Metalworking fluids cover the cutting and grinding fluids used in turning, milling, drilling, tapping and grinding, in both neat oil and water-miscible forms.

These fluids do four jobs at once: cool the cutting zone, lubricate the tool and workpiece interface, flush swarf clear of the cut, and protect the freshly machined surface from rust. Water-miscible products lead on cooling and suit higher-speed work, while neat cutting oils lead on lubrication and are used for heavy, slow operations such as broaching, gear cutting and deep-hole drilling where finish and tool life matter most.

Mix control keeps a water-miscible fluid working. Check concentration with a refractometer, always add concentrate to water rather than the reverse, skim tramp oil off the sump, and act on any sour smell, which signals bacterial growth.