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ER Balance Mysteries

Test performed 9-21-2012

One of the issues today is manufacturer's making claims they cannot back up.  Stating numbers, calling them certified, including pieces of paper to make you feel good but ultimately costing you more carbide.

One of these manufacturers is claiming thier ER collet chucks are balanced to G2.5 @ 25,000 RPM's.  We have customers coming to us looking for holders that have this balance.  When challenged the customer admits they are no where near 15K but feel they are getting a better holder... are they? In theory, yes... in actuality NO!

There is 2 parts to this test we are trying to answer:
  1. Is the specification realistic?
  2. Did the manufacturer do what they say?
For this test I purchase CAT40 ER16 & ER32 standard length holders that are laser marked "G2.5 25000 RPM"

I check the balance on our balancing machine.  Industry standard for collet chuck is to balance the holder bodies separately from the nuts.  Why you ask?  So the nut is not paired to the chuck.  Just like the tires on your car, you cannot change rims because the balance will change.

I setup the balancing machine, installed the retention knobs and checked the bodies for actual balance.  The 3rd picture is a PIONEER CAT40-ER32-0250 to use as a test or calibration holder to make sure the machine is reading consistently.


  1. Competitor's CAT40 ER32 chuck body - MFG Specification G2.5 @ 25,000 RPM
         Actual Readout: G12.7 @ 4,000 RPM
  2. Competitor's CAT40 ER16 chuck body  - MFG Specification G2.5 @ 25,000 RPM 
         Actual Readout: G5.8 @ 8,600 RPM
  3. PIONEER CAT40-ER32-0250 chuck body  - MFG Specification G6.3 @ 20,000 RPM 
         Actual Readout: G2.6 @ 19,000 RPM
Seeing the test failed miserably I looked at the inspection reports supplied with the holders.  It states that these holders were balanced with a collet and a pin.

I tried but could not reproduce the test results on the report.  The best I could achieve was G23.0 @ 2,170 RPM, a far cry from G2.5 @ 25,000 RPM.  Not knowing the actual size, length and weight of the gage pin or collet used makes this impossible.

  • Ultimately I do not see how the samples we received ever checked better than G2.5 @ 25,000 RPM as indicated on the report.  The best I could get was 10 times specification.
  • While G2.5 @ 25,000 RPM is possible it takes a very long time to balance.  You are trying to balance something at the edge of the machine's capabilities and you will end up "chasing your tail" trying to certify the balance.  Adding the cutter weight makes a huge difference but it is impossible for a manufacturer to guarantee this level of balance without balancing the assembly.  As soon as you do a tool change "POOF" balance is gone and you must re-balance.  So the competitor's makes claims of balance it is virtually impossible to reproduce, they are counting on you never trying!  
  • Verify and test everything!  Don't believe what you read!
  • PIONEER G6.3 @ 20,000 RPM balance is 3-6 times better than this competitor's actual balance.