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Thread: True Position Formula

  1. #11
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    rangerboat72's Avatar
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    Quote Originally Posted by mdobb829 View Post
    The basic formula for True Position is 2 x the square root of the deviation in one axis squared + the deviation in the other axis squared.

    True Position = 2√ Deviation in X + Deviation in Y

    It's hard to convey a good example of the formula with the font limitation of this forum. However, the X & Y axis are for a feature measured in the Z axis plane. If you measure in the X axis plane, you would substitute the X with Z. If you measure in the Y axis you would substitute the Y with Z.

    Subsequently, if there is a MMC modifier in the call out you would be allowed bonus tolerance.
    This is a good 2 dimensional true position calculator: http://www.efunda.com/DesignStandard...ion_single.gif

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  2. #12
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    tenndoc's Avatar
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    Thanks for all the good replies guys. I screwed my knee up last Thursday and just got back to work today.

    Wish I could post a pic but can't. I'll try it this way:

    the call out is: t/p dia. .015 to f d & e
    We make landing gear for large airplanes so everything is round and cyclindrical(sp).

    The part is shaped like a cyclinder, open on one end (the face on that end happens to be datum -e-), closed on the other end with a lug w/an approx. 4.5" hole running perpendicular to the cyclinder. Clear as mud?

    The C/L of the cyclinder is datum -d- with the face of the lug being designated as datum -f-. All datums are listed as RFS.

    It was my understanding that you simply added the third datum to the equation as Matt has shown. My partner in crime here on the 2nd shift was under the impression that there was a lot more to it than that.

    Thanks again. I can always count on you guys for the help.

    Screw It. Let's Ride

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  3. #13
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    Quote Originally Posted by rangerboat72 View Post
    This is a good 2 dimensional true position calculator: http://www.efunda.com/DesignStandard...ion_single.gif
    I have had a need for this many times. It makes life simplies.
    [SIGPIC][/SIGPIC]Summer Time. Gotta Love it!

  4. #14
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    This is an excel file with a tp calc also, downloaded from:
    http://www.geomeasure.com/documents.htm

    HTH
    Attached Files Attached Files

  5. #15

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    Ese leon...! Do you have the formula for True position with polar coordinates?

  6. #16
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    Job Jenson went thru this at a training class that to inspect a "hole" location at an angle from the primary axis ( I am assuming here thats what you are talking about ) you must align your "ALIGNMENT" to the "AXIS" of the hole. You will then be reporting the deviation from 0.0 / 0.0.. I had never had any luck trying to figure it out until I used this method.

  7. #17
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    Re. TP with polar coordinates and Schlag's comment about "align your "alignment" to the axis"...
    I would think that your alignment would be based on the actual position of the center of the pattern (most likely a bore) and the NOMINAL position of the bolt hole. Meaning you'd have to create that nominal hole location some way. You could construct a point where the hole is supposed to be, or maybe just rotate your alignment (whichever you prefer). THEN measure the actual hole. The deviation of the radial location of the hole (ie the hypotenuse of the right triangle) x 2 would be your diametrical position result. Did I say all that so that it makes sense, and sounds correct?

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