In precision grinding, plentiful and effective coolant is mission-critical. As abrasive compounds in grinding wheels remove material, temperature rises quickly. Oil-based and water-miscible coolants each help to ensure a stable thermal system that delivers the precision you’ve come to expect—while keeping the environment safe.

As you might guess, oil-based and water-miscible coolants have differing strengths and weaknesses. To sort them out, and to learn which is best for different types of precision grinding, we turned to one of the best minds in the industry for this topic: Tom Cappadona of Blaser Swisslube. Tom spent plenty of time working for us at STUDER earlier in his career, and he now lends his expertise to one of the best grinding fluid manufacturers in the industry.

The vital importance of coolant when precision grinding

A universal rule in manufacturing: when you change the temperature, you change the size of the parts you’re making. If you’re chasing microns with precision grinding, the temperature must remain consistent. All of the chips generated while part-making need to get out of the way as well, and coolant is an effective way to flush them out.

Using good, clean coolant also brings big benefits, including extended wheel life, reliable accuracy, less machine maintenance and a machine that looks better for longer.

The rundown on water-miscible coolants

If you need your coolant to be streamlined and less expensive, water-miscible options are the play. “It does a great job taking heat away from the part,” said Cappadona. “You don’t need any extra equipment or peripherals like you do with oil-based.”

“That said, water-miscible coolants have higher maintenance required because they can foul due to bacterial growth, and systems can be infected with fungus if not managed properly. It requires more monitoring and control. And for materials like HSS or carbide, you’re probably better off using an oil-based coolant if you’re able.”

Some bonus pro tips from Tom:

• Additives can be added, and in some cases, the concentrate has a biological package already built in.
• At changeover time, Blaser uses a cleaner for 7 to 10 days to kill any biofilms that might be present. Grinding is still totally okay to do during this time.
• If bacteria form, it’s probably because the water-miscible coolant is sitting still or not circulating, which reveals itself in elevated pH levels.
• Blaser hosts Lunch & Learns to offer training on maintaining their water-miscible coolant.

The rundown on neat oil-based coolants

It may cost a bit more in equipment and peripherals, but oil-based coolants are trusted for their ability to bring high MRR as well as peace of mind. “Oil does a better job than water, thanks to its lubricity and additives package, at not generating heat,” Cappadona said. “With materials like carbide or HSS, oil-based reduces friction/heat to achieve higher MRR.”

It’s important to have a high quality base oil: either hydrocracked, gas-to-liquid or polyalphaolefin (PAO). The flashpoint is very important too. Flashpoint is the temperature at which vapors become flames. For reference, the Blasogrind GTM 10 (near oil for HSS and carbide) has a flashpoint of 374 degrees Fahrenheit. Comparable coolants have flashpoints between 275 and 320 degrees.

On the downside, using oil-based coolant will require fire suppression and a chiller to keep the temperature down. This is a vital point about neat oil coolants that is worth repeating: fire suppression is an absolute must.

What coolant do tool grinders prefer?

Cappadona has seen both used, but many tool grinders turn to neat oil-based coolants for their higher lubricity (performance), ease of use and reduced cobalt leaching.

The WALTER DIAMOND series of tool grinders are known as 2-in-1 machines for their carbide grinding and PCD eroding capability. This requires a special fluid type, which at Blaser is the Blasogrind GTE 5. It has minimal grinding additives to minimize oxidation while eroding. This coolant is also an ideal fit for STUDER wire dress cylindrical grinding machines.

What coolant do cylindrical grinders prefer?

If a shop is doing tool and die work, chances are the workpiece is made of tungsten carbide, which contains cobalt. Working with cobalt virtually demands oil-based coolants, but again, Cappadona has seen both used in cylindrical grinding applications. “If you’re just grinding and there’s nothing extraordinary about what you’re doing, water gets the job done without the added peripheral.”

Cappadona also noted an interesting fact: with Blaser’s water-miscible coolants, additional additives can kick in with the right conditions. “On the neat oil side of things, the lubricity is the base, then there’s the additives. Those additives kick in at certain temperatures to add another layer of protection.”

What coolant do surface and profile grinders prefer?

Most applications performed by surface and profile grinding machines use water-miscible coolant. “But when you get into superabrasives, you’re more likely to see oil-based,” Cappadona said.

The verdict: which is better? Oil-based or water-miscible coolants?

We put Tom on the spot, and he answered diplomatically: he genuinely sees the perks of using both oil-based and water-miscible coolants. “Most of the time, when I walk into a shop, they’re already using coolant. The answer to oil-based or water-miscible is usually customer-driven. So it’s typically a matter of determining which coolant is the best fit.”

“I’ll say this: the machine stays cleaner with oil, but the operator doesn’t. Back in my on-machine days, I preferred water-miscible for that reason. But now that I have this career under my belt, I absolutely see and appreciate the advantages of oil.”

There are also additional considerations that can influence the coolant type you choose. Neat oil generally keeps machines cleaner, but cleaning the part after grinding can be more challenging depending on the next steps in the process.

Ready for Next-Level Precision Grinding? Reach out to UNITED GRINDING North America.

It’s a great feeling to help customers reach new levels of accuracy and productivity—all while quickly realizing ROI on an equipment purchase. Talk to us and let us know about your current applications and future ambitions.