[Ja...] Posted September 12, 2023 Share Posted September 12, 2023 We have a part where we are having some issues. There are 4 holes (Ø.250" +.003"/-.000") with a True Position of | Ø .003 (MMC) | A MMC| B | C (MMC) |. I cannot get the MMC to stay when I setup the Characteristic in Calypso. Once I put in the line for Datum C, the MMC callout disappears and reverts to RFS. To try and get it to work, I am thinking I need to generate a theoretical circle using the distance for Datum C as the Diameter with a tolerance of ± .010", but I dont think that is correct. Any help would be appreciated. Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/ Share on other sites More sharing options...
[Ri...] Posted September 12, 2023 Share Posted September 12, 2023 If you are using Calypso 2023 - you can do this, but you would need to use the Simultaneous Evaluation via the new GD&T Engine. In previous versions, you would need to use a Bore Pattern, and use the View Tolerance evaluation. It appears that your DRF is fully constrained, so you would not allow any Translation or Rotation. Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-30350 Share on other sites More sharing options...
[To...] Posted September 12, 2023 Share Posted September 12, 2023 Please sign in to view this quote. Are you sure? Picture a functional gage where the datum simulators for Datum A and C made at MMC. Seems like rotation and translation would be possible. Not saying the drawing is right but rather trying to get into the engineer's head. Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-30352 Share on other sites More sharing options...
[Ri...] Posted September 12, 2023 Share Posted September 12, 2023 Please sign in to view this quote. Once again - the features are not allowed to translate and rotate. They are allowed to have their Datum shift around. If you turn on Translate/Rotation, you might as well not have a DRF as it is only being constrained Spatially. *Edit* The Translate/Rotate options are intended for non-fully constrained DRFs, and Composite tolerances (the subsequent tiers) Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-30354 Share on other sites More sharing options...
[Ja...] Posted September 13, 2023 Author Share Posted September 13, 2023 I have it setup as directed, but I am still not getting the MMC Bonus from Datum A. Datum A (outside Ø) is measuring 2.7447, so we should be getting .0053 Bonus tolerance from MMC, but it is not applying it. Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-30356 Share on other sites More sharing options...
[To...] Posted September 13, 2023 Share Posted September 13, 2023 Please sign in to view this quote. Bonus is only applied from the feature's tolerance. Not from the Datum Features Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-30358 Share on other sites More sharing options...
[Ja...] Posted September 13, 2023 Author Share Posted September 13, 2023 So how do we get the bonus from the Datum tolerance to apply? I just setup a Result Element with the result answer being the maximum diameter of Datum A (2.750) minus the actual diameter of Datum A, then using a formula for the Tolerance of the true positions to be "getActual("MMC BONUS FOR LOCATION OF .250 DIA. HOLES").actual+0.00". Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-30360 Share on other sites More sharing options...
[Ma...] Posted September 13, 2023 Share Posted September 13, 2023 Please sign in to view this quote. I've tried that too on 2018 - but on frist try it allowed me MMB - next try it was grayed out. When i tried first circle, then line then plane - then it gave me MMB on circle - but i can not get MMB on line. Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-30362 Share on other sites More sharing options...
[To...] Posted September 13, 2023 Share Posted September 13, 2023 It is my understanding that if the position passes without needing the datum shift, it will not apply it. https://www.youtube.com/watch?v=2PMb03qyOQo https://www.youtube.com/watch?v=JMiNzKPVnhU https://www.youtube.com/watch?v=uO8sKPZhAkY Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-30364 Share on other sites More sharing options...
[Ja...] Posted September 13, 2023 Author Share Posted September 13, 2023 OK, after watching the videos, it makes more sense. Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-30366 Share on other sites More sharing options...
[Ri...] Posted September 13, 2023 Share Posted September 13, 2023 The terminology that Calypso used is horrible because it's not MMC - it is MMB when applied to a Datum Feature. Like Tom said, no bonus tolerance it given when MMB is applied, but the allowance for Datum Shift. So typically what you will see is that your error is reduced with MMB as the Datum has shifted/floated to help remove the deviation from the basic dimensions it controls. Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-30368 Share on other sites More sharing options...
[Pa...] Posted December 7, 2025 Share Posted December 7, 2025 In addition to what others have said, Datum Shift is intended to apply to all holes of a pattern simultaneously. If one hole would "benefit" from shift but another would be pushed OOT by that shift, shift will not be applied. If, say, your basic bolt circle is oversized (Ø3.144 too large), but the circumferential locations are all correct, datum shift cannot improve your results. Likewise if the bolt circle is perfect, datum shift can attempt a rotation as allowed by feature tolerance but there may not be a datum shift that can bring all holes into tolerance if the angular location of one hole is too far from nominal. If your bolt circle is near perfect, and the angular spacing between holes is also really good, but the entire pattern is shifted to the datums in the same direction (translation and / or rotation), datum shift will improve results. I agree with Richard's observation that shift is applied when rotation / translation allowance boxes are unchecked when MMB is applied. However I've not found an appropriate use of these checkboxes. If I need a special rotation but don't use it, the rotation checkbox will not rotate to that special and positions still report big numbers. Link to comment https://qualityforum.zeiss.com/topic/7242-true-position-with-mmc-in-datum-modifers/#findComment-143141 Share on other sites More sharing options...
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