Alignment Tolerances

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Comments (4)

• It is commonly known that if you follow the coupling specs the other components will have an increased life cycle unless something else fails such as no lubrication or lost lubrication.

  1) Posted 7:37 am, 22 October 2009 by Greg Terry

• You are correct: following the coupling spec's will increase component life-cycle when compared with no alignment spec's. However, it's a mistake to think coupling spec's are good enough for your other components. The precision alignment tolerences accepted by most precision alignment practitioners were originally developed by Ken Brook of Ludeca, Inc.
  
  "Ken decided to look deeper into the Equipment Manufacturers (Pump, Gearbox, Motor etc.) tolerances by actually calculating what it would take to get the full rated life out of the Bearings! (Notice we did not say Couplings as we need to align for the Bearings, and if you do not know that, your program is in serious trouble!) Ken found that we needed to align a little better than what was previously thought and calculated what is now the Excellent column on our “Tolerances For Shaft Alignment” card. By the way, the Manufacturer’s tolerances evolved into the Acceptable tolerance column." - Copyright 2003 Voelzow & Company, Inc. Wingate, North Carolina.
  
  You will find these tolerances are tighter than most coupling tolerances as they are aimed at full rated bearing and machine life (not coupling life). So, it's worth repeating, if your objective is to increase equipment life and thereby reduce or eliminate process interruptions, minimize equipment life-cycle costs, and save energy, choose your alignment specifications wisely.

  2) Posted 2:55 pm, 28 October 2009 by Jeromy Risner

• Jeromy's remarks are right on the money.
  
  A flexible coupling has only two missions in life: To transmit power from the driver to the driven machine and to survive in the process. Thus, a good quality flexible coupling is typically built to withstand much more misalignment than what is good for the machines involved, in terms of the vibration and other forces created. Therefore, the coupling manufacturer's 'looser' alignment standards are no excuse to relax your alignment standards.
  
  You may ask, "why do most coupling manufacturers build their couplings to allow so much more misalignment than what the standard industry alignment tolerances suggest?"
  
  There are two primary reasons:
  
  To guard against sudden catastrophic failure (the safety concern) and in order to permit machines to be deliberately misaligned in the 'cold' condition to target for thermal growth and other anticipated positional changes that may occur when the machines are put in service. If the couplings didn't have this 'extra' misalignment capacity, some machines could never run together, unless you coupled them via a spacer shaft.
  
  Alan Luedeking
  Mgr. TechSupport, Alignment Div.
  Ludeca, Inc.

  3) Posted 8:15 am, 29 October 2009 by Alan Luedeking

• These "commonly know facts" are normally just saling points from a coupling manufacturer. Any knowledgeable craftsman should want to align equipment as close to the "as operating" target as possible - requardless of what the coupling manufacturer lists.

  4) Posted 2:20 pm, 16 June 2010 by Tim Z

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