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    Situation in production

    A part measures outside tolerance

    At inspection a value lands outside the limit. Is it the part, the process or the measurement?

    What happens

    At an inspection a measured value lands outside the tolerance.

    What should apply

    Every inspected characteristic should be within the limits set by the drawing or the customer requirement.

    Why it is difficult

    • It is not obvious whether the fault lies in the part, the process or the measurement.
    • Other parts from the same order may be affected.
    • What is done must be possible to show afterwards.

    The context that is needed

    • The characteristic, nominal value and tolerances
    • Order and time of manufacture
    • The gauge and whether it was calibrated
    • Earlier results for the same characteristic
    • Who measured

    Is the part accepted, and what has to be kept with the value?

    Illustration · Example data
    LSLNominalUSLDiameter12.00 ± 0.0512.02AcceptedLength48.00 ± 0.1047.97AcceptedWidth8.00 ± 0.057.93Below LSLDepth3.20 ± 0.053.21AcceptedKEPT WITH THE VALUENote: new material batch, re-measureGauge: micrometer, calibrated

    Every value is compared with its own tolerance. A value outside is not just a rejected result: it needs a note and the gauge used, so that it can be investigated and shown afterwards.

    Step by step

    • Four characteristics are measured on the same part. Each characteristic has its nominal value and its tolerance, for example diameter 12.00 ± 0.05.
    • Diameter (12.02), length (47.97) and depth (3.21) are within tolerance and accepted.
    • The width is measured at 7.93, below the lower tolerance limit (LSL) 7.95.
    • A note on what happened and which gauge was used is saved with the value, so that the deviation can be investigated and shown afterwards.

    Same situation, different questions

    Who needs to know what

    The same event looks different depending on which decision you have to make.

    The same evidence for everyone

    • The characteristic, nominal value and tolerances
    • Order and time of manufacture
    • The gauge and whether it was calibrated
    • Earlier results for the same characteristic
    • Who measured

    • Operator

      Asks

      "Should I measure again, stop the machine or call quality?"

      Decides

      What happens to the part and the machine right now.

    • Quality

      Asks

      "How many parts are affected, and is it the measurement or the process?"

      Decides

      Quarantine, sort, remeasure or release.

    • Engineering and planning

      Asks

      "Is this a one-off or a change in the process?"

      Decides

      Whether the process needs investigating.

    What may follow

    1. 01Measure again, preferably with another gauge
    2. 02Quarantine and sort parts that may be affected
    3. 03Document the deviation and what was done
    4. 04Investigate the cause

    Knowledge

    Concepts that help

    Where Rektron can help

    What is available today

    When values are entered in Eyesight, the status against the limits is shown immediately for each inspection type. A logbook note can be linked to the value and explain the deviation.

    Similar situations

    Do you recognise the situation?

    Tell us what it looks like where you are, and we will go through what is needed to handle it.

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