The Machine That Ate Its Own Bearings
A customer ran an indexer 24/7. The production manager told me “we fix it when it breaks.” Six months in, the indexer’s bearings failed catastrophically — the gearbox locked up, a shift was lost, and the repair cost three times what a planned overhaul would have. The root cause was not bad luck. It was no preventive maintenance. Nobody had relubricated the bearings, nobody checked the belt tension, nobody cleaned the air filter. The machine told us it was wearing down (temperature, noise, vibration) for weeks before it died. We just did not listen.
Preventive maintenance is not a bureaucratic chore. It is the cheapest insurance you will ever buy. This article lays out a practical schedule that actually works on the shop floor.
The Two Failure Modes You Are Fighting
Mechanical failure follows two patterns. The first is wear-out — predictable, time-based (belts stretch, filters clog, grease dries). The second is random — a bearing fails at 8000 hours or at 40,000 hours, you cannot know exactly, but statistics narrow the range. Preventive maintenance attacks wear-out on a schedule, and uses condition monitoring to catch random failures early.
Daily / Shift Checks (5 Minutes)
These are the checks the operator does at start-up. They take minutes and catch the obvious:
- Pressure gauge: Is the air pressure at setpoint?
- Leak check: Any hissing (air) or dripping (oil)?
- Abnormal noise: Does the machine sound right? A new whine is a warning.
- E-stop test: Press it once per shift. Does it stop the machine?
- Guard condition: Are all guards closed and undamaged?
If any of these fails, the machine is not run — it is tagged out. The cost of a 5-minute start-up check is trivial; the cost of running a machine with a failed e-stop is a lawsuit.
Weekly Checks (30 Minutes)
- Air filter bowl: Drain the water (auto-drain or manual).
- Lubricator: Is there oil in the sight glass? Top up.
- Chain/belt tension: Deflection at mid-span should be 1–2% of span.
- Cable dress: Any cable out of the track? Any pinched wire?
- Fastener check: Shake the handrail, the guard. Any loose bolt?
Monthly / Quarterly Checks (Half a Day)
- Linear guide relubrication: Pump grease until fresh grease emerges at the seals.
- Ballscrew preload: Check axial play (should be zero or within spec).
- Motor insulation: Megger the motor windings (if >100 kW, quarterly).
- Cooling fan: Clean the panel filter; check the fan runs.
- Safety relay: Bypass test — does the relay drop out when the guard opens?
Annual / Major Overhaul (1–3 Days)
- Bearing replacement (per manufacturer hours, not calendar).
- Gearbox oil change.
- Timing belt replacement (even if it looks fine — rubber fatigues).
- Encoder calibration check (against a reference).
- Full electrical inspection (torque the busbar, check terminations).
The principle: Do not maintain by the calendar. Maintain by the hour. A machine that runs three shifts wears three times faster than one that runs one shift. Convert every interval to operating hours and track it on the PLC or a simple counter. The indexer that ate its bearings had run 12,000 hours on original grease — a quarterly relube would have prevented it.
Make the Schedule Stupid-Proof
A maintenance schedule that lives on a spreadsheet fails. Operators forget. Make it visible and mandatory:
- Put the next-due tasks on a label on the machine itself.
- Use the PLC to lock the machine out when hours are exceeded (with a supervisor override).
- Keep a maintenance log on the machine (a clipboard or a screen) — sign every task off.
- Review last month’s failures in a weekly 15-minute meeting.
Where to Spend the Money First
If you cannot maintain everything, rank the assets by their downtime cost. A machine that stops the whole line (a bottleneck) gets monthly attention. A machine that has a backup gets quarterly. A light-duty auxiliary gets annual. ABC classification: A (critical, monthly), B (important, quarterly), C (spare, annual).
A One-Page Starter Schedule
| Interval | Task | Who |
|---|---|---|
| Every shift | Pressure, leak, noise, e-stop | Operator |
| Weekly | Drain filter, lube oil, belt tension | Operator |
| Monthly | Relube guides, check terminations | Technician |
| Quarterly | Bearing check, motor insulation, fan filter | Technician |
| Annual | Belt replacement, oil change, calibration | Outside/contractor |
The Bottom Line
Preventive maintenance is boring, repetitive, and invisible — until you skip it. The indexer that locked up was a failure of imagination, not engineering. Build the schedule, track it by operating hours, and make it mandatory. The best maintenance program is the one that runs the machine for 10 years with no surprise failures.
