Shaft alignment procedure
This is the order of work for a normal horizontal machine pair: prepare, rough align, remove soft foot, measure, move vertically, move horizontally, check, and document.
Pre-alignment checklist
| Check | Why |
|---|---|
| Lock out, isolate and tag the drive and the process. | Safety first |
| Read the maker alignment target and any thermal growth data. | You may need to offset the cold position |
| Clean the feet, shims and base; remove paint and rust. | Soft foot and non-repeatability |
| Confirm the pipework and conduit are free, or note them as strained. | Strain pushes the machine out after you leave |
| Check the bolt holes and jacking bolts; have shims in several thicknesses. | Avoid running out of move |
| Check coupling condition, hub fit, runout and bearing play. | See earlier chapters |
| Measure the foot distances and the coupling distance for the tool. | Wrong distances give wrong moves |
Which machine moves?
Choose a stationary machine and a movable one. Normally the heavier, piped one is stationary and the motor is the movable machine. If the machines are both piped, or both are hard to move, plan a move on both and use a tool that allows it. Before any move, record how much room you have in the bolt holes in each direction: it avoids discovering bolt-bound halfway through.
Steps
- Rough align with a straightedge and feeler gauge across the coupling, and a tape check on the shaft gap. Aim for the coupling faces to be parallel and the rims level to a few thousandths of an inch.
- Soft foot check at all feet (see the soft foot chapter). Correct before measuring.
- Mount the sensors or indicators. Tight, clean and clear of the shaft keyways. Check bracket sag if you use dial indicators.
- Take a first set of readings by rotating the shafts together and, for a laser tool, in at least three positions that cover a spread of angle.
- Read the result as vertical and horizontal offset and angle at the coupling and at the feet. Compare with the tolerance.
- Vertical move first. Raise or lower the movable machine with shims at the front and back feet. Use the tool foot values, measure the shims, and keep the stack small.
- Horizontal move second. Use jacking bolts or a push-pull device. Move in small steps and remeasure. Do not hit the machine.
- Tighten in the cross pattern, in three passes and measure again. Hold-down tightening often changes the reading by a few mils.
- Final check: repeat the soft foot check and take two sets of readings. If the result is within tolerance and repeats, stop.
- Back off jacking bolts, record and photograph the final values, and make a note of the shim stack.
Two ways to read the result
You get the answer as foot corrections (what to do at the front and back feet) and as coupling values (what the coupling sees). The coupling values tell you whether you are in tolerance. The foot values tell you what to do next. Work from the foot values, judge by the coupling values.
When the machine runs out of move
Bolt-bound means a foot bolt hits the side of its hole. Base-bound means the foot hits the edge of the base or a stop. Both appear when a machine was set at the end of its range. Options, in order:
- Check whether the other machine can move, or whether the stationary one can be the movable one.
- Move a different pair of feet. Three-machine trains can use the middle machine as the movable.
- Use a purpose-turned bolt or enlarge the hole with the engineer approval (see the shims and bolts chapter).
- Re-grout, re-drill or remake the base. This is the long-term fix.
Verify, do not assume
- If the final result holds across two sets, with the machine unloaded, you are done.
- If tightening changes the result by more than about a third of the tolerance, return to soft foot and hardware.
- After the run, check bearing temperature and vibration at the first start. A change after alignment is information.
Questions
What is the correct order for aligning shafts?
Prepare and clean, rough align, correct soft foot, measure, move vertically with shims, move horizontally, tighten and re-measure, then do a final check and record the results.
Should I do vertical or horizontal moves first?
Vertical first. Shimming changes the height, and the horizontal move is then made on a stable base.
What is bolt-bound and base-bound?
Bolt-bound means a hold-down bolt touches its hole before the machine reaches the target. Base-bound means the foot reaches the edge of the base or a stop. Both mean you have run out of move in that direction.
How do I know when to stop adjusting?
Stop when the coupling values are within tolerance and two sets of readings repeat after final tightening. Chasing zero often loses more than it gains.
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.