True Position with MMC in Datum Modifers

[[Ja...]]

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.

[[Ri...]]

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.

[[To...]]

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.

[[Ri...]]

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)

[[Ja...]]

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.

[[To...]]

Please sign in to view this quote.

Bonus is only applied from the feature's tolerance. Not from the Datum Features

[[Ja...]]

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".

[[Ma...]]

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.

[[To...]]

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

[[Ja...]]

OK, after watching the videos, it makes more sense.

[[Ri...]]

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.