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FCF True Position, Adding MMC on Datum

Hello,

I am trying to create a true position command using FCF. I have a MMC on Datum B. Datum A is the surface perpendicular to the hole and Datum B is the OD of a part with various holes on a Bolt Circle. I set up the true position and add maximum material condition to both the hole size and Datum B. I put the size of Datum B to be the maximum size in field for "size" after the maximum material condition cell. I run the report and my bonus tolerance is almost .016, which is only taken from my hole size.

How do I get the report to include the possible additional .004 to my bonus from Datum B? We cut the hole size to almost maximum so we are getting almost all of the .016 bonus from the hole size and we cut the diameter (Datum B) to nominal, so I should be getting an additional .002 bonus from the Datum. However, in the report, it is only including my bonus tolerance from the hole size.

20X .593 ± .008
True Position | Ø.000 (M) | A | B (M)

Datum A: Plane where holes are located.
Datum B: Ø42.482 ± .002
  • Hello,

    I am trying to create a true position command using FCF. I have a MMC on Datum B. Datum A is the surface perpendicular to the hole and Datum B is the OD of a part with various holes on a Bolt Circle. I set up the true position and add maximum material condition to both the hole size and Datum B. I put the size of Datum B to be the maximum size in field for "size" after the maximum material condition cell. I run the report and my bonus tolerance is almost .016, which is only taken from my hole size.

    How do I get the report to include the possible additional .004 to my bonus?

    20X .593 ± .008
    True Position | Ø.000 (M) | A | B (M)

    Datum A: Plane where holes are located.
    Datum B: Ø42.482 ± .002


    Maximum material condition (MMC) cannot be applied to datum. You can apply maximum material boundary (MMB), which is not going to give you extra tolerance for position, but will make datum shift possible which will be visible at the end of the dimension callout.
  • The MMBoundary attached to datum B will not show up in the tolerance, as the MMC bonus of the feature size does.

    The MMB on B is datum shift, like if you made a hard box fixture and wiggled the part in it prior to inspection to get the feature to come in print.

    The report should show a row of info about datum shift, this is the "bonus" from B.
  • If you feel that you need the MMB on the DATUM, you should use XACT Meas. If you DO NOT USE the MMB bonus allowed, you will not accept bad parts. It is possible to REJECT good parts by not taking advantage of the MMB.