Projected line versus cylinder

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  • Projected line versus cylinder

    V3.7 MR2 - XP SP2
    We inspect a planer suface on a part, construct plane.
    We construct offset plane 3-1/2" from the inspected plane.
    We inspect a hole through surface, use zero depth, thick = -.125
    We inspect same hole zero depth, thick = -.5
    We create a cylinder from the two circles.
    We create a line from the two circles.
    We construct an intersection point between the line and the projected plane
    We construct an intersection point between the cylinder and the projected plane.
    I measure the distance between the two constructed points.
    Theoretical is zero, measured = .012
    How can this be.
    Both projected points use the same measured features,
    Why is the projection of the cylinder and line different in measured value?
    when they are defined by the same two circles.

  • #2
    Cylinder is calculated differently that two separate circles resulting in a different axis
    Links to my utilities for PCDMIS

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    • #3
      I understand the cylinder is different from the circles.
      I don't understand why the cylinder (centerline) is different from a line constructed from the same two circles used to construct the cylinder.

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      • #4
        If you understand that the cylinder can be different, also understand that the axis can be different. When the diameters calculate differently, you can almost bet that the axis will be different. It is related to the way the points bestfit the feature(cylinder vs circle)
        Links to my utilities for PCDMIS

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        • #5
          OK - I can understand the cylinder and line are calculated differently though they came from the same two circles.
          But the next question would be which is the more proper to use.
          It is safe to say, The correct fix here would be to take additional hits on the circles and add circles at addition levels until the measured distance between the two projected points is zero?

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          • #6
            It will depend on what the hole is for. I would say, that if this hole/cylinder is for a bolt and the projected distance is for where the bolt (stud/bar/pipe) would be at that distance from the surface of the part you are checking that you need to use CYLINDER and MAX_INSCRIBED construction method. This will give you an answer for the biggest stud that can fit through the hole and where it would intersect the offset plane (ie tightest fit, no slop on the stud).
            sigpic
            Originally posted by AndersI
            I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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            • #7
              They dont come from the same circles, they come from the same points of those circles. I dont know that the points would ever converge with certain kinds of error in the cylinder.
              Links to my utilities for PCDMIS

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