Choosing the Right Cutting Oil

Cutting oil is critical to efficient metalworking. Whether drilling, grinding, reaming, or broaching, you run the risk of unwanted wear, oxidation and damage to your tool(s) and workpiece without it. 

The right cutting oil lubricates, keeps the cutting tool at an optimal temperature, and assists in chip removal. It enhances tool life, improves cutting quality, and safeguards the workpiece from potential damage. All of this makes it indispensable. See which oil type is best for your operation. 

Oil Type

Your options for cutting oil will fall into two main categories: straight and soluble. One is not inherently better than the other, they’re just different and each is more applicable for certain uses. 

Straight oils, made from mineral or petroleum oil, are undiluted and work best as lubricants for slower, heavy-duty applications. Straight oils have a better extreme pressure additive that prevents welding between the tool and the material being machined. Straight oils are also good at preventing any rust.

Soluble oils, like synthetic and semi-synthetic, are diluted. These lubricants contain emulsifiers, a mineral base, and other additives to provide good lubrication and heat transfer. There may be a rust-preventive constituent added as well for corrosion protection. Soluble oils work well as coolants. 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 definitely consider the hardness and machinability of your materials. For hard, low-machinability materials, such as stainless steel, you want a straight oil. With softer, ductile materials, like aluminum, go with soluble oils. 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 TrueGard specialty oils and lubricants here.