PM checklist
CNC machining centre: a preventive maintenance checklist
A CNC machining centre loses accuracy and time to dirty coolant, low way lube, a choked chip conveyor and a spindle that was allowed to run hot. This checklist is a starting point for those jobs. Intervals come from the machine manual and from your own alarms and scrap, not from a generic table. The method is in the preventive maintenance guide.
Key takeaways
- Daily CNC care is cleaning, lube level and coolant. Skip it and the expensive jobs arrive early.
- Record spindle temperature or vibration against a baseline. A single "OK" cannot show a drift.
- Chip conveyor and coolant tank are maintenance, not housekeeping. They cause alarms and rust.
- Separate operator checks from jobs that need the machine isolated and a skilled fitter.
- Shorten an interval when the same alarm repeats between PMs. Stretch it when the PM keeps finding nothing.
Each shift and each week
Operators can own the looking and the cleaning. Write the limit on the checklist so a new operator knows what "low" means.
| When | Check | What to record | Act when |
|---|---|---|---|
| Each shift | Way lube and hydraulic oil levels | Level against the sight marks | At or below the low mark |
| Each shift | Coolant level and how it smells or looks | Level, and a note if it is rancid or rusty | Low level, tramp oil, or a smell that means bacteria |
| Each shift | Chip conveyor running, and chips not packed in the enclosure | Cleared, or a jam found | Conveyor stalled, or chips against way covers |
| Each shift | Air supply pressure to the machine | The gauge reading | Below the pressure the manual specifies |
| Weekly | Clean the coolant tank screens and check concentration | Concentration if you use a refractometer | Outside the band your coolant supplier set |
| Weekly | Wipe way covers and check wipers for cuts or embedded chips | OK, or wiper damaged | A torn wiper, which lets chips onto the ways |
| Weekly | Listen for a new spindle or axis noise at idle | A note if the sound changed | A new tone, or a vibration you can feel on the head |
Monthly and on hours
These need a planned stop. Do not squeeze them into a changeover unless production has agreed the slot.
| Job | Usual trigger | What "done" looks like |
|---|---|---|
| Record spindle temperature and a vibration or noise baseline | Monthly, at the same speed | The number next to last month's number |
| Check tool-changer arm, pots and a sample of pull-studs | Monthly, or after a tool-change alarm | What was found, and any part replaced |
| Inspect way covers, cables and coolant hoses for rubs | Monthly | Photo of any rub, and whether it was dressed or replaced |
| Clean electrical cabinet filters | Monthly, more often in a cast-iron shop | Cleaned or replaced, and the date |
| Check backlash or a positioning test if your quality plan asks | Quarterly, or after a crash | The result, the program used, and who ran it |
| Change hydraulic and way-lube filters | OEM hours or calendar, whichever comes first | Hours, part numbers, and oil condition |
After a crash, do not "just reset the alarm". Inspect the drawbar, the tool and the axes before you hand the machine back. That inspection is a job of its own, with photos.
A worked example from a typical plant
Worked example (illustrative)
An auto-components shop near Pune has four CNC turning centres on two shifts. Coolant is topped up from a drum, and nobody writes the concentration. Over three months one machine throws repeated turret alarms, and another starts leaving rust on parts after a weekend.
The team adds a shift checklist: lube level, coolant level and smell, conveyor, air pressure. Once a week a technician records concentration and cleans the tank screen. Once a month they record spindle temperature at a fixed rpm and photograph the way wipers. Figures and the failure story are illustrative.
The rust pointed at concentration, which a weekly number would have shown. The turret alarms pointed at chips and a pull-stud check, which the monthly job covers. The checklist does not diagnose the spindle. It makes the drift visible.
Common mistakes
- Calling chip cleaning "the operator's problem" and then wondering why way covers fail.
- Recording spindle condition as OK. You need a number at the same speed each month.
- Letting coolant run until it smells. By then you already have rust and skin complaints.
- Doing the monthly job only when the machine is already down for a breakdown. That teaches the team that PM is optional.
- Using one checklist for a lathe and a machining centre. The tool changer and the axes are not the same.
How to put this list to work
Start with the machines that scrap parts or stop the cell. Give operators the shift checks and a technician the monthly readings. After a month, look at which lines were left blank. A blank line is either the wrong check or a check nobody believes in. Fix that before you add more tasks.
Sources
- Operations & Maintenance Best Practices Guide, Release 3.0 (opens in a new tab), U.S. Department of Energy, Federal Energy Management Program
- Maintenance of work equipment (opens in a new tab), Health and Safety Executive (HSE), UK
Frequently asked questions
What should be on a daily CNC checklist?
Way lube and hydraulic level, coolant level and condition, chip conveyor, air pressure, and a look for a new noise. Keep it short enough that a shift will actually do it.
How often should spindle vibration be checked?
Monthly is a sound start if you always measure at the same speed and write the number down. Check sooner after a crash, a new noise, or a run of poor finish.
Who should do CNC preventive maintenance?
Operators can clean, check levels and record the simple readings. Filter changes, axis checks and anything inside a guard belong to a trained technician, with the machine isolated.
Does this apply to a CNC lathe and a machining centre?
The daily care is similar. The tool changer, the axes and the spindle test are not. Split the checklist by machine type and follow that machine's manual.