Misalignment rarely announces itself. A motor and gearbox can run for months looking perfectly normal while an offset coupling quietly overloads both sets of bearings on every single revolution. By the time vibration or heat gives it away, bearing life has often already been cut in half. A checklist run the same way on every alignment job is what keeps that from happening. Sign up to attach as-found and as-left alignment data to every asset and get flagged the moment a train drifts back out of tolerance.
Why It Matters
Alignment tolerance is not one fixed number, it tightens as RPM climbs, since the same offset creates proportionally higher cyclic load at higher speed. A cold alignment done without accounting for soft foot and thermal growth can measure perfect at rest and still fail once the machine reaches operating temperature.
The Six Fundamentals Every Alignment Job Depends On
Offset
Parallel gap between shaft centerlines, measured in mils or mm
Angularity
Shaft centerlines meeting at an angle, expressed as slope per span
Soft Foot
Frame distortion when a foot is bolted down, corrected before alignment starts
Thermal Growth
Cold offset deliberately set so the machine lands true once hot
RPM Tolerance
Acceptable offset tightens as running speed increases
As-Found Value
Recorded before correction, the real diagnostic on what moved and why
Before You Align: The Pre-Job Checklist
Mounting surfaces clean: feet and baseplate checked for rust, paint, or debris that would throw off shimming
Soft foot corrected first: each foot checked and shimmed before any centerline reading is trusted
Coupling and shafts rotated together: both shafts turned through the measurement arc, never one alone, to cancel out runout
Thermal growth targets loaded: cold offset values pulled from OEM data or prior hot checks before adjusting anything
RPM-based tolerance selected: correct speed and coupling span entered so the acceptable band is not just a guess
As-found and as-left recorded: both values logged against the asset, not left on a printout that never makes it back to the file
Stop Losing Alignment Records To A Printout
OxMaint attaches every as-found and as-left alignment reading to its asset, tracks drift over time, and flags a train the moment it moves back out of tolerance. Sign up for a free trial to run it on your own alignment checklist, or book a demo to see it configured for your plant.
Rotating Equipment, Alignment Focus & Typical Frequency
| Asset |
Alignment Focus |
Recheck Frequency |
| Motor-to-Gearbox Trains |
Tight offset and angularity tolerance, thermal growth compensation critical |
After every reinstall, annually on critical drives |
| Fans & Blowers |
Soft foot common on fabricated bases, coupling wear from belt tension |
After bearing or coupling replacement |
| Pumps |
Pipe strain plus thermal growth at process temperature |
Every planned outage, or on rising vibration trend |
| Mill Drive Couplings |
High torque loading amplifies even small residual offset |
Continuous drift check via vibration, physical recheck yearly |
The Takeaway
Good alignment is a sequence, not a single measurement, soft foot corrected first, both shafts rotated together, thermal growth targeted, and the RPM-appropriate tolerance held at the end. Skip a step and the printout can read perfect while the bearings still fail early.
Frequently Asked Questions
Q
Why does alignment tolerance change with RPM?
Centrifugal forces from an offset coupling grow with the square of speed, so the same misalignment that is harmless on a slow-turning fan can be destructive on a machine running at several thousand RPM. That's why tolerance charts are always graduated by speed, not a single fixed number for every machine.
Q
Why align to a cold offset instead of zero?
Motors, gearboxes, and pumps expand as they heat up during operation, and that growth shifts the shaft centerlines. Aligning to a perfect zero at ambient temperature usually means the machine drifts out of tolerance once it reaches operating temperature, so the cold target is deliberately offset to land true when hot.
Q
If alignment was done six months ago, why is it out again already?
A machine that goes out of tolerance again after being properly aligned usually points to something else moving it, a settling foundation, changing pipe strain, or a recurring soft foot. The as-found reading from the recheck is the real clue to what upstream problem needs fixing, not just a reason to realign again.
Turn Every Alignment Job Into A Tracked Asset History
OxMaint stores as-found and as-left alignment data per asset, tracks drift across rechecks, and fires a work order the moment a train moves out of its RPM-based tolerance. Sign up for a free trial to explore it on your own rotating equipment, or book a demo to see it configured for your plant.
