MMC and LMC bonus within PC-Dmis

When reporting a true position, should the Feature MMC bonus and Datum LMC bonus be added together, to give a an overall bonus.

Pc-Dmis defaults to adding the bonuses. Is this correct ?

The drawing call out = TP | (DIAMETRIC) 0.004 (MMC) | DATUM E (LMC)

bfire85 over 6 years ago

No. A modifier on the datum allows the measured feature to shift about the datum until it hits the datum's least material boundary. Then the true position is measured against that. The added bonus comes from the feature's size based on the diameteric tolerance stated on the print.

Are your features IDs or ODs? Are you using Legacy or Xact. Be aware that legacy TP is no longer accurate to the standard when modifiers are concerned on the datums.
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JamesMuz5689 over 6 years ago

Thanks for the feedback.

Features are internal diameters. My current reporting is set to legacy.

If reported using the Xact tool, will that satisfy the drawing requirement ?
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VinniUSMC over 6 years ago in reply to JamesMuz5689

Xact is better able to properly apply MMC/LMC from the feature, and use MMB/LMB from the datum features (as datum shift).

Legacy is incapable of properly applying MMB/LMB (unless something has changed recently.)
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NinjaBadger over 6 years ago

bfire and vinni are correct.

Legacy won't deal correctly with MMB/LMB.
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joshmxz over 6 years ago

We don't the bonus on the datums unless its needed to save the part. Everyone in manufacturing here also knows that. We also do work for "said customer" that requires us to send in our programs and have them approved and they DO NOT allow it at all (even though its on their prints).

There is another thing to keep in mind when using bonus on the datums and that is the simultaneous rule. All Positions and Profile with the DRF must be evaluated simultaneous unless noted as a separate requirement. Meaning you cant shift it one way to make one feature good and shift it another to make a different feature good unless the first one is still good. PC-DMIS has a simultaneous evaluation for XactMeasure but it gets fragile.
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Kp61dude! over 6 years ago

Ewww Xact!
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JamesMuz5689 over 6 years ago in reply to bfire85

Thanks perfectly explained. Cheers
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