Everyone has had shaft alignments that seemed to be possessed. Whether you’re using a laser alignment system or dial indicators, one set of readings tells you to go in one direction, the next set of readings tells you something completely different. If you’re having repeatability problems, something is loose. Is it that simple? Yes!
So what can be loose? When troubleshooting looseness look for unintentional movement–movement you are not controlling. Let’s break it down to three different areas: sensor movement, base/foot movement, and torsional movement. Ask yourself these questions as you are stepping through the options.
- Are the chain brackets tight to the shaft or hub?
- Are the extension rods tight to the brackets?
- Are the sensors tight to the rods?
- If using magnetic brackets, do the magnets have full contact to prevent them from slipping?
- If mounted to a hub instead of the shaft, is the hub tight to the shaft?
- Is the sensor rubbing on something when positioning the shaft?
- For sleeve bearings, has the shaft come to rest so you know for sure it’s in the same spot for measuring?
- Did you bump something out of place?
- Are all the hold down bolts on all pieces of equipment tight?
- For all the above, are you sure?
- Are the motor feet moving relative to the base?
- Is the base moving relative to the feet?
- Is there debris in/under/around the shims and base?
- Can multiple shims be consolidated into fewer shims?
- Does this sound like soft foot?
- Is there looseness in the coupling?
- Are you controlling it in a consistent manner?
- Are you controlling the backlash in the gearing?
- Are the chain/magnetic brackets tight to the hub/shaft (see above)?