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Fun with GD&T! Datum Shift Revisited.

RobertoFlores
Ok, so it sounds like a simple question, do I get MMC/LMC bonus off a datum feature?
For example [Dia .005-M][A-M]
normal logic would state that I get bonus from my feature, and I get more bonus off my datum, that's how I have been taught to calculate it (with a calculator).
but in my little world I have the pleasure of programming in PC-Dmis and Calypso, and these programs don't always agree with each other (that's an understatement).
I've been up and down the internet, and this video is the best explanation I can find of why you don't get bonus from a datum.
I do believe the conundrum I am chasing is known as "Datum Shift / Datum Mobility".
You can search it on the internet, but reading that kind of text is difficult for me to digest, and what makes it even more difficult is that everyone refers to documents I do not have available.

But I still am left with the question of, Why does PCD give me bonus, and Calypso does not?

BTW I'm using PCD 2010 mr3, so I'm a little out of date. is this addressed in later versions?

https://www.tec-ease.com/gdt-tips-view.php?q=276
http://www.pcdmisforum.com/showthread.php?19372-Datum-Shift
http://www.pcdmisforum.com/showthread.php?21780-Pc-Dmis-Bonus-Tolerance-freak!!!-(MMC-Bonus-vs-Datum-Shift-discussion)

I would prefer simple answers like "Yes you get bonus, go ahead and add it all up" or "Stop taking that bonus, Only use the bonus from your feature".
Slight smile
Second question, what if the only modifier I have is on a datum?
Parents
  • Is there a list of XactMeasure er... measurements that do not work with constructed features?
    iirc, Symmetry is one. Adding MMB to the list. What are the others?
    I didn't even know about the Symmetry.


    There are some situations where the only option (afaik) is to construct datums from points.
    Features measured using multiple wrist angles, for example.
    I know, that's why I put in the official request to get it changed.


    aiui, probe comp is not applied correctly on measured features with various wrist angles.
    I've done it many times with no problem. Probe comp is done on each hit. How did you get it to break?
Reply
  • Is there a list of XactMeasure er... measurements that do not work with constructed features?
    iirc, Symmetry is one. Adding MMB to the list. What are the others?
    I didn't even know about the Symmetry.


    There are some situations where the only option (afaik) is to construct datums from points.
    Features measured using multiple wrist angles, for example.
    I know, that's why I put in the official request to get it changed.


    aiui, probe comp is not applied correctly on measured features with various wrist angles.
    I've done it many times with no problem. Probe comp is done on each hit. How did you get it to break?
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