Recognizing Machine Trouble During a Run
Spot drift, noise, vibration, leaks, and fluid changes during a run, and know when to stop and who to call.
Table of contents
Machines nearly always warn you before they fail. A dimension creeps, a sound changes, a smell shows up, or oil turns a strange color. You stand beside the machine all shift, so you are the first person who can catch it. Calling it early can mean a five-minute fix. Missing it can mean a bin of scrap, a wrecked spindle, or an injury. Your job is to notice, stop when you should, and report clearly. Diagnosing and repairing is up to maintenance.
What You Will Be Able to Do
- Learn what normal is for your machine, so changes stand out.
- Read a pattern of measurements and tell tool wear from other causes.
- Recognize warning sounds, heat, smells, and fluid changes.
- Decide when to stop the machine and when to keep running and report.
- Give a report that maintenance can act on.
Know What Normal Looks Like
You cannot spot a change if you do not know the starting point. In your first hours on a machine, learn these:
- How it sounds at idle and in the cycle
- The usual readings on pressure and temperature gauges
- The normal cycle time
- The normal color and level of its fluids
- How the parts look and feel coming off
Ask an experienced operator what normal is for that machine. Each one has its own habits. Then, on each shift, walk around it once while it runs, and use your eyes, ears, and nose.
When Parts Drift
Drift means measurements slowly moving in one direction. The most likely cause of parts gradually moving out of tolerance over an hour or more is tool wear. As a cutting edge loses its sharpness, it wears back and pushes away from the work a little more. Diameters you turn on the outside get larger, and bores get smaller.
Here is how that looks on paper. A shaft has a spec of 0.750 inch, plus or minus 0.003, so the limits are 0.747 and 0.753.
| Check | Reading (inches) | Change |
|---|---|---|
| 8:00 | 0.7502 | Start |
| 9:00 | 0.7509 | +0.0007 |
| 10:00 | 0.7515 | +0.0006 |
| 11:00 | 0.7521 | +0.0006 |
| 12:00 | 0.7528 | +0.0007 |
Every part is good, but the size is growing about 0.0006 inch an hour. At that rate the 1:00 check would read about 0.7534, which is over the limit. Call your setup tech now, while the parts are still good. A tool change or an offset is their decision unless you are trained and authorized to do it.
The pattern often tells you more than one number does.
| Pattern | Likely cause | What to do |
|---|---|---|
| Slow, steady move in one direction | Tool wear | Call it before it reaches a limit |
| Sudden jump | Chipped tool, shifted fixture, new batch of stock | Stop and report it |
| Moves in the first hour, then settles | Machine warming up | Note it, and follow the warm-up procedure |
| Random scatter | Loose workholding, worn bearings, uneven stock | Stop and report it |
| Burrs growing or finish getting worse | Dull tool | Tell the setup tech |
Vibration and New Noises
If you hear a new grinding noise or feel a new vibration, stop the machine safely and report it to your supervisor or maintenance. Do not run it to the end of the shift to see if it clears up. Bearings and gears do not fix themselves, and running them can turn a small repair into a major one.
| What you hear or feel | What it may mean |
|---|---|
| Grinding | Worn bearing or gears, metal on metal |
| High squeal | Slipping belt or a dry bearing |
| Knock or bang | Loose part, worn coupling, broken tooth |
| Hiss | Air or hydraulic leak |
| Pump whine or rattle | Pump short of oil, or pulling in air |
| Chatter during a cut | Dull tool, loose workholding, wrong settings |
| Shaking you can feel on the guard or floor | Loose mount, out-of-balance part, failing bearing |
Keep your hands off moving parts while you check. Do not remove a guard to get a better look. Guards stay on, and maintenance removes them under lockout.
Heat and Smells
A part that runs hotter than usual is often working too hard. A hot bearing housing, motor, or hydraulic tank can show that a failure is on its way.
| What you notice | Possible cause | What to do |
|---|---|---|
| Electrical burning smell or smoke | Overheated motor or wiring | Shut down, tell your lead, and be ready to follow the fire plan |
| Burnt oil smell | Overheated oil, slipping clutch or belt | Stop and report it |
| Bearing or motor too hot to go near | Failing bearing, overload | Stop and report it |
| Hydraulic temperature gauge above its usual range | Cooler problem, low oil, or an overworked pump | Report it, and stop if it reaches the limit |
| Rotten-egg smell from coolant | Bacteria growing in the sump | Report it |
Do not touch a surface to see how hot it is. Do not open an electrical panel. That work belongs to a qualified person.
Fluids and Leaks
Healthy hydraulic oil is usually clear and amber. Any change in color is a message.
