Don't Cut Costs Here: Spending More on Metalworking Fluids Boosts Machine Shop Profits

Reducing ‘Carry-Off’

That makes it easy to argue that a small performance increase more than offsets the cost of any metalworking fluid.

One major consideration for shops choosing cutting fluids should be their tendency to “carry off,” which has a significant impact on cost, he says.

“Carry-off is the amount of fluid that sticks to the chips and workpiece and is directly related to the size of the oil droplet and its wetting factor,” he says. The more fluid that’s carried off, the more workers must add to replenish it.

Treese offers two analogies. The first is that of a sump filled with pingpong balls vs. one filled with softballs. Smaller droplets, i.e., those that are like pingpong balls, carry away less fluid and are therefore less expensive.

Read More: How Synthetic-Based Cutting Fluids Can Boost CNC Cutting Speeds

Second is the wetting factor. Large droplets that cling to the chip surface are more prone to carry-off, increasing fluid loss, while ones with good wetting form “a nice, flat puddle” that resists carry-off, and again, are more cost-effective.

Perhaps most importantly—to the machinist, at least—is the performance of cutting fluids, sometimes referred to as cutting oils or machining oils.

“The space between the cutting tool and chip is minuscule, so smaller oil droplets and higher wetting allow more lubricant and water to squeeze into the cutting zone, increasing effectiveness,” Treese says. “Think of it from an engineering standpoint—if you have two plates of metal rubbing on one another, would you want several big ball bearings carrying that load, or several hundred smaller ones?”

Cutting Fluid Maintenance

Another reason to periodically reevaluate cutting fluid choices is, as Treese implies, higher machine performance. Spindle speeds on CNC machining centers are much higher than those of yesteryear, with 12,000 rpm or greater (often much greater) quite common.

And many CNC machine tools—lathes and machining centers alike—are now equipped with high-pressure coolant (HPC) systems. The “tiny droplets” just mentioned must therefore withstand pressures of 1200 psi and higher without creating excess amounts of foam.

Whatever the brand or type of cutting fluid, proper maintenance is key to long-term performance, the two experts agree. Suggestions include:

• Avoiding the use of hard water. Reverse osmosis or deionized waters are best.
• Acknowledging that sump skimmers are a must on any machine tool.
• Investing in a coolant recycling system for fast cleanouts.
• Routinely checking coolant concentrations with a refractometer and mixing makeup fluids accordingly.

The last item brings up a common oversight: Always add the concentrate to the water, not the other way around.

Better yet, buy a coolant proportioner for the most accurate mixing. “And don’t be afraid to ask for help from your fluid provider,” says Castrol’s Jennifer Johns. “There’s a reason why we and others carry so many different formulations, and deciding which one is right for your application isn’t always easy.”

Lastly, modern cutting fluids share another similarity with cutting tools—they often need a higher rpm to be effective.

During one recent customer visit, Master Fluid Solutions’ Treese delivered the welcome news that the business could and should increase spindle speeds, often by 30 percent or more. Doing so was necessary to generate the heat needed for good chip flow.

“Modern cutting fluids do such a good job of cooling that chips will stick to the carbide if the rpm is too low, resulting in built-up edge and flaking,” he says. “It’s not unlike touching your tongue to a frozen flagpole. That’s also why it’s crucial that shops maintain the correct concentration, which is key to coolant longevity and a reproducible cut. I can’t stress this enough.”