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Positional measurements that I don't understand.

Vladimir
Hi Colleagues, I am currently working on one part which is a circle with three ears. It has positional measurements, which I had difficulty with. They are marked in red in the attached photos.
As far as I understand, if the reference point is the central circle, then the controlled elements should be controlled only along the PR, but I can not understand how to represent this in Pcdmis.
I hope you can give me some tips for this.
PS
I use 2014 version PCdmis, and xact.
PPS
Datum D what is this??! Dia 100? But it's dat A in my opinion...Alien


​
  • Is datum D used as a control someplace?
    In your snips, it looks like the only relevant datums being used in a control are A and C.
    --Engineers love to complicate prints with un-utilized datum callouts. The datum reference is noise until used in a FCF.
  • in reply to Neil Challinor
    I've seen this kind of gd&t callouts before & always wondered why engineers would make such a thing.
    On the left, what if you just create the point at D, report deviation coming from 5 & manually input into the T.P equation?
    On the right same idea but report deviation of x&y & do the same thing with T.P equation?
  • in reply to louisd
    Datum D seems to be controlling position (rotation translation and size) of the three "teeth" on the outside of the 3x A datum holes.
    I presume your third snip with the 2x positions to 1.5, SHOULD be Profile (based on the bold lines) and those FCF's should reference Datums C and D.
    the engineer needs to go back to school, haa haa!
  • Is datum D used as a control someplace?
    In your snips, it looks like the only relevant datums being used in a control are A and C.
    --Engineers love to complicate prints with un-utilized datum callouts. The datum reference is noise until used in a FCF.

    Figures. We've got too many design engineers who are great with calculus 55 & catia but spend one semester doing gd&t & nothing beyond that. After having too many fights with them, I began requesting assembly prints & build individual component programs based on how they are either machined and/or assembled. Often I toss their datum schemes out of the proverbial window.
  • in reply to MattR
    I had a friend go through ASU's industrial engineering program. They spent no more than ONE WEEK discussing GD&T.

    If you work for a big corporation that prides themselves on continuous improvement, suggest to the improvement folks that you want a design review board implemented (or to include someone with Metrology/GD&T experience if already present) before a design goes to production. super fundamental.
  • That's a good idea. Problem is plenty of those companies have kaizen but only on paper. Like GM in the 1980s I read about in few automotive related books. Plenty of good stuff on paper but zilch in practice on the shop floor or engineering office.
  • That part should have a simple alignment structure.

    "A" as the face in your drawing.
    "C" as the center bore.
    "D" the width of that tab/tooth.

    Level to the surface.
    Rotate center circle through the width.
    Set origin on face.
    Set remaining origins at center circle.

    I know that's not what you drew, just pointing out how simple this should be. Finding the answer with simplicity is very difficult for many people.
  • in reply to louisd
    Not, there is not a single mention of D in the entire drawing. Your idea that positions at 1.5 should be a profile seems quite acceptable, but it will be difficult for me to explain to other people who do not know how we live in the world of geometry, why I did it this way, not like in the drawing.
    Sometimes it seems to me that it is easier to give people the numbers of what is on the drawing (whatever they are) than to think what the designer meant and then also prove something.

  • I've seen this kind of gd&t callouts before & always wondered why engineers would make such a thing.
    On the left, what if you just create the point at D, report deviation coming from 5 & manually input into the T.P equation?
    On the right same idea but report deviation of x&y & do the same thing with T.P equation​

    At first I did just that, but it seemed to me that there was some kind of mistake in this and decided to ask here. Most likely, I will stop at this option, unless someone says that this is absolutely not acceptable.
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