Milky white oil usually means water has gotten into it. Water ruins the oil's ability to lubricate, rusts parts from the inside, and can quickly damage pumps and valves. Shut down the machine and notify maintenance. They can have it tested.
Air can also turn oil cloudy. Foamy oil with air in it tends to clear from the top as bubbles rise, while oil with water stays milky. You do not have to sort out which it is. Report it either way.
| What you see | Likely meaning | What to do |
|---|---|---|
| Milky white hydraulic oil | Water contamination | Shut down and notify maintenance |
| Foamy or bubbly oil | Air getting into the system | Report it now |
| Dark oil with a burnt smell | Oil overheated | Report it |
| Fresh oil under the machine, or the level dropping | Leak | Report it, and clean it up so no one slips |
| Water in an air filter bowl | Wet compressed air | Report it |
| Coolant low, dirty, or foamy | Sump needs attention | Report it |
Do not top up a reservoir with whatever is nearby. The wrong fluid can damage the system, and topping up can hide a leak.
Warning: Never feel for a hydraulic leak with your hand. A pinhole leak under pressure can shoot oil through your skin. Stay clear, and shut the machine down. Treat any injection as a medical emergency, even if it looks small.
Other Warning Signs
- Cycle time getting longer. A machine that takes longer to do the same work is often fighting something.
- The same alarm again and again. An alarm you keep clearing is a problem you are hiding.
- Gauges moving out of their usual range. Low air pressure or sagging hydraulic pressure can show up in the parts next.
- More jams than usual. Worn tooling or bad stock often shows up here first.
When to Stop
You will not be blamed for stopping a machine that needed it. If in doubt, stop and ask.
| Stop now | Keep running and report |
|---|---|
| Smoke, burning smell, or fire | Slow drift still well inside limits |
| New grinding, banging, or heavy vibration | Small change in cycle time |
| Milky hydraulic oil or a spraying leak | Slight drip with the level holding |
| Guard, interlock, or E-stop problem | Coolant odor |
| Parts out of tolerance | Low-level warning on a consumable |
To stop safely, use the normal stop at the end of a cycle if that does not add danger. Use the E-stop if someone could get hurt or the machine could crash. Then keep hands out, and keep other people away. Do not start taking things apart. If anyone has to reach into the machine, it must be locked out first.
How to Report It
A good report saves maintenance a lot of time. Give them these facts:
- Which machine, and what you noticed.
- When it started and how often it happens.
- What changed just before, such as a new tool, a new batch of stock, or a changeover.
- What you did.
- Which parts may be affected.
"The press sounds weird" does not give anyone much to go on. Compare it with this: "Press 7, grinding noise from the flywheel end since about 2:15, with vibration I can feel on the guard. It started right after changeover. I stopped it at the top of the stroke. The last good check was 2:00, and I tagged bin 14."
Then finish the job:
- Hold and tag any suspect parts.
- Fill out a repair ticket if your plant uses them.
- Write it in the log and your pass-down notes.
Common Mistakes
| Mistake | What it costs |
|---|---|
| Waiting until the end of the shift to report | A small repair becomes a major one |
| Waiting for parts to go out of spec | Scrap that a trend would have prevented |
| Resetting the same alarm over and over | A real failure with no warning |
| Removing a guard to look inside | An injury, on top of the problem you had |
| Feeling for a leak or heat by hand | Oil injection injury or a burn |
| Reporting "it sounds funny" | Maintenance has to start from nothing |
Check Your Understanding
1. A bore has been getting a little smaller at each hourly check for three hours. Parts are still in spec. What is the likely cause, and what do you do?
Tool wear is the likely cause, since a worn tool cuts smaller bores. Tell your setup tech now, before the size reaches the limit.
2. Parts have been steady all morning, and then one check jumps 0.004 inch. What is different about this?
A sudden jump does not look like wear. Think of a chipped tool, a shifted fixture, or a new batch of stock. Stop and report it, and hold parts back to the last good check.
3. You check the sight glass on a hydraulic press, and the oil looks like coffee with cream. Your lead is away. What do you do?
Shut down the machine and notify maintenance. That color usually means water in the oil, and running it can damage the pump and valves.
4. A fine mist is coming from a hose fitting on a press. A coworker offers to find the exact spot by running a finger along it. What do you say?
Stop them. High-pressure oil can go through the skin. Shut the machine down and call maintenance.
Key Takeaways
- Learn what normal is for your machine, so you can see changes early.
- Slow, one-way drift usually means tool wear. Call it before parts go out.
- New grinding or vibration means stop safely and report it.
- Milky hydraulic oil usually means water. Shut down and notify maintenance.
- Never use your hand to find a hydraulic leak or a hot spot.
- Report what, when, what changed, what you did, and which parts are affected.