The Vibration Signature Reference

Why this matters

Anything that spins, pumps, or moves air tells you what is wrong with it through how it shakes and sounds, long before it fails outright. A tech who can read a vibration signature catches a worn bearing or a loose mount on the first visit instead of after the part lets go and takes others with it. You do not need lab instruments. You need to know what each kind of fault feels and sounds like, and where to put your hand.

What vibration actually is

Vibration is force you can feel because something is not perfectly balanced, aligned, or tight. A small amount is normal on any running machine. The diagnostic value is in the change: a machine that ran smooth and now buzzes, or shakes at a frequency it never did before, is telling you a specific part is failing. Always compare to "how it should feel," which means knowing the baseline or comparing to a matching unit that runs right.

Read it by frequency and feel

Vibration sorts into a few families by how fast it repeats relative to the rotating speed. You can feel the difference with your hand and hear it in the pitch.

Imbalance is the most common and the easiest to confirm: it is steady, it scales gently with speed, and it often comes from buildup you can see and clean off.

Where to put your hand

Touch the housing near each bearing, near each mount, and on the frame. You are mapping where the vibration is strongest, because that points at the source.

• Strongest at one bearing end points at that bearing or what it carries.
• Strongest where two parts couple points at misalignment or a worn coupling.
• Strongest at the mounts or it moves when you push points at looseness, not an internal fault.
• Felt everywhere equally often means the whole assembly is loose from its base or the base itself is moving.

Back of the hand reads high-frequency buzz better; flat palm reads heavy low shake better. Use both.

Bearings: catch them early

A failing bearing is the most common signature that escalates from annoying to catastrophic. It starts as a faint high whine or growl, often only at certain speeds. It progresses to a rumble you feel through the housing, then to a grind, then to seizure. The moment you hear a clean machine develop a growl at a bearing, you have time to plan a replacement. Once it grinds, you are on borrowed time and a seizure can damage the shaft, the housing, and whatever it drives.

Looseness fakes other faults

Loose hardware and worn mounts produce rattly, changeable vibration that mimics balance or bearing problems. The tell is that it is inconsistent and it responds to pressure: push on the assembly and the noise changes, the shake moves, or it briefly quiets. Always rule out looseness first because tightening costs minutes and replacing the wrong part costs a callback. Check mounts, fasteners, guards, and panels before you condemn anything internal.

Resonance: the fault that is not a fault

Sometimes a machine shakes hard only at one speed and smooths out above and below it. That is resonance, where the running speed matches the natural frequency of the structure. The part is often fine; the mounting or surrounding structure is amplifying normal vibration. The fix is to stiffen the mount, add mass, isolate it, or avoid the speed, not to replace the running component. Misreading resonance as a bad part is a classic way to throw money at a machine that needed a better bracket.

References

• OSHA guidance on machine guarding and rotating-equipment hazards
• Trade-standard practice for vibration analysis and rotating-equipment condition monitoring
• Bearing and component manufacturer documentation for failure-progression indicators
• See related: reading a failed part for the real cause; tighten and test before parts