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      <title>Effect of ambiguity</title>
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      <div class="title_topic2" id="xps10_pagetitle">Effect of ambiguity</div>
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      <p class="para_topic">This example shows why it is important to choose a tolerance scheme that does not lead to ambiguities.</p>
      <p class="para_topic">In this case, there is a rotor with two flanges, as shown in the figure below:</p>
      <div class="figure">
         <p align="center"><img align="bottom" src="graphics/qs_rotor.gif"></p>
      </div>
      <div class="title_figure">Rotor with ambiguous tolerancing scheme</div>
      <p class="para_topic">The tolerances are:</p>
      <ol type="1" start="1">
         <li>
            <p class="para_item">A size tolerance of 10+/-0.01 controls the overall rotor.</p>
         </li>
         <li>
            <p class="para_item">Each flange is controlled by a size tolerance of 1+/-0.015.</p>
         </li>
      </ol>
      <p class="para_topic">You are interested in calculating the minimum and maximum distance between the internal flanges. In Tolerance Stackup Validation, the measurement will be between the internal faces F1 and F2.</p>
      <p class="para_topic">Although this is a common way to dimension similar cases, this tolerance scheme is ambiguous, and the calculation from Tolerance Stackup Validation can bring unexpected results.</p>
      <div class="title_division">Why this tolerance scheme is ambiguous</div>
      <p class="para_division">Assume you are on the shop floor to machine this rotor, starting from a bar.</p>
      <p class="para_division">The overall dimension of the rotor is controlled by T1. You cut a piece according to the specified dimensions. So far, there is no ambiguity.</p>
      <p class="para_division">Next, you want to machine the flanges. The only information for the operator is the size of the flange (T2 and T3), but no location of the flange is specified.</p>
      <p class="para_division">From where should you start to machine the flange, since no datum or origin is specified. Each external face has two tolerances (T1 and T2 for the left face, T1 and T3 for the right face) that are not related to each other. Which tolerance should control the external faces?</p>
      <p class="para_division">This ambiguity needs to be resolved before a Tolerance Stackup Validation calculation can be performed.</p>
      <div class="title_division">An alternate, non-ambiguous tolerancing scheme</div>
      <div class="figure">
         <p align="center"><img align="bottom" src="graphics/qs_rotor_alt.gif"></p>
      </div>
      <div class="title_figure">Rotor with non-ambiguous tolerance Sscheme</div>
      <p class="para_division">The difference in this case is that T2 and T3 are not size tolerances. Instead, they are directed dimensions where an origin (datum) is specified.</p>
      <p class="para_division">Now there is a clear sequence for machining the features:</p>
      <ol type="1" start="1">
         <li>
            <p class="para_item">The overall rotor is cut to dimension according to T1.</p>
         </li>
         <li>
            <p class="para_item">The external left face is taken as the origin. From there, the internal face is cut to dimension according to T2.</p>
         </li>
         <li>
            <p class="para_item">The external right face is taken as the origin. From there, the internal face is cut to dimension according to T3.</p>
         </li>
      </ol>
      <p class="para_division">Because the scheme does not have any ambiguity, it is now possible to correctly calculate the minimum and maximum distance between the two internal faces.</p>
      <p class="para_division">This is the summary from the Information window:</p>
      <p align="center"><img align="bottom" src="graphics/qs_rotor_info.gif"></p>
      <p class="para_division">The total calculated variation is 0.08, the sum of T1+T2+T3. The contributor calculation also indicates that all three tolerances participate to the variation of the internal flanges, but the flanges' tolerances have a higher impact because they are bigger than the overall size tolerance.</p>
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