Clear Versus Dark Cutting Oil: Know the Difference

The choice between clear or dark cutting oil depends on your threading machine's rpm rating (revolutions per minute). Simply put, dark-cutting oil is for high-speed (machine) threading; clear-cutting oil is for low-speed (hand) threading.

Before diving into the important differences between clear and dark cutting oils, we must understand what cutting oil is and its uses. 

What is Cutting Oil? 

It’s a type of coolant and lubricant designed specifically for metalworking processes, such as thread cutting, sawing, turning, tapping, broaching, and drilling all types of metals.

Cutting oils contain activated sulfur to provide anti-weld properties, reduce friction and prevent excessive heat generation, thus minimizing material expansion that leads to ill-fitting joints. 

Cutting oils will: 

●    Ensure quick, accurate, and high-quality cuts
●    Maximize the life of your cutting and drilling equipment
●    Extend the life of your tools and increase their performance
●    Improve machine finish, and lubricate to reduce tip welding 
●    Prevent pitting and metal seizures

Let's take a closer look at clear and dark-cutting oils; specifically, what they’re made of and their specific uses. 

Clear Cutting Oil

Clear Cutting Oil is a blend of high-quality mineral oils with a sulfur base. It is used for cutting clean, unbroken threads during manual or low-rpm threading machine operations on small steel and brass pipe sizes. It can also be used for hacksawing and light drilling.

Hercules® Clear Cutting Oil is compounded for cutting clean, unbroken threads using manual or low-torque threading machine operations on small steel or brass pipe sizes. 

Low torque means less work and, therefore, less heat generated as well as a longer life for tools. This product is an excellent lubricant for cutting sharp threads and contains activated sulfur and extreme pressure-antiwear additives. Hercules® Clear Cutting Oil offers better heat dissipation and has a long-lasting formula with less residue backup. It will also not stain copper or brass materials. 

Another option is Harvey™ Clear Cutting Oil, formulated to give sharp, clean threads and extend die life. It can be used on most metals and contains activated sulfur and extreme pressure- antiwear additives. 

You can purchase Hercules® Clear Cutting Oil and Harvey™ Clear Cutting Oil at your local hardware store or supply house. 

Dark Cutting Oil

Dark Cutting Oil is comprised of an extra heavy blend of high-quality mineral oils with a sulfur-lard base to keep tooling and work cool when used on high-speed threading machines. Dark Cutting Oil will enable you to cut clean, sharp threads on steel or brass pipe. It is ideal for thread cutting, tapping, broaching, drilling, or any application where high speeds and quality finishes are required.  

Hercules® Dark Cutting Oil significantly extends tool life and reduces labor time. Its special mixture of sulfonated and chlorinated oils provides high film strength, keeping machines running cooler and extending the life of your dies. 

Formulated for high-speed threading machines, Hercules® Dark Cutting Oil has no offensive odors. Its anti-mist and is not affected by the weather. Another option, Oatey® Dark Thread Cutting Oil, is also designed for use with high-rpm machine operations for threading steel and brass pipe. Once again, you can purchase Hercules® Dark Cutting Oil and Oatey® Dark Thread Cutting Oil at your local hardware store or supply house. 

Tips when using cutting oils

●    Wear safety glasses with side shields to protect eyes from metal shavings. 
●    Be sure to start the flow of oil before tooling is in contact with the work. 
●    Oil flow should hit the point of friction for best results.
●    Always use properly ground chasers and dies with cooling lubricant to obtain sharp, clean threads without burrs.

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