January 5, 2016
By Tom Shelton
In his blog post “Repeatability vs. Desired Outcome – parts 1&2”, Stan Riddle, one of my fellow technical trainers for VibrAlign, explains why alignment results may vary from the expected outcome. He explains in some detail a number of causes and how they are affecting your alignment process.
Many of these causes could be eliminated in your pre-alignment phase. Some may not show up until later in the shaft alignment process. Over time you will begin to see and correct potential problems before beginning the precision shaft alignment process.
We have compiled a list of possible culprits that might be the cause of unintended movement that are affecting the results your alignment. This list can be used pre or post alignment. The possible causes of unintended movement are different in many instances, however in many cases the causes are common. This list is intended to be used as a seed to help you find the source of pain in your alignment, it is not a complete list. There are other blog posts that cover many of these issues in greater detail.
To give credit where it is due, the origin of the notion of this list was provided by a student in a training class. If you would like to add to the list to help your fellow aligners please post your suggestions in the comment section.
I suggest to my classes that a laminated copy of this list be kept with the alignment tool.
– Vibration caused by attached or nearby equipment
– Interference in the laser beams – steam, condensation, rain, dust, etc. Anything that could reflect or refract a laser light.
– Loose brackets or other components
– Dirty lenses
– Inappropriate measuring mode for conditions
– Input incorrect machine dimensions on set up
– Laser beam being broken by coupling or structure
– Gross misalignment causing beam to run off of sensor
– Gross misalignment causing coupling influences of the rotational centerlines
– Dirt or debris between shims
– Bent shims
– Shims against threads on bolt
– Actual shim thickness different than stamped thickness (shims over .025 should mic’ d)
– Two people shimming, putting different shim thicknesses under the feet
– Wrong size shims. Always use the shims that give the most contact between the base and the machine foot.
– Excessive bearing or component wear- Do a lift check to determine bearing wear
– Coupling bore off center or skewed
– Cracked or broken machine case or frame
– SOFT FOOT
– Coupling wear
– Coupling insert wear
– Incorrect coupling gap
– Shaft or hub contacting opposite component shaft
– Coupling binding due to poor or incorrect rough alignment
– Pipe and/or conduit strain
– Motor “belly” contacting base
– Broken or crumbling base
– Dirt and debris under machine or machine feet
– Rusted base, bolts or feet
– Top thread of bolt hole in a threaded base pulled up creating a bump
– Stripped hold down bolts or studs
– Cupped washers (hardened machine base washers or Grade 8 recommended)
– Improper base installation (hollow or warped base)
– Mandatory Pre-alignment steps not completed or improperly executed
o Inadequate rough alignment
o Soft foot not corrected
o Improper or too aggressive tightening sequence
– Poor backlash management
– Lack of training
When all else fails!
Sometimes when things go wrong, we get frustrated and confused. We no longer think clearly and begin to “chase” the alignment. When this happens, I would suggest taking a step back to clear your head. When you return to the alignment, start at the beginning, Follow the pre-alignment steps. Sometimes the problem just disappears. You may not even be sure what it was that caused the problem.