Keller-Heartt Blog: Choosing the Right Cutting Oil
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Choosing the Right Cutting Oil

Without using the appropriate cutting oil for the type of metal and metalworking you wish to do, drilling, grinding, broaching, and other methods of metal machining can result in unwanted wear, oxidation, and chip weld. Costly wear is avoidable if certain criteria are considered, such as operating speed or lubricant formula. Since the right cutting oil can make all the difference, let’s learn about the different types of cutting oil and their best uses.

Oil Type


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.

Metal Type


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.

Operation Type


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.