Perform Preventive Maintenance on the Fly and Minimize Downtime

The easiest way to avoid missed delivery dates and costly CNC machine repairs is to perform Preventive Maintenance (PM) on a regular basis. “Up to 40% of the repair work that I see could have been prevented by PM,” said Darryl Hardt, Assistant Manager of Service Training for Doosan Machine Tools America. “But tight production schedules can make it difficult to find time to follow the PM service schedules as outlined in the manual.”

This is why Doosan has developed a system that provides many of the benefits of Preventive Maintenance while fitting into the reality of operations in the real world. We call it the 6 F Program for Fluids, Filters, Fans, Function, Foundation and Fatigue.

The 6 F Program

“The 6 F program is mostly based on daily observation, common sense and reacting to small situations before they become major incidents where you have to tear the machine down to fix it,” Darryl said. There are 6 F programs for horizontal turning centers and vertical machining centers, but we’ll outline the general principles here.


Fluid levels, fluid cleanliness and fluid age play a dynamic role in the reliability of the machine’s operation. Fluids include, but are not limited to: hydraulic oil, lube oil, gear oil, chiller oil, air oil, grease and similar items.

Darryl’s tip: “If something smells burnt or musty when you walk up to the machine, some of the fluids may need changing.”


Filters not only need to be cleaned, they need to be unobstructed and intact. A torn or damaged filter will allow pollutants into the air or oil, and blocked filters will limit flow, resulting in malfunction.

Darryl’s tip: “Filters that are clogged with dirt can suffocate the component. Also use the right filter. Improvised filters may have holes that are too large, allowing contaminants to enter the inner working.”


Fans not only need to be operating, they need to be cleaned. They also need to be unobstructed and intact. A malfunctioning, blocked or dirty fan will limit airflow to areas that require it for cooling.

Darryl’s tip: “Keeping components at the proper temperature enhances their efficiency and reduces wear. A broken $20 fan can contribute to the premature failure of a costly servo motor.”


Most items are on a machine because they are needed. Never remove items, especially those related to safety.

Darryl’s tip: “There are buttons all over the machine that provide functions that help operate the machine. If you press a button and it doesn’t work, it should be checked. If it mis-operates once, it’s an abnormality...twice, it’s a curiosity...three times, it’s a problem.”


All machines will “settle” in their foundation. Over time, levelness of the machine can change. Crashing and vibration can cause a machine to “walk” if not lagged to the floor.

Darryl’s tip: “The entire geometry of the cutting area is based on the machine being level, square and parallel. Small variations in the foundation manifest as large deviations in cutting accuracy. Consider checking and re-leveling your machine after a few weeks and again every time you perform PM.”


A worn-out machine does not run well. Small issues, like a worn or damaged wiper on a way cover, can lead to large expensive ball screw and LM guide repairs if left unaddressed. Timing belts and drive belts that are worn, but “left alone until dead,” turn a simple repair into a time-consuming and costly one.

Darryl’s tip: “When an O-ring deteriorates, you may notice a leak of hydraulic fluid. Replacing those O-rings is a no-brainer. But when you take it a step further and think about the piston seals inside the machine, you may notice that replacing them brings the cylinder back to catalog spec pressure, helping functionality.”

Unloved, but Essential

Few machinists enjoy Preventive Maintenance, but ignoring it can result in your machine (aka your money maker) quite literally falling apart. Taking shortcuts on repairs and paying attention only to things on the surface and not thinking about what’s going on in the inside of a component leads to failure and a domino effect on other functions of a machine.

“Does using the 6 F Program take the place of following the Preventive Maintenance schedules as outlined in the manual that came with your machine? Of course not,” Darryl said. “But it will provide you with a fighting chance to keep your machine in operation and a daily PM awareness that may even cause you to pull out that manual and look at it once in a while.”

Need Service Help?

Would you like to know more about the 6 F programs or have a service question about a Doosan machine? Drop a line at love to talk maintenance.

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