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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 can say this. In GD&T if you define it you got to control it regardless of the standard used. Three locator Dims defines a 3D point at their intersection (that is 3 Dimensional Point). This is a FACT and there is no way around it. Diametric FCF controls two of those D's (2 Dimensions are controlled). This is also a FACT and there is no way around it. The third one is uncontrolled by the Diametric FCF. This is also a FACT and there is no way around it.

    That said, you need another FCF to control this third (defined) axis (Profile of the surface would work). This is my take on it and I haven't lost that argument yet with any Engineer or Engineering group. The only other choice you have is to let the third Axis go defined but uncontrolled.
  • in reply to craiger_ny
    You are correct that it is adequately constrained using "one" EXPLICIT basic dimension. However, as you pointed out the axial features having a cylindrical tolerance zone, there becomes an IMPLICIT (unspecified) basic dimension limiting perpendicularity deviation to not exceed the allowed positional tolerance. For the "one" basic dimension, you are omitting the perpendicular implicit requirement. Also, the axis (so far as one might have setup a DRF with X,Y,Z axes is necessarily unreferenced. In essence, the single basic dimension will not necessarily be in any axis except a polar radius.
  • in reply to layout tech
    Position of a plane is valid under ISO. It is not valid under ASME since a plane is not a feature of size, however the intent is the same as Profile of a Surface.
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