Cutting Fluid or coolant is liquid used to cool and lubricate the cutting edges of machine tools and the pieces they are shaping. It is pumped over the cutting site of machines such as lathes, milling machines, shapers and saws.

Cutting fluid is most commonly an emulsion of oil and water however there are now synthetic cutting fluids available.

The properties that are sought after in a good cutting fluid are the ability to:

• keep the workpiece at a stable temperature (critical when working to close tolerances).
• maximize the life of the cutting tip by lubricating the working edge and reducing tip welding.
• prevent the growth of bacteria or fungi.

Cutting fluid may also take the form of a paste when used for some applications, in particular hand operations such as drilling and tapping.

Disposal of these used fluids will be regulated by the local Environmental Protection Agency. This is not only because of contamination with sump oils but also due to the soluble nature of the original compounds.

Other lubricants

• Kerosine has been used when working on aluminium.
• Lard for press tool work
• mineral oil