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True Position in 3 axis???

1CMM4ME
Ok, I have read the post regarding this so called argument that my boss and I got into today. He told me that you cannot measure true position in 3 axis, as I told him he was wrong. I know it depends on the way the FCF calls it out, but I tried to explain to him that it is possible to measure TP in 3 axis.
I have seen the formulas, so I know it's possible. I just wish I could get one of you gurus to reply back explaining that it is possible and why. I see the picture but he does not. I do not like to get into pissing matches with upper management, but I have learned a h**ll of alot from you guys, and I know this is possible. So if one of you fine gentleman can back me up on this, I would very much appreciate it. Thank you very much.
Now I am going to get a cold beer.Smiley
  • Why are you saying that one of the three is insignifican't? You yourself posted an example using 3 basics distances and one basic angle. Look at the pic I posted. In the one view there are two dimensions locating the feature, in the other view there is a final dimension locating it as a depth from another feature. If you say one of those is insignificant how do you machine the part with one of them omitted? Remeber basic dimensions define the theoretical perfect location of the tolerance zone. They may not be handy for giving feedback to the machinist or look pretty on a report but if you omitted one of those dims you couldn't make the part.
  • You are right about the fact that all FOUR are needed to define the pierce point of the hole AND to define the orientation of the feature in the example I posted. Actually, only TWO are needed but since it was done in the MANNER it was done then it takes 4 dims. The problem is that it also defines a 'depth' if you will and that has no feature control frame associated with it.
    It defines the surface that the feature is in and there is not FCF for that.

    Please see this example for a distilled picture of exactly what is being defined.



    In the case of a Diametric TP the 50 BASIC is NOT part of that. It needs a seperate FCF. The same thing is created with the 4 BASIC Dims in the illustration earlier. We have a surface defined with no FCF. Calling out TP of the hole does not cover all the cases. When we do that we need to add another FCF to control the surface or the BASIC Dims are not completely controlled.

    Here is the first one again.
    Attached Files
  • Hey Guys , sorry to keep ask the same question but , I need to Understand , can you please see the picture , in this example the position use spherical TP , TP/S1.0/A/B/C , so in this situation can I Use the "Z" or not
  • Hey Guys , sorry to keep ask the same question but , I need to Understand , can you please see the picture , in this example the position use spherical TP , TP/S1.0/A/B/C , so in this situation can I Use the "Z" or not

    Yep.
  • BTW you can not TP a surface a surface is not a FOS so that is actually an illegal callout.

    In ISO-land, that is a legal callout - but you must omit the Ø!
    ...and yes, I know that is the same as a profile callout.

    Same would go for perpendicularity. It you tack it on a diameter it has to have the diameter symbol.

    Again, in ISO-land... If you tack it on the diameters centerline, the Ø must be there. However, if you tack it on the leaderlines coming from the generating lines (? two lines drawn from the 'surfaces' of the hole) you can omit the 'Ø' - which makes it perpendicularity in one axis. So, the way the callout is 'attached' to the feature also depicts how the evaluation is to be done.

    Don't know if ASME says the same though.
  • Hey Guys , sorry to keep ask the same question but , I need to Understand , can you please see the picture , in this example the position use spherical TP , TP/S1.0/A/B/C , so in this situation can I Use the "Z" or not

    Spherical True Position dictates you MUST use three axis for calculation of deviation from nominal. So, YES you must use the Z. Now, while I have used this before with sheet metal there are those that know the spec better than I do and they will probably tell you this is illegal because it is a cylindrical feature.

    BTW, PCDMIS will do this directly and there is no need for extra calculations.
  • But the problem the Z is very difficult to hold, because you need to Square root the three axis, right
  • But the problem the Z is very difficult to hold, because you need to Square root the three axes

    PCDMIS will take care of it for you as long as you SELECT all three axis. Yes, it will be hard to hold (harder than diametric). Your Engineering people should have caught that during the quote phase.
  • END OF DIMENSION #204
    COMMENT/REPT,Rivet Hole (Stamping)
    DIM #202= TRUE POSITION OF CIRCLE CIR5
    AX NOMINAL +TOL -TOL BONUS MEAS DEV OUTTOL
    X 42.900 43.037 0.137
    Y -551.700 -551.588 0.112
    Z 18.300 19.272 0.972
    DF 5.000 0.200 0.200 0.257 5.057 0.057 0.000 -----#---
    TP MMC 1.000 0.257 1.975 0.719 -------->
    END OF DIMENSION #202
  • In ISO-land, that is a legal callout - but you must omit the Ø!
    ...and yes, I know that is the same as a profile callout.



    Again, in ISO-land... If you tack it on the diameters centerline, the Ø must be there. However, if you tack it on the leaderlines coming from the generating lines (? two lines drawn from the 'surfaces' of the hole) you can omit the 'Ø' - which makes it perpendicularity in one axis. So, the way the callout is 'attached' to the feature also depicts how the evaluation is to be done.

    Don't know if ASME says the same though.

    ASME assumes CL or center plane depending on feature type.
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