Your options for cutting oil will fall into several categories: straight, soluble, semi-synthetic, and synthetic.
Straight oils, made from mineral or petroleum oil, are undiluted and work best as lubricants for slower, heavy-duty applications. Unlike the excellent heat transfer capabilities of synthetic (made from organic esters and other compounds) and semi-synthetic oils, straight oils do not work well as coolants.
Soluble oils, like synthetic and semi-synthetic, are diluted. These lubricants contain emulsifiers, a mineral base, and other additives to provide good lubrication, heat transfer, and corrosion protection. These oils are the most common and cost-friendly.
Some lubricants are more compatible with certain materials than others. When deciding on a cutting oil, you should differentiate between hard, low-machinability materials, such as stainless steel, and softer, ductile materials, like aluminum. Tougher metals require tougher cutting oils with greater lubrication and anti-weld capabilities to prevent build up on the tool.
It may also be helpful to choose a non-staining oil for aluminum and brass parts. Cutting oils that contain active sulfur can stain aluminum and brass. Active sulfur and chlorine are often found in cutting oils with a heavy concentration of extreme pressure (EP) additives.
Ultimately, the cutting oil that you choose will depend on the nature of the operation. Are you grinding? Are you thread-cutting? Cutting oils serve specific functions based on the difficulty and speed of the machining.
Grinding, drilling, and milling are often done at higher speeds with low-viscosity oils. The cutting oil’s main function will be cooling, especially with a synthetic cutting fluid, since the thinner, diluted fluid carries heat away more efficiently. Thread-cutting and broaching, however, require more work and slower operating speeds. A highly viscous oil is needed to reduce friction and lubricate the surface.
You can best choose your cutting oil by distinguishing between situations that emphasize a need for cooling and situations that emphasize a need for lubrication. A strong evaluation of the metal’s properties, as well as the machining method, can indicate which cutting oil will prevent corrosion or heat-related damage.
View our full list of Houghton specialty oils and lubricants here.