SMK -ALBA posted:

Hi, Friends,

How  to know balancing   with  Half key  or Full key.

What happened if done wrongly instead of half key vice versa.

Thanks & Regards,



Are you after a basic understanding of the process.  If so go to and scroll down a bit for a discussion.  There is also good discussion at

As far as what may happen "if done wrongly" you will essentially create an unbalance (and its dynamic forces) caused by the key or key seat.   

There is an ISO specification, ISO 21940-32:2012(en) Mechanical vibration — Rotor balancing — Part 32: Shaft and fitment key convention that covers the topic.  I think since about the early 1990's most rotors, couplings, etc. are balanced with an equivalent 1/2 key installed.  Thus, if you desire to run a motor solo, you must compensate for the material missing at the keyseat.  This could be as simple as using the motor side coupling hub (if design permits) or manufacturing a sleeve for test purposes that properly retains a fitted key.

Related discussions of this topic have occurred over the years.  You should probably review the thread at  




There was a time that ISO used full key and no key balancing for the rotor and piece.  Some countries (like the U.K. if I remember correctly) switched to the ISO convention.  

Now ISO uses the half key method.  Unless, you have parts balanced the old (very old) ISO way, use the half key method.  

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