Metal Cutting fluids are an instrumental part of metal machining due to their improvement of the tool life, reduction of the work piece thermal radiation, flushing away chips from the cutting area, and improving the surface finish.
There are four main categories of metalcutting fluids and cutting oils:
Straight metal cutting oils
These oils are non-emulsifiable and very useful in metal machining operations where they function in undiluted form. Their composition is a base mineral or even petroleum oil. Often they contain polar lubricants like vegetable oils, fats and esters. They may also contain extreme pressure additives including sulphur, chlorine, and phosphorus. To achieve the best lubrication you can use straight metal cutting oils, however they may have poor cooling characteristics.