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Linearity and Bias Requirements--Parts used and Gage families

Discussion in 'Gage R&R and MSA - Measurement Systems Analysis' started by Larry Ricketts, May 25, 2016.

  1. Larry Ricketts

    Larry Ricketts Member

    Jan 8, 2016
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    We continue to have an ongoing argument over how to conduct a linearity test and what is acceptable.

    1) for example measurement of an OD with a micrometer. I understand that it is preferable to get parts with a range throughout the tolerance in order to determine the linearity of the gage. Is it acceptable to use master gage blocks to substitute for actual parts.

    2) I have been told that we can use a linearity study on a micrometer as a family. I disagree that you can't just pull a micrometer out of a drawer and do a study using gage blocks to determine if the linearity is acceptable. Is not the purpose to determine if the gage is showing wear in particular area of the measurement range.
  2. Miner

    Miner Moderator Staff Member

    Jul 30, 2015
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    Greater Milwaukee USA
    1) The AIAG MSA Manual 4th edition states that you select actual parts throughout the working range of the measurement device which are then measured with a "master" measurement device to establish the "true" value of the parts.

    In my opinion, this introduces another source of measurement variation into the linearity study. I would recommend using master gage blocks to minimize this error. After all, you are using actual parts in the R&R study.

    2) I would disagree with this. While it is true that you can use gage families in an R&R study, individual gages can have bias (calibration) issues, and linearity is just bias throughout an operating range.
    Bev D and Andy Nichols like this.