Health Administration.</ref>

Water is a good conductor of heat but has drawbacks as a cutting fluid. It boils easily, promotes rusting of machine parts, and does not lubricate well. Therefore, other ingredients are necessary to create an optimal cutting fluid.

[[Mineral oil]]s, which are petroleum-based, first saw use in cutting applications in the late 19th century. These vary from the thick, dark, sulfur-rich cutting oils used in heavy industry to light, clear oils.

Semi-synthetic coolants, also called ''soluble oil'', are an emulsion or [[microemulsion]] of water with mineral oil.   In workshops using British English, soluble oil is colloquially known as '''SUDS'''.<ref>{{Cite web | url=https://www.midlandslubricants.co.uk/metalworking/cutting-oils-suds/midlands-lubricants-general-soluble-cutting-oil-suds/ | title=General Soluble Cutting Oil – Water Soluble Cutting Oil – Midlands Lubricants Ltd| date=16 January 2016}}</ref> These began to see use in the 1930s. A typical CNC machine tool usually uses emulsified coolant, which consists of a small amount of oil emulsified into a larger amount of water through the use of a detergent.

[[Synthetic chemical|Synthetic]] coolants originated in the late 1950s and are usually water-based.

The official technique to measure oil concentration in cutting fluid samples is manual [[titration]]:<ref>{{cite book |doi=10.4324/9781351228213 |title=Metalworking Fluids, Third Edition |date=2017 |isbn=978-1-351-22821-3 |editor-first1=Jerry P. |editor-last1=Byers }}{{pn|date=March 2025}}</ref> 100ml of the fluid under test is titrated with a 0.5M HCl solution to an endpoint of pH 4 and the volume of titrant used to reach the endpoint is used to calculate the oil concentration. This technique is accurate and not affected by fluid contamination, but needs to be performed by trained personnel in a laboratory environment. A hand-held [[refractometer]] is the industrial standard used to determine the mix ratio of water-soluble coolants<ref>{{cite journal |last1=Fukuta |first1=Mitsuhiro |last2=Yanagisawa |first2=Tadashi |last3=Miyamura |first3=Satoshi |last4=Ogi |first4=Yasuhiro |title=Concentration measurement of refrigerant/refrigeration oil mixture by refractive index |journal=International Journal of Refrigeration |date=June 2004 |volume=27 |issue=4 |pages=346–352 |doi=10.1016/j.ijrefrig.2003.12.007 }}</ref> that estimates oil concentration from the sample refractive index measured in the [[Brix scale]]. The refractometer allows for in situ measurements of oil concentration within industrial plants. However, contamination of the sample reduces the accuracy of the measure. Other techniques are used to measure the oil concentration in cutting fluids, such as measure of the fluid [[viscosity]], [[density]], and [[ultrasound]] speed. Other test equipment is used to determine such properties as acidity and conductivity.

Others include:
* [[Kerosene]] and [[Isopropyl alcohol|rubbing alcohol]] often give good results when working on [[Aluminium|aluminum]].
* [[WD-40]] and [[3-In-One Oil]] work well on various metals. The latter has a citronella odor; if the odor offends, mineral oil and general-purpose lubricating oils work about the same.
* Way oil (the oil made for machine tool ways) works as a cutting oil. In fact, some screw machines are designed to use one oil as both the way oil and cutting oil. (Most machine tools treat way lube and coolant as separate things that inevitably mix during use, which leads to tramp oil skimmers being used to separate them back out.)
* [[Motor oil]]s have a slightly complicated relationship to machine tools. Straight-weight non-detergent motor oils are usable, and in fact SAE 10 and 20 oils used to be the recommended spindle and way oils (respectively) on manual machine tools decades ago, although nowadays dedicated way oil formulas prevail in commercial machining. While nearly all motor oils can act as adequate cutting fluids in terms of their cutting performance alone, modern multi-weight motor oils with detergents and other additives are best avoided. These additives can present a copper-corrosion concern to brass and bronze, which machine tools often have in their bearings and leadscrew nuts (especially older or manual machine tools).
* [[Dielectric]] fluid is used as a cutting fluid in [[electrical discharge machining|electrical discharge machines]] (EDMs). It is usually [[deionized water]] or a high-[[flash point|flash-point]] kerosene. Intense heat is generated by the cutting action of the electrode (or wire) and the fluid is used to stabilize the temperature of the workpiece, along with flushing any eroded particles from the immediate work area. The dielectric fluid is non-conductive.
* Liquid (water or petroleum oil) cooled water tables are used with the plasma arc cutting (PAC) process.
* [[Neatsfoot oil]] of the highest grade is used as a lubricant. It is used in metalworking industries as a cutting fluid for aluminum. For machining, tapping and drilling aluminum, it is superior to [[kerosene]] and various water-based cutting fluids.<ref>{{Cite web|url=https://www.britannica.com/topic/neats-foot-oil|title=Neat's-foot oil {{!}} lubricant|website=Encyclopedia Britannica|language=en|access-date=2019-01-26}}</ref>