At VibrAlign, we are in the precision maintenance business.  Our tools, our training, and our people, are all about precision maintenance.  While teaching the field alignment portion of our shaft alignment training, at a customer site, we went out to align a particularly troublesome pump.  They didn’t think they were getting the life they should out of the bearings and seals on this machine.

So, imagine my dismay when I see two mechanics, right out of our alignment class, who were beating a coupling onto the pump shaft.  WITH A THREE POUND HAMMER!

There’s your problem-right there!  Coupling have fits, and so did I!

Coupling manufacturers do have recommended fits.  A coupling with a keyway should have a slight slip fit-generally 0.0005”-0.0015”.  That means the shaft must be clean, and not beat up, and the coupling bore is clean, and not beat up.  If these two simple things take place – the coupling should slide on quite easily.  If it does not, find out why.

  • Measure the shaft and bore, to make sure the fits are correct.
  • Lightly sand the shaft with some emery cloth. Look for burrs, especially from set screws, and on the shoulder of the key slots.
  • Lightly file the edges of the key slots on both the hub and shaft.
  • Lightly file the key.
  • Wipe it all down to clean, and spray a light coat of lubricant. If you must use anti-seize, a light coat is best.

When you start the coupling hub onto the shaft, it is very common for it to cock a little.  Gently tap it with a dead blow hammer, to get it started true.  “Gently tap” is not easily done with a forged sledgehammer.

If it doesn’t start, repeat these steps again.  You’ll be much less likely to damage your seals, thrust load your bearings, accidentally ding up the coupling and shaft.

Does it take a couple more minutes?  Yes.  Is it worth it?  Absolutely.

For additional coupling related blogs go to: Couplings


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