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Go/No-Go Gauge?

Discussion in 'Sampling, Standards and Inspection' started by MapleQuality, Apr 13, 2021.

  1. MapleQuality

    MapleQuality Member

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    Hi,

    I have a question about the use of go/no-go gauges.
    As per the engineering drawings, there are some dimensions that have to be checked at receiving and also final inspection (i.e. parts need to be measured to ensure that they are within tolerance).

    There are two ways of performing this measurement. The first method is to simply take the parts and the appropriate measuring tools, take the required measurements and record the values. And check to see if the actual values are within the range of the acceptable tolerance.
    The second method is to create a jig (fixture) based on the dimensions/tolerances of the engineering drawing, and put the part in the jig. If the part fits inside the jig, then this means that the dimensions are within tolerance (Go/No-Go gauge). However, in this method, we will not have actual values to record, we just know that the part is within tolerance.

    I am wondering if the second method is inaccurate or incorrect in anyway? Are there any points or tips that I need to keep in mind when using the second method (because this method is faster than first method, and is more preferable).
     
  2. Evers

    Evers Member

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    I think the answer to your question is to take a risk based approach: How critical are the tolerances and what is the deviation when using the rig. Will it also be able to detect a part that is too small? What could go wrong with using the jig measurements? (forcefully cramming the part in, damage to the jig etc.)
    A jig can absolutely be a lot more workable and less error-prone than taking multiple measurements.
     
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  3. Miner

    Miner Moderator Staff Member

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    There are definitely pros and cons to either approach. Actual measurements may provide more information such as process centering and dispersion, but may be misleading (i.e., a single diameter cannot provide information on variation in form; an average diameter cannot provide information on functionality). Go/No go gages may provide less information, but provide a truer picture of functionality (i.e., will these two parts assemble correctly?).

    I agree with Evers. Look at the relative risks vs. benefits for each approach.
     
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  4. Andy Nichols

    Andy Nichols Moderator Staff Member

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    A couple of things to consider are the criticality of the features and also the life of the part, plus the history of design changes. Committing to a jig type receiver gauge might be a good option if the product is going to be around and not change for a while.
     
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