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      <title>Boundary Approximation</title>
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      <div class="title_topic3" id="xps10_pagetitle">Boundary Approximation</div>
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      <p class="para_topic">The cut parameter, Boundary Approximation, is common to both Planar Milling, &nbsp;and Cavity Milling. </p>
      <p class="para_topic">Boundary Approximation (Follow Periphery, Follow Part, Profile) can reduce processing time and shortens tool paths when the boundary or islands contain conics or B-splines. This is because that type geometry often requires unnecessary processing of internal passes (i.e., passes that are away from island boundaries or the main boundary) to satisfy tolerance constraints.</p>
      <p class="para_topic">Boundary Approximation uses part of the specified Stepover for the second and third passes of the tool path (pass one is the pass closest to the boundary, pass two is the next one in, etc.) as an &quot;approximation tolerance&quot; to allow longer linear tool motion.</p>
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                  <p class="para_note_body"> NOTE: The actual stepover and approximation tolerance for pass two are: 75% and 25%, respectively, of the specified stepover. The actual stepover and approximation tolerance for pass three are both 50% of the specified stepover.</p>
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      <div class="title_figure">Boundary Approximation</div>
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                  <p class="para_note_body"> NOTE: Boundary Approximation will not shorten a tool path if the boundary and all islands contain only lines and arcs.</p>
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