True Position Datum can't change to MMC

[[Ak...]]

Does anyone know how to change the Datum reference in True Position to MMC?
I need to measure the true position of a cylinder hole with a cylinder as a Datum A
Then how to toggle on the MMC button in datum reference
Any help would be appriciated.

Untitled.jpg

[[Mi...]]

Hello Akish,
In order to activate MMC in the True Position characteristic window, you must first tolerance the datum features that you wish to derive your MMC tolerance from.

In the attached photo you can see on the left that I put a tolerance on the datum feature that the MMC comes from and on the right you can see that I was able to select MMC from the drop down box in the True Position window.

Hopefully, my expert powerpoint skills help 🙂

Capture3.PNG

[[Mi...]]

Michael, that's very helpful, thanks. I was having a problem with that also. But I had a tertiary datum that was a 2d line and when I put it in it turned off my mmc to the secondary datum. I tried a plane also and that didn't work. I used a single point instead and it worked fine.

[[Mi...]]

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Try it with a 3d Line? I think I overheard an app engineer mention that at some point through my travels.

[[Mi...]]

I just gave it a try. I used the 2 points I created for the tertiary datum and created a 3d line. Then I used the 3d line as the tertiary datum and it turned the mmc off on the secondary datum. I switched back to the single point and it was available again.

[[Ma...]]

I think you are missing something here. Your print does not callout a tertiary datum. If you are adding it only to get MMC on the secondary datum you are not allowing datum mobility as the print calls out. You are robbing yourself of the datum mobility (shift) allowed.

Mark

[[Mi...]]

Mark, my apologies. I am not the original poster. I just had a similar problem and added to his thread. I am sorry for high jacking his thread a little.

[[Me...]]

Calypso can only apply 'Datum Shift' in 2D with cylindrical features. Here are a few things to keep in mind:

1) Modifiers will only be activated when the datum feature(s) are cylindrical elements and reside in the same plane as the considered feature.

2) The shape of the tolerance zone must be cylindrical.

3) Using a "Point" as a datum feature does not work in the position characteristic. If you're getting a result, either a bestfit has occurred or the base alignment is being used for the evaluation.

[[Ri...]]

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I use non cylindrical features all the time, am I not understanding what you posted?

Calypso True Position.jpg

[[Ma...]]

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I don't feel you hijacked the thread. We want to create discussion and present different ideas. That is the most important thing.

I agree that the feature must lie in the same plane as the considered feature in order to have MMC and datum mobility. The OP can try and switch the datum selection around and might get MMC on the feature.

Mark

[[Me...]]

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Cylindrical Elements: Circle / Cylinder

[[Ak...]]

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Well Thank you very much for your reply,
I already tried it but unfortunately I still couldn't change to MMC
Maybe the main problem because software cannot shift position of the datum if it's not within the same plane with the feature
But then the question, how is the measurement method to measure in this kind of situation?

[[Ak...]]

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I do agree with that
But then how could I measure in condition which drawing needed for position shifting in datum that have a different plane with a considered feature, Is there anything I could try?

[[An...]]

This is my point of view.
See attached.

True_Pos_Cyl_Cyl_Flat_1.pdf