May 11, 2018
You Can’t Perform Precision Alignment on Un-precise “Stuff”!
By Stan Riddle
Alan Garbers with Johnson Controls International contacted me regarding an alignment problem, and asked for my advice. Here is a condensed version of his email.
A client rents portable chillers, and related equipment. They built a 125HP portable pump skid with a Bell & Gossett pump on a VFD. I was there to commission the machines and noticed they used size A shims under the corner of each motor foot. I mentioned that may be causing a soft-foot issue. They told me that the technician struggled to get the pump and motor aligned. I foolishly stated that I could do better and offered to perform an alignment. Once I got into it, I realized how much I had bitten off:
- The plate steel is 1” thick, which seems thin when supporting a 125HP motor and a huge pump.
- They didn’t clean the welding slag off the motor plate before mounting the motor.
- They welded jacking bolts at places that made it difficult to get size C shims in place, so I had to resort to size B on two of the three units.
They did not support the pump piping well and I showed them that just pushing up or down on the piping was causing the alignment to shift .030”.
Alan had some great observations about this machine! It does not matter how good your laser is, what your tolerance is, or even the quality of the machines you are aligning – IF you don’t have a good foundation.
- Sitting a machine foot on welding slag is a “no-no”.
- A 2” shim won’t adequately support a +8” foot.
- Jacking bolts aren’t much help, if you can’t get shims under the feet.
- It’s unrealistic to expect a 300 lb. base to hold down >2000 lb. of rotating machinery.
Alan shared his findings with his customer, who agreed with his recommendations. Kudos to Alan for great troubleshooting skills, and wanting to do the job correctly! Even on “temporary” machine installations, you want equipment to be reliable.
The base, and its fabrication are the foundation of the machine in more ways than one!