<!DOCTYPE html
  PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<!--
Copyright (c) 2006 UGS Corp.

All Rights Reserved.

This software and related documentation are proprietary to UGS Corp.
-->
<html>
   <head>
      <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
      <title>Pitch/Lead/Tpi (threads per inch)</title>
      <script language="javaScript">
        abridged="false";
        displayConditions=new Array();
      </script>
      <link type="text/css" href="../css/main_styles.css" rel="stylesheet">
   </head>
   <body class="bodydocs" onload="top.pageLoader()" bgcolor="#FFFFFF">
      <div class="title_topic3" id="xps10_pagetitle">Pitch/Lead/Tpi (threads per inch)</div>
      <hr noshade="true">
      <p class="para_topic">Pitch is the distance between corresponding points measured from one thread to the next parallel to the axis. Lead is the distance a screw thread advances axially 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 axis.</p>
      <div class="figure">
         <p align="center"><img align="bottom" src="graphics/lathe/lthread_PiAt01.gif"></p>
      </div>
      <div class="title_figure">Pitch, Lead, and Threads Per Inch</div>
      <p class="para_topic">The Pitch, Lead, and Threads Per Inch can each be specified as Constant or Variable.</p>
      <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>
      <table border="0">
         <tr>
            <td valign="top" align="left"><img align="left" src="../graphics/note.gif" alt="Note" title="Note"></td>
            <td valign="bottom" align="left" width="100%">
               <div class="para_note">
                  <p class="para_note_body"> NOTE: For Metric parts, the Threads Per Inch option is not available.</p>
                  <p class="para_note_body"></p>
               </div>
            </td>
         </tr>
      </table>
      <p class="para_division">Pitch, Lead, and Threads Per Inch are related as follows:</p>
      <p align="center"><img align="bottom" src="graphics/lathe/lthread_PiAt06.gif"></p>
      <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 above specified Pitch, Lead, or Threads Per Inch.</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>
      <table border="0">
         <tr>
            <td valign="top" align="left"><img align="left" src="../graphics/note.gif" alt="Note" title="Note"></td>
            <td valign="bottom" align="left" width="100%">
               <div class="para_note">
                  <p class="para_note_body"> NOTE: For Metric parts, the Threads Per Inch option is not available.</p>
               </div>
            </td>
         </tr>
      </table>
      <p class="para_division">Output Unit allows you to specify the appropriate output command to the postprocessor. Refer to the discussion of Output Unit above.</p>
      <p class="para_division">You may define the rate of change by specifying Start &amp; End Values or Start &amp; 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 Lathe Thread dialog box 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 Lathe Thread 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) minor word 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 system outputs a DECR (decrease) minor word and value as a field in the THREAD/ command; for example:</p><pre class="indent">THREAD/TURN,TPI,10.0000,DECR,1.0000</pre><p class="para_division">Generally, DECR causes a decrease in pitch per inch (or millimeter) over the length of the thread. Refer to your postprocessor manual for details of the effect of DECR for your machine tool/controller combination.</p>
      <p class="para_division">Increasing pitch or lead corresponds to decreasing threads per inch and vice versa.</p>
   </body>
</html>