Categories: Shaft Alignment

How To Align a “Moving” Motor.

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By on June 26, 2014

After 34 years, aligning a few thousand machines, teaching millwright training for a technical college, and being an instructor for VibrAlign, I sometimes think that no alignment challenge can beat me!  Then something comes along to really put me in my place!

I was put in such a place while training at a large manufacturer in South Carolina.  This company has dozens of small utility pumps.  I will not name the pump manufacturer, and no photos will be used, but I will explain the set-up.  This machine was used for the “hands-on” portion of the training, since the company had been experiencing excessive vibration from the unit.

The pump assembly skid consists of two rails, which bolt to the floor.  This skid should normally be grouted, but this one was not.  Underneath the motor is a plate steel riser, approximately 1/8″ thick, and about 4 inches tall.  On top of this riser sat a 40 HP, rolled steel plate motor.  Rolled plate motors are not uncommon, but this was the largest horsepower motor I had seen using this type of motor construction.

The normal pre-alignments steps were completed, with a special emphasis on minimizing soft foot, since motors of this type do not have the typical four cast iron feet.  The motor housing is broken in a sheet metal brake to provide two long “feet”-one on each side of the motor.

The first alignment measurements were completed, and the motor was shimmed and moved to the values calculated using the Verti-Zontal method.  The 2nd set of result measurements were close, but not on target.  While performing live moves with the laser alignment tool, the mechanic leaned on the motor.  We noticed  movement at the coupling of over 10 mils (0.010″)!  So we stopped what we were doing, and checked every hold down bolt on the motor, riser, and base.  Everything was tight.  So, we checked again, and we still got over 10 mils of movement.

While we did not conduct any detailed study, due to time constraints, we could only assume the movement was due to insufficient stiffness of the frame, riser, and motor.  A recommendation was made to this facility to grout the base, and add some horizontal stiffening to the frame and riser.

So, how do you align a moving motor?  You do not.  You make modifications to the structure to make it rigid enough to be aligned.  If you do not, you are asking for problems.

About the Author

Stan Riddle joined VibrAlign in 2008. He has over 35 years experience in aligning industrial machinery. Stan received his AAS Degree in Machinist Technology from Surry Community College in Dobson, NC, and also holds a diploma in Industrial Systems Technology from Forsyth Technical Community College in Winston-Salem, NC, where he was also an instructor in the program.

Stan began his maintenance career working as a machinist and millwright for companies such as Weyerhaeuser, R.J. Reynolds, and Tyco Electronics. He also has over 25 years experience in Predictive Technologies, such as vibration analysis, thermography, oil analysis, and ultrasonic inspection. He is a certified Level III Vibration Analyst with the Vibration Institute, and is a Past Chairman and Board Member of the Piedmont Chapter.

Stan and his wife live in Yadkinville, NC.

2 responses to “How To Align a “Moving” Motor.”

  1. Guruprasad says:

    Dear sir
    We are having thermic fluid pump with motor coupled by spider( No:110).
    Last week we are chaiged the motor for servicing, now installed the pump but the motor droving more current as compared to previous. ( raised from 10 to 14).
    Please suggest me for perfect alignment.

    Thanks and Regards
    Primacy Industries

  2. Stan Riddle says:

    Good alignment specifications are based more on running speed. At 3600 rpm, the optimal alignment would be .05mm offset, and an angularity of about 1mm/100mm, or .01/mm. But I would suggest that if you have changed the motor, a different motor may have more to do with your current increase than alignment. Different windings, bearings, stiffness, internal bearing alignment – all of these can influence current draw.