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      <title>Base feature strategy</title>
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      <div class="title_topic3" id="xps10_pagetitle">Base feature strategy</div>
      <hr noshade="true"><a name="ndxgenid_roadmap293"></a><a name="ndxgenid_roadmap294"></a><a name="ndxgenid_roadmap295"></a><p class="para_topic"><img align="bottom" src="graphics/commandref/ideas_rule.gif" border="0"></p>
      <p class="para_topic">In I-deas, the recommended modeling approach for most companies is to use a reference coordinate system as the first feature in the history tree. This is often called a BORN coordinate system. Using this coordinate system helps maintain associativity to features within the part model and to instances in assemblies.</p>
      <p align="center"><img align="bottom" src="graphics/parts/ideas_born.gif"></p>
      <p class="para_topic">The I-deas <b class="uiTerm">New Part</b> icon enforces this process.
      </p>
      <p class="para_topic">If you start a model by sketching on the workplane, this base coordinate system is also automatically created when you create the first extruded feature.</p>
      <p class="para_topic"><img align="bottom" src="graphics/commandref/nx_rule.gif" border="0"></p>
      <p class="para_topic">In NX, associativity is maintained by creating a base feature and then adding features that are associative to it. Three recommended procedures are shown to create a model with associative features.</p><a name="ndxgenid_roadmap296"></a><div class="title_division">Method 1. Datum CSYS</div>
      <p class="para_division">Using a <b class="uiTerm">Datum CSYS</b> is similar to using I-deas BORN coordinate system. It provides three planes, three axes, and a point at the origin that can be used for sketching and constraining. Other datum planes can be created offset from this first <b class="uiTerm">Datum CSYS</b>.
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      <p align="center"><img align="bottom" src="graphics/parts/datum_csys_anim.gif"></p>
      <p class="para_division">Create the <b class="uiTerm">Datum CSYS</b> at the origin using the <b class="uiTerm">Absolute CSYS</b> origin method, then create other datums or <b class="uiTerm">Datum CSYS</b> features offset from it.
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            <p class="para_item"><img align="bottom" src="graphics/icons/icon-datumcsys.gif" border="0"> <b class="uiTerm">Datum CSYS</b> (<b class="uiTerm">Feature Operation</b> toolbar)
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                  <p class="para_tip_body">The Model template already contains this <b class="uiTerm">Datum CSYS</b> feature.
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      <p class="para_division">The history in the <b class="uiTerm"><a class="links" href="javascript:void(0)" onclick="top.openFile('roadmap/05qt_parts_4.html');return(false);">Part Navigator</a></b> will look like this after creating a <a class="links" href="javascript:void(0)" onclick="top.openFile('roadmap/05qt_parts_21.html');return(false);">Datum CSYS</a>, <a class="links" href="javascript:void(0)" onclick="top.openFile('roadmap/05qt_parts_16.html');return(false);">sketching</a> on one of its planes, and <a class="links" href="javascript:void(0)" onclick="top.openFile('roadmap/05qt_parts_26.html');return(false);">extruding</a> the sketch:
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      <p align="center"><img align="bottom" src="graphics/parts/datum_csys_hist.gif"></p>
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            <p class="para_item">Datum CSYS feature</p>
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            <p class="para_item">Sketch</p>
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            <p class="para_item">Extrude feature</p>
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      <div class="title_division">Method 2. Fixed datums</div>
      <p class="para_division">Another acceptable practice in NX is to only create the datums that are actually referenced.</p>
      <p align="center"><img align="bottom" src="graphics/parts/datum_planes1.gif"></p>
      <p class="para_division">If you just begin a sketch on one of the WCS planes, NX will create a fixed datum plane at that location, so you are actually using this second method.</p>
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                  <p class="para_tip_body">A best practice is to avoid using more fixed datum planes than necessary, since they are not associative to each other. Instead, create relative datum planes offset from the fixed datum planes.</p>
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      </table><a name="qt_parts_primitive"></a><a name="ndxgenid_roadmap297"></a><div class="title_division">Method 3. Primitive features</div>
      <p class="para_division">In NX, starting a model with a primitive is considered acceptable practice as long as only one primitive feature is used in the model, and later features are positioned relative to it.</p>
      <p align="center"><img align="bottom" src="graphics/parts/primitives.gif"></p>
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            <p class="para_item"><img align="bottom" src="graphics/icons/icon-block.gif" border="0"> <b class="uiTerm">Block</b> (<b class="uiTerm">Insert</b>&rarr;<b class="uiTerm">Design Feature</b>)
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            <p class="para_item"><img align="bottom" src="graphics/icons/icon-originedgelengths.gif" border="0"> <b class="uiTerm">Origin, Edge Lengths</b> 
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                  <p class="para_tip_body">Primitive form features should only be used to start a part, since their positioning isn't associative. To create a second block, either sketch on a face or use a <a class="links" href="javascript:void(0)" onclick="top.openFile('roadmap/05qt_parts_22.html');return(false);">form feature</a> such as <b class="uiTerm">Pad</b> instead. 
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