Parallelism / sign at datum

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  • Parallelism / sign at datum

    Hey guys
    i have a parrallelism on a surface to datum A
    and at the datum it has the symbol " / 100"
    If i remember it correctly it has something to do with the tolerance zone, that its only per 100mm?
    Can anyone explain this? And how should i do it in PC DMIS? Does normal parrallelism work?
    Last edited by pcdmisstudent; 11-26-2019, 09:25 AM.

  • #2
    Post a picture of the callout. A specific callout per area / zone is legal on Flatness. I have never seen it on // before.

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    • #3
      from ASME y14.5m 2009 spec
      5.4.2.2 Applied on Unit Basis. Flatness may be
      applied on a unit basis as a means of limiting an abrupt
      surface variation within a relatively small area of the
      feature. The unit variation is used either in combination
      with a specified total variation, or alone. Caution
      should be exercised when using unit control alone for
      the reasons given in para. 5.4.1.3. Since flatness involves
      surface area, the size of the unit area (e.g., a square area
      25 25 or a circular area 25 in diameter) is specified to
      the right of the flatness tolerance, separated by a slash.
      Here's 5.4.1.3 for reference.
      5.4.1.3 Applied on a Unit Basis. Straightness may be
      applied on a unit basis as a means of limiting an abrupt
      surface variation within a relatively short length of the
      feature. See Fig. 5-4. When using unit control on a feature
      of size, a maximum limit is typically specified to
      limit the relatively large theoretical variations that may
      result if left unrestricted. If the unit variation appears
      as a “bow” in the toleranced feature, and the “bow” is
      allowed to continue at the same rate for several units, the
      overall tolerance variation may result in an unsatisfactory
      part. Figure 5-5 illustrates the possible condition where
      straightness per unit length given in Fig. 5-4 is used alone
      (i.e., if straightness for the total length is not specified).

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