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Inserts Driving Me Bonkers...A Better Way?

The Rook
Thanks for reading.

I've been working on a project. It's actually starting to drive me a little crazy. We need to pass a Cpk on this thing before it hits production.

The main issue holding up everything is the reporting of the inserts. Rarely do they check good. Right now, I have one part out of 11 that is good across the board.

This is a molded composite part. With 10 inserts molded into it. The inserts are either hand loaded by an operator or an insert loader that was not made very well.

The flange with the inserts is facing YMINUS. All my Basic dims match up to print. The X values are sopt on for the most part. It's the Z values that are off anywhere from .005 to .030".

Again the inserts are manually loaded.


The also when hand loading have to tap inserts on extended pins.

I know it isnt the CMM. Management says its the CMM.

These inserts as well have mmc as do the datums. Any ideas on how I could maybe can measure these inserts better, if at all?

Sorry about the book and thanks for your time.
  • One way to (hopefully) get management to see that the CMM is working properly is to manually check the part.
    1. Place your datum plane on the gage blocks.
    2. Zero out your indicator on your plane surface
    3. Run indicator over the inserts and report your results. Hopefully they'll match the CMM
  • Unless you're doing something silly, it's not the CMM. If you're working for a company that just wants you to fake the data, resign. The company will also use you as a scapegoat in the event the product injures people.

    As far as Cpk/PpK calculations go, true positions with MMC bonus would have to be calculated as a percentage-of-adjusted tolerance you're consuming (for each part),, and you would also have to assign a simulated negative-100% in some of your calculations. Even then, it's not going to be statistically valid.
  • What sort of inserts are we talking about, do they extend out from the flange or just set into the flange like grommets? Maybe the flange itself has some bend to it? I.E. bottom of the flange and top of the flange have significantly different Y values?

  • If you are seeing variation pretty much exclusively in the Z axis, explain that to your boss.

    --Maybe your composite part needs to be restrained?

    --Maybe the template or jig they are using to cut the holes for the inserts has a defect on it (raised material/debris/damaged pocket or face) and needs to be repaired.

    Comprehensively problem solve, instead of telling them "it's bad mmkay". 

    I guarantee not only will they value your approach, but you maybe could use it as leverage for a raise in the future.

  • We have some pretty large composite parts here, our issue tends to be that the primary datum is too small to control the part properly so we get wild variations in one axis while the other two are pretty close. If we use a best fit things looks pretty good, to the datums pretty bad. 
    If your CMM is failing to locate the holes you could always turn on manual hole finding. 

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