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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
  • I do see that the standard does specify an S prefixing the diameter symbol in the FCF for true position of spherical features. It does not call it "spherical true position" per se but it does specify it.
  • We have a part here with a spherical cut and in order to locate it you have to have more than 2 axis. I'm not sure I am folowing your question in regards to datums.

    What I meant is this, even if there is no S in front of the Ø if the FCF has ABC a 3 datum callout it could become a spherical TP meaning you gonna use xy and z in your calculations.

    And what the he ll is spherical cut?
  • You can have 3 axis defining the location of your tolerance zone without your tolerance zone being spherical. It makes for a goofy drawing but I have seen it. A shperical cut is just that a cut that is the shape of a sphere, an inside sphere.
  • You can have 3 axis defining the location of your tolerance zone without your tolerance zone being spherical. It makes for a goofy drawing but I have seen it. A shperical cut is just that a cut that is the shape of a sphere, an inside sphere.

    yea,result is the same in 3d right.
  • In the help files
    Working with the "Deviation Perpendicular to Centerline" Functionality
    By default, the FCF True Position dialog box has the Deviation Perpendicular to Centerline functionality enabled in the background, as this is consistent with the ASME Y14.5 standard.

    While a Deviation Perpendicular to Centerline check box was not added to the FCF True Position dialog box (as it is the legacy dimension's True Position dialog box), you can still turn off this option by having your FCF True Position specify a spherical zone (rather than a cylindrical or planar zone). In this case the deviation is calculated from the X, Y, Z axes.

    Note: The only time you can select a spherical zone is when applying FCF True Position to a Point or a Sphere.
  • Please show me a print with 3d TP or spherical TP. To my knowledge ( I could be wrong) I have never in my 25 years in this trade seen a callout specifically identifying such an animal.

    Your interpretation may be a spherical tp. In referencing the ANSI 14.5 standard of GD & T, I can find no such animal...I am not trying to prove anyone wrong here, just I have never seen an example. Maybe I will learn something new, maybe you will....

    Page 42, paragraph 3.3.7:

    3.3.7 Diameter and Radius Symbols. The
    symbols used to indicate diameter, spherical diame-
    ter, radius, spherical radius, and controlled radius are
    shown in Fig. 3-8. These symbols precede the value
    of a dimension or tolerance given as a diameter or
    radius, as applicable. The symbol and the value are
    not separated by a space.

    Snapshot from fig. 3.8:


    From ASME Y14.5M-1994 (reaffirmed 2004)
  • I have seen 3d true position (spherical) on a few sheet metal drawings for GM.

    Just wanted to say that even IF a feature HAS three Basic Dims to it but is called out as a diametric TP (Two Axis) then I report it as two axis and use the third axis as incomplete or BASIC NO FCF. Usually it is obvious which Datum Axis is insignificant. Sometimes not. But, call me cantankerous if you want, I give them what they ask for and don't care much for second guessing Engineers.
  • i have seen 3d true position (spherical) on a few sheet metal drawings for gm.

    Just wanted to say that even if a feature has three basic dims to it but is called out as a diametric tp (two axis) then i report it as two axis and use the third axis as incomplete or basic no fcf. Usually it is obvious which datum axis is insignificant. Sometimes not. But, call me cantankerous if you want, i give them what they ask for and don't care much for second guessing engineers.

    +1!
  • I have seen 3d true position (spherical) on a few sheet metal drawings for GM.

    Just wanted to say that even IF a feature HAS three Basic Dims to it but is called out as a diametric TP (Two Axis) then I report it as two axis and use the third axis as incomplete or BASIC NO FCF. Usually it is obvious which Datum Axis is insignificant. Sometimes not. But, call me cantankerous if you want, I give them what they ask for and don't care much for second guessing Engineers.

    Whether there is a diameter symbol or whether there is a spherical symbol does not determine what axis are applicable (2 or 3) but rather the shape of the target zone. You can have a 3 axis basic dimension scenario for a feature with a diameteric (or cylindrical) tolerance zone. Like I said earlier it makes an odd drawing but I have dealt with it. I believe that is what Matt was getting at in regards to dimensioning a point that is the intersection of a diameter and a face. 3 axis define it but it is still a diameteric tolerance zone not a spherical one as the feature itself is a diameter.
  • A Japan engineer tell me , he want 3 axis call up for TP , when the S (Spherical)is add , in the Control Frame , I don't know if real or not but is very difficult to hold , in stamping manufacturing, and is more hard when the part look all twisted ...
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