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      <title>Pitch/Lead/Tpi</title>
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      <div class="title_topic2" id="xps10_pagetitle">Pitch/Lead/Tpi</div>
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      <p class="para_topic">Pitch is the distance between corresponding points measured from one thread to the next parallel to the centerline. Lead is the distance a screw thread advances along the centerline in one turn. For single start threads, the lead is equal to the pitch. For double start threads, the lead is double the pitch, etc. Threads per inch are the number of threads per inch measured parallel to the centerline.</p>
      <p align="center"><img align="bottom" src="graphics/lathe/lthread_PiAt01.gif"></p>
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               <p class="para_td">A</p>
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            <td colspan="1" rowspan="1" width="186">
               <p class="para_td">Lead and Pitch</p>
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            <td colspan="1" rowspan="1">
               <p class="para_td">B</p>
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            <td colspan="1" rowspan="1" width="186">
               <p class="para_td">Threads Per Inch</p>
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      </table><br><p class="para_topic">The Pitch, Lead or Threads Per Inch can be specified as constant or variable.</p>
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            <td valign="top" align="left"><img align="left" src="../graphics/note.gif" alt="Note" title="Note"></td>
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               <div class="para_note">
                  <p class="para_note_body">  For metric parts, the threads per inch option becomes threads per millimeter.</p>
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      <div class="title_division">Constant Pitch, Lead, Threads Per Inch</div>
      <p class="para_division">The Constant options allow you to specify a single pitch, lead, or threads per inch value to be applied over the length of the thread. The two unspecified parameters (lead and threads per inch if pitch is specified) are figured automatically based upon this value and the specified number of starts.</p>
      <p class="para_division">Pitch, lead, and threads per inch are related as follows:</p>
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            <td colspan="1" rowspan="1" width="18%">
               <p class="para_td">Pitch </p>
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            <td colspan="1" rowspan="1" width="9%">
               <p class="para_td">=</p>
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            <td colspan="1" rowspan="1" width="251">
               <p class="para_td">Lead/Number of Starts = 1/TPI</p>
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            <td colspan="1" rowspan="1" width="18%">
               <p class="para_td">Lead </p>
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            <td colspan="1" rowspan="1" width="9%">
               <p class="para_td">=</p>
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            <td colspan="1" rowspan="1" width="251">
               <p class="para_td">Pitch x No. of Starts</p>
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      </table><br><p class="para_division">Output Unit allows you to specify the appropriate output command to the postprocessor. You can, for example, specify the lead value yet output threads per inch to the postprocessor. Output unit displays the following options.</p>
      <ul>
         <li>
            <p class="para_item">as defined</p>
         </li>
         <li>
            <p class="para_item">pitch</p>
         </li>
         <li>
            <p class="para_item">lead</p>
         </li>
         <li>
            <p class="para_item">threads per inch</p>
         </li>
      </ul>
      <p class="para_division">As defined assures that the output unit is always the same as the input unit.</p>
      <div class="title_division">Variable Pitch, Lead, Threads Per Inch</div>
      <p class="para_division">The Variable options allow you to define a pitch, lead, or threads per inch that increases or decreases. This option may be useful in manufacturing special purpose mechanical devices or machinery requiring increasing or decreasing speed over the length of the thread. The start and end values for the two unspecified parameters (lead and threads per inch if pitch is specified) are figured automatically based upon these values and the specified number of starts.</p>
      <p class="para_division">You may define the rate of change by specifying start and end values or start and increment values. If the start value is less than the end value or the increment value is positive, the status of Pitch/Lead/Tpi in the thread dialog reads INCR for increasing. If the start value is greater than the end value or the increment value is negative, the status of Pitch/Lead/Tpi in the threading dialog box reads DECR for decreasing.</p>
      <p class="para_division">When you generate a tool path with increasing pitch, the system outputs an INCR (increase) command and value as a field in the THREAD/ command; for example:</p><pre class="indent">THREAD/TURN,TPI,10.0000,INCR,1.0000</pre><p class="para_division">Generally, INCR causes an increase in pitch per inch (or millimeter) over the length of the thread. Refer to your postprocessor manual for details of the effect of INCR for your machine tool/controller combination.</p>
      <p class="para_division">When you generate a tool path with decreasing pitch, the output is analogous.</p>
      <p class="para_division">Increasing pitch or lead corresponds to decreasing threads per inch and vice versa.</p>
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