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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
  • Hmm... Are you absolutely sure that this is to be treated as a 3-dimensional true position?
    I'm getting a feeling that it might not be the case at all.

    A picture/sketch of the drawing and the callout would be great.

    Also, the legacy TP should be able to calculate 3D TP by checking all three axis (X, Y, Z).
  • Basically, what is called out really appears to be a target point in the center of a cylinder, which is perp. to the datum-A- surface. There is a ring that is cut in the same cylinder, basically at the same [basic] height as the target point. I think they want this so called target point of the cylinder to be within an area, so the mating part will fit. Very strange indeed I know. Usually I don't see things of this nature on a drawing. I called and left a message to speak to someone at our customers facility, to go over what their really looking for. I suspect it is in error on their part, as the sketch was produced fairly quickly, with no sign offs of approval by someone else that had examined the sketch to insure it was correct. To me, I would think the drawing should have the basic tolerancing in 2 axis, with the 3rd axis toleranced as ±. But I am not a rocket scientist on GD&T.
    I really just wanted to find out if it was possible to actual measure TP in 3 axis. As, I see it can be done in RFS using the legacy dimensions. Thanks again for all the help and comments. I appreciate it.
  • I dont see how you can possilby call out a cylinder center point as a 3D TP.

    You could do the whole cylinder and that is sort of like 3D because the whole thing is evaluated. But a single point on the axis of a cylinder is not possible in the true sense. You might with the intersection of a plane, but why on earth would you do that, it has nothing to do with the location of the cylinder.

    Someone is pulling your leg.
  • even if it is a center of the cylinder unless there is a sign S in front of the dia it's not to be treated as a sperical TP. there for it's olny evaluated in 2D
  • I dont see how you can possilby call out a cylinder center point as a 3D TP.

    You could do the whole cylinder and that is sort of like 3D because the whole thing is evaluated. But a single point on the axis of a cylinder is not possible in the true sense. You might with the intersection of a plane, but why on earth would you do that, it has nothing to do with the location of the cylinder.

    Someone is pulling your leg.

    I agree.

    You simply do not use the dimension that runs parallell with the cylinders centerline when doing the TP. Only speculations of what you are facing, but it would sure be much easier if a print/scan of the drawing was posted.
  • I dont see how you can possilby call out a cylinder center point as a 3D TP.

    You could do the whole cylinder and that is sort of like 3D because the whole thing is evaluated. But a single point on the axis of a cylinder is not possible in the true sense. You might with the intersection of a plane, but why on earth would you do that, it has nothing to do with the location of the cylinder.

    Someone is pulling your leg.

    even if it is a center of the cylinder unless there is a sign S in front of the dia it's not to be treated as a sperical TP. there for it's olny evaluated in 2D

    I agree.

    You simply do not use the dimension that runs parallell with the cylinders centerline when doing the TP. Only speculations of what you are facing, but it would sure be much easier if a print/scan of the drawing was posted.

    If the FCF calls out three datums and one is the surface that the hole is normal to, then the axis of the hole (cylinder) must be within the TP tolerance zone. Based on ANSI Y14.5 you CANNOT just verify a point projected into the plane.
    Forget the CMM. Put a pin into the hole. As close as you can to where the pin enters the part indicate its position to the basic dimensions that control it's 2d location. Now, indicate the it's position on the opposite side as close to that surface (or move away from the surface the a distance equal to the depth of the hole.) You must maintain the TP tolerance at both those locations.

    In other words, you have to evaluate the AXIS of the cylinder, not just the center of it at one surface. This is just another way of controlling perpendicularity.

    I think I am agreeing with CMMGUY and VPT here.....
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