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GD&T: modifiers on datums

uncharted
First off I just want to say that I am new to this forum and somewhat new to PCDmis. This is completely different from what I was use to.
I want to say up front please forgive me if I do not understand what you are talking about which may lead me to ask more questions with what answer you post.

I will make this short and sweet. I have 2 questions.

First question
Can a person place a modifier on a primary datum? I am using xactmeasure. It will allow me but I was told by my supervisor that it was not allowed. Is this correct?

Second question
A print calls out for a modifier on the secondary datum but that datum is a constructed line. Xactmeasure will not allow me to add a modifier, I'm assuming since it is not a feature of size. Does that mean I need to tell them they cannot use a modifier for that particular datum or is there some way I can manipulate from a line to something else to get the modifier added?

Thanks to all who reply.
  • For the first question yes it is ligit too have a modifier on a primary datum. I believe when it is on datum is they consider it a boundry (mmb) when its a feature of size its a condition (mmc)

    For the second part of the question you should be able to also have a modifier on a secondary datum also. Is this the secondary datum for rotation? I have had issues with this in pcdmis with it not letting you put a modifer on a distance say between two planes or two lines. but I,ve been told in newer versions (2013) it allows a modifer on a width of a feature.
  • Yes. The secondary is used for rotation. We run version 2012 MR1. So, I may not be able to use a modifier for this particular datum since it rotates, correct?
  • If the line happens to be a midline between two surfaces, perhaps try the construvted width option. Not sure when that came out but it is in PC-DMIS 2013 MR1. That will allow the modifier to be used. Check the help file.
  • Modifiers can only be applied on features of size regardless if it is a datum or a feature measured. Points, lines and planes are not features of size and therefore modifiers cannot be applied on them. The rotation is not a factor in modifiers. If you have plane, circle, circle (primary, secondary, tertiary) for you datum set, you can apply the modifier on the secondary and tertiary datum even though the rotation goes to secondary and tertiary datum, but you cannot apply modifier to the primary datum because it is not a feature of size. If you have plane, line, point, no modifiers can be applied on datum because non of the features are of size.
  • To answer the questions regarding the legality of the specific callouts on your print I think we would need to see the print, or at least a sketch showing the callout and the the types of features to which it is applied on the print.

    In general, as has been stated above:

    1) Modifier on a primary datum feature of size = No problem
    2) Modifier on something that is not a feature of size= problem both in legality and in application in PCDMIS

    Pre-2013 versions required that you do a workaround in some situations to create a FOS that was valid in the software. You would simply dimension the distance, assign this value to a variable, and then construct a circle using this variable as the diameter input. This method is described in detail in several previous posts on this forum. Here is one:

    http://www.pcdmisforum.com/showthread.php?23200-Calculate-MMC-for-any-feature

    This isn't addressing datum shift specifically but should give you some ideas about how you might attempt to work around things that seem to be roadblocks in the software.

    Version 2013 and later has a new feature called "Constructed Width" that was added to address this type of situation.
  • Modifiers can only be applied on features of size regardless if it is a datum or a feature measured. Points, lines and planes are not features of size and therefore modifiers cannot be applied on them. The rotation is not a factor in modifiers. If you have plane, circle, circle (primary, secondary, tertiary) for you datum set, you can apply the modifier on the secondary and tertiary datum even though the rotation goes to secondary and tertiary datum, but you cannot apply modifier to the primary datum because it is not a feature of size. If you have plane, line, point, no modifiers can be applied on datum because non of the features are of size.

    +1
  • Modifiers can only be applied on features of size regardless if it is a datum or a feature measured. Points, lines and planes are not features of size and therefore modifiers cannot be applied on them. The rotation is not a factor in modifiers. If you have plane, circle, circle (primary, secondary, tertiary) for you datum set, you can apply the modifier on the secondary and tertiary datum even though the rotation goes to secondary and tertiary datum, but you cannot apply modifier to the primary datum because it is not a feature of size. If you have plane, line, point, no modifiers can be applied on datum because non of the features are of size.

    Just for a little clarity two parallel planes associated with a size between them can also be a feature of size you can't put a mod on this in older versions of pcdmis. but is still consider a feature of size and can have a mmc or lmc on the size between the two planes
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