April 28, 2016
Bolt Holes – Size matters!
By Steve Gordon
I was asked to help a customer align a 500HP Motor / Blower. The new motor came in on a skid, was lifted into place with a crane, new electrical boxes fitted and coupling put into place. Now the easy part, the precision shaft alignment!
We took two sets of measurements which repeated. Made one small shim correction (The motor was roughed in using the old shims which were in good shape). Using the Verti-Zontal technique we then went after the horizontal correction. While moving the motor with the horizontal jack bolts we ran out of room! We were bolt bound. How can that be? The old motor wasn’t.
What has changed? The motor. Upon further inspection the new motor has bolt holes 1” diameter. The old motor has bolt holes 1.25” diameter.
The motor had to be uncoupled, electrical removed, lifted, bolt holes enlarged and then reassembled. One day’s work, what an aggravation! I’ve been involved in machinery alignment for almost two decades and I didn’t have that one filed in my head as one of the pre-alignment checks. I do now…
As it turns out, the precision shaft alignment is again the quick and easy part. 30 minutes.