Angular TP, Radial TP

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  • Angular TP, Radial TP

    I HAVE 8 HOLES THAT ARE NOT EQUALLY SPACED. LIST SPECIFES ANGLE FOR EACH HOLE.I'M MEASURING HOLE -C- WHICH IS ONE OF THE HOLES FROM THE PATTERN THEN I ROTATE MY ALIGMENT
    TO THAT BASIC ANGLE SPECIFIED ON THE LIST.THEN I DIMENSION +/- .0015 FOR ANGULAR AND +/- .0035 FOR RADIAL POSITION.
    IS THAT A CORRECT WAY OF DOING THAT OR SHOULD I USE XACT MEASURE AND DIMENSION .003AB NON DIAMETRICAL POS. SEPARATE AND .007AB NON DIAMETRICAL POS.
    I HOPE I'M MAKING SENSE WITH THAT QUESTION. ANY HELP WOULD BE APPRECIATED https://www.pcdmisforum.com/image/gif;base64,R0lGODlhAQABAPABAP///wAAACH5BAEKAAAALAAAAAABAAEAAAICRAEAOw==​PLANE- A- IS TOP SURFACE DIA -B- IS AN OD.
    B/P CALLS FOR
    tp .003 AB
    TOL PAR TO BSC ANGULAR LOC
    TP .007 AB TOL PAR TO BSC RADIAL LOC
    Attached Files

  • #2
    wow, that's quite a strange one!
    1: Both FCF's do not have a Ø symbol in it, so technically the tolerance zone should be square.
    2. Since neither FCF has any reference to C Datum, you should not be using it as a rotational constraint. You should bestfit (rotate only) the 8x pattern to itself.
    3. This is solely my opinion, but from the notes, it sounds as if your tolerance zone is not square, nor rectangular. You get 0.007" radial distance variation from centroid and 0.003" angular distance about said radius. This would produce a trapezoidal tolerance zone. really bizarre.
    4. I would dimension 8x Polar Radius to 0.007" Level to A, Origin to B and Bestfit-rotated to 8xpattern, then the same with Polar angle to 0.003".
    5: No feature MMC bonus allowed unless your GD&T is per ANSI Y14.5m revision 1973.

    Comment


    • #3
      GREGF That's two planar zones - see picture how to do it with Xact

      RadialArc.PNG

      louisd A tolerance zone is either planar (1 direction), circular (2 directions) or spherical (3 directions), never square or rectangular. At least in ISO - can you point to the ASME definition of a rectangular tolerance zone?

      AndersI
      SW support - Hexagon Metrology Nordic AB

      Comment


      • JacobCheverie
        JacobCheverie commented
        Editing a comment
        louisd I think I get what you are picturing, but take a look at Fig. 7-29 "Means this" in Y14.5-2009 carefully. If it was a truly trapezoidal zone, then the opposing planes in the angular direction wouldn't be entirely parallel. The zone edges cut off an arc, but they don't stay perpendicular to the arc as the zone expands.

      • louisd
        louisd commented
        Editing a comment
        I'll agree with rectangular tolerance zone only because it's defined TOL PAR TO BASIC ANGULAR/RADIAL LOCATION, as in the theoretical perfect point in which the feature should be, now has a rectangular tolerance zone 0.003 x 0.007 from there.

        If it didn't state the word LOCATION in the notes, I would still contest that it's trapezoidal. if tol range was higher, i'd even contest that it's a pair of arc segments as the radial tolerance zone. 0.003" is noise for any delta you'd get from the arc segments.

      • JacobCheverie
        JacobCheverie commented
        Editing a comment
        louisd But in a trapezoidal zone you are allowing for more angular error if you are on the far side of the radial error. Let’s say you have .001 radial error. You shouldn’t be allowed more angular error if the radial error is +.001 vs -.001.

        But I do agree that ultimately it is a pair of arc segments that can be approximated with a rectangle in comparison to the CMM delta.

    • #4
      1: Simultaneous requirement has to be accounted for.
      2: You have 8 rectangular tolerance zones that are .007 wide in the radial direction and .003 wide in the angular direction, one zone centered on each hole perpendicular to datum A and at a basic angle/distance from B.
      3: Find the distance to each hole from datum B center - 2X this value is your radial position (must be less than .007)

      The Position in the angular direction is a little more complicated and can be thought of in terms of a little linear algebra or linear transformations. Consider the hole in quadrant one. Let the basic distance from origin be broken into it's component form (x0, y0) such that x0^2 + y0^2 = r^2 where r is your basic radius and x0 = r*cos(A), y0 = r*sin(A) where A is the angle as measured from the X axis.
      Measure the hole and determine it's X and Y location (x`, y`) in your base coordinate system.
      Applying a linear transformation (rotation of A degrees about Z) puts you in a coordinate system where your point (x`, y`) will have coordinates (x``, y``) in the rotated coordinate system such that x`` = x`*cos(A) + y`*sin(A) and y`` = y`*cos(A) - x`*sin(A). In this rotated system, determine the distance along the Y axis from your measured point to your nominal point. In other words, find y`` - y0. Double this value and make sure that it is less than the .003.
      Last edited by JacobCheverie; 01-16-2020, 10:00 AM.

      Comment


      • A_Shomshor
        A_Shomshor commented
        Editing a comment
        ^^^^this ^^^^

    • #5
      Thank Guys I will try it I think we will ask our customer for clarification on that.When I get a chance I'll post what I find out

      Comment


      • #6
        Without a diameter symbol in the FCF, the tolerance zone is no longer round. what shape is the tolerance zone if it is not square?
        From ASME-y14-5m-2009:

        "3.6 DEFINITION OF THE TOLERANCE ZONE
        Where the specified tolerance value represents the diameter of a cylindrical or spherical zone, the diameter or spherical diameter symbol shall precede the tolerance value. Where the tolerance zone is other than a diameter, the diameter symbol shall be omitted, and the specified tolerance value represents the distance between two parallel straight lines or planes, or the distance between two uniform boundaries, as the specific case may be. In some cases the tolerance zone is nonuniform and is specified as described in para. 8.3.2."

        Comment


        • #7
          I've trying to use Xact measure for planar tolerance zones with no diameter symbol in my control frame and specifying planar axis as shown above.
          My problem with it is it's still doubling my deviation in the true position.V2016

          Comment


          • JacobCheverie
            JacobCheverie commented
            Editing a comment
            That is to be expected. If you are .001" off the center of your planar tolerance zone, your Position value should be .002". It is the size of the smallest zone that will capture the object being positioned (axis, center plane, etc...).

        • #8
          I disagree. If it was a diametral tolerance zone that's fine, but not with a planar zone.

          Comment


          • JacobCheverie
            JacobCheverie commented
            Editing a comment
            Y14.5.1 - 1994

            5.2.1 (c) The actual value of position deviation is the smallest value of t_0 to which the feature conforms. (t_0 is the size [width/diameter] of the tolerance zone).
            5.2.2 (c) The position deviation of a feature is the diameter of the smallest tolerance zone (smallest value of b) which contains the center point or all points on the axis or center plane (within the extent of the feature) of the applicable actual envelope of the feature.

            5.2.1 is for surface interpretation, 5.2.2 is for resolved geometry (axis) interpretation.

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