Machining Guide: Cutting Fluid Tips for Holemaking Operations

For starters, many shops upgrade their machine tools and other machining technology without considering whether they’re using the best possible cutting fluids. Filling the sump with the sulfur-based oils or water-soluble fluids of yesteryear are a little like putting unleaded fuel into a high-performance sportscar—it might run for a while, but you'll eventually run into performance problems. 

Cutting fluids experts will tell you that replacing these outdated cutting fluids with modern, premium grades of semi-synthetics helps to reduce costs and improve productivity. This is mainly due to these fluids’ high-lubricity esters, which eliminate the need for chlorinated paraffin or sulfur-based EP compounds.

These esters create a tight boundary layer around oil droplets, keeping them intact during metalworking operations. It also enhances their lubricity and thus reduces wear on cutters and machinery. And because they're less likely to break down under pressure at today’s higher cutting speeds and feedrates. Finally, and just as important is their greater friendliness to workers and the environment alike.

Today’s cutting fluids offer other advantages as well. Since they’re more efficient at lubrication, less concentrate is needed when mixing up a fresh batch of coolant. This cuts operating costs while limiting the amount of “food" for bacteria lurking in any machine tool sump, resulting in a nicer-smelling shop and no “Monday morning stink.”

With that, they tend to reduce the amount of time spent on fluid maintenance and sump cleaning. And since these high-ester fluids increase the emulsion’s water content, they enhance its cooling ability, a benefit that’s critical during holemaking.

Cutting fluids serve two fundamental purposes across all machining operations: reducing heat and providing lubrication. In processes like drilling, milling, and threading, substantial heat is generated at the point of contact between the cutting tool and workpiece. Without coolant to absorb and remove this heat, both tool and workpiece can degrade. Equally important is lubrication—cutting fluids help reduce friction between the tool and material, improving surface finish, lowering cutting forces, and extending tool life. Understanding these two core functions is key to optimizing coolant usage and achieving consistent machining results.

HPC is just as its name describes—a high-pressure auxiliary pumping system that pushes coolant through the cutting tool at 300-psi or more (often way more). This action removes heat from the work zone while blasting away chips and swarf, usually breaking them up in the process. As one might expect, HPC significantly improves tool life and supports feeds and speeds much higher than is possible with the standard pumps found on most machine tools. 

As noted, a filtration unit will be needed to avoid damaging the pump. But because this also removes the microscopic bits of metal and dirt generated during any machining operation, tool life and part surface quality are further improved. Here again, be sure to check with the manufacturer for proper sizing advice. 

While water-based coolants are ideal for high-speed machining with carbide tools due to their superior heat dissipation, high-speed steel (HSS) tapping often benefits more from heavier oil-based coolants. Tapping is a demanding operation that requires excellent lubricity to prevent galling and reduce torque. Oil-based fluids offer the film strength needed to protect delicate threads and minimize tool wear. Choosing the right coolant based on tool material and operation type ensures better performance and longer tool life.