Special cases
Not every drive is two horizontal machines and a short coupling. These cases need a different method or different tolerances.
Belt and sheave alignment
Belt drives need sheave alignment, not shaft-to-shaft alignment. The goal is for the grooves to lie in the same plane, with the shafts parallel. Three errors matter:
| Error | What it is | Effect |
|---|---|---|
| Offset | Grooves are in different planes, shafts parallel | Belt sidewall wear, edge load, noise |
| Vertical angle (tilt) | Shafts not level with each other | Belt walks to one side and wears |
| Horizontal angle (toe) | Shafts not parallel when seen from above | Belt twists and runs hot |
- Use a laser tool or a straight edge on the sheave faces, with the belts off.
- A sheave that wobbles shows as a pulsing belt. Check face runout.
- Set tension by the maker deflection or frequency method only after the sheaves are aligned.
- Typical sheave alignment limits are about 0.5 degree angular and 1.5 mm per metre of centre distance. Use the belt maker value if you have it.
Vertical pumps and flange-mounted drives
For a flange-mounted motor the flange fits set the alignment and there is no foot move. Check the face runout and the spigot (rabbet) fit, and look for a gap on the flange face. Shim between flange faces only with the maker approval. Hold readings for the weight of the motor with a clean, dry mating face.
Machine trains
With three or more machines (motor, gearbox, pump), pick the machine that is heaviest, hardest to move or most sensitive as the fixed reference. Align the neighbour first, then the next. Then re-check the first pair after the second is done: moving the middle machine disturbs both couplings. Tools that handle trains compute all moves at once.
Cardan (universal joint) shafts
These need the end shafts parallel with a deliberate small angle at the joints so the needle bearings keep rolling. Offset shafts in a parallel arrangement are common, and the joint angles must be equal and opposite. Follow the maker angle range.
Machines that cannot be moved
If a machine is grouted, piped or too heavy, use the other as the movable machine and accept longer shim stacks, or shim both. Where nothing can move, the base needs rework. Do not accept a misalignment outside the maker limit because the job is hard.
Offset shafts and angled drives
Where the shafts are deliberately offset, as with some right-angle or parallel-shaft gearboxes, the coupling sees a combination. Follow the gearbox and coupling maker. The measurement needs a tool that supports the offset geometry.
Check vibration after the work
Belt, train and cardan drives show misalignment as vibration at once and twice shaft speed, and in the axial direction. A before-and-after spectrum is a good proof of the job.
Questions
How do I align a belt drive?
Align the sheave faces so the grooves lie in one plane and the shafts are parallel. Use a straight edge or a laser, with the belts off. Set tension afterwards.
How do you align a machine train with three machines?
Choose a fixed reference, align the next machine to it, then the following one, and re-check the first coupling because the middle machine moves both.
How should a cardan shaft be aligned?
With the end shafts parallel and equal, opposite joint angles within the maker range, so the needle bearings keep rolling.
What if the machine cannot be moved?
Use the other machine as the movable one, or shim both. If neither can move, rework the base. Do not accept misalignment outside the maker limit.
General good practice for horizontal machines driven through a coupling. The machine maker's manual, the coupling data and your site standard come first. Lock out and isolate the machine before any alignment work.