Page 9 - THREADING CATALOG
P. 9

INTRODUCTION







              Pitch / Threads Per Inch (TPI)                    When
              Pitch and Thread per Inch (TPI) define the same   φ     = helix angle                                      INTRODUCTION
              threading feature, only in different terms.       P     = thread pitch
              Pitch - a main and common parameter for all types of metric   Dpitch = pitch diameter (effective diameter of thread)
              threads, usually expressed in millimeters. Pitch defines   π  ≈ 3.142
              the distance along a line parallel to the axis of the thread
              length between the sides of the thread profile placed in                    φ
              the same axial plane on one side of the axis of rotation.   P
                           Pitch for Metric Threads
                                 pitch                                          πxD



              Thread per Inch (TPI) - a main and common parameter            φ 3
              for all types of inch-based threads. TPI defines the   P            φ 2  φ 1
              count / number of threads per distance of 1 inch
              along the length of threads placed in the same           πxD3
              axial plane on one side of the axis of rotation.           πxD2
                            Theads Per Inch (TPI)                           πxD1
                              1”                                Lead Angle
                                                                Lead angle is the angle between the helix of thread
                                                                and a plane of rotation. The lead angle of the thread
                                                                depends on the pitch diameter, thread pitch, and
              Lead                                              the number of thread starts. This parameter can
              Lead is the distance that defines an axial movement   be represented as a sweep of a right triangle.
              of any point moving in relative motion per one full   The angle of the thread is calculated
              turn (360°) along a line parallel to the thread axis. In   by the formula given below:
              a single-start thread, the lead is equal to the thread            Lead


              pitch. In a multi-start thread, the lead is equal to the   φ = arctan   (    )
                                                                  L
              thread pitch multiplied by the number of starts.                π×Dpitch
                 Single-Start  Double-Start   Triple-Start      Lead= n×P
                  lead           lead            lead
                  pitch        pitch          pitch             When
                                                                φ L   = lead angle
                                                                Dpitch = pitch diameter (effective diameter of thread)
                                                                P     = thread pitch
                                                                N     = number of thread starts
                                                                π     ≈ 3.142
                                                                Where the thread is single-start, the lead
                                                                angle is equal to the helix angle.

                                                                Truncation
              lead=pitch     lead=2xpitch  lead=3xpitch
                                                                Truncation is the perpendicular distance to the
                                                                axis of the thread from the imaginary point of
              Helix Angle                                       intersection of two adjacent sides of the thread
                                                                profile to the nearest point of its top or bottom.
              The Helix Angle of the Thread Influences Thread Efficiency and
              Is Necessary for Calculating Torque in Thread Applications.   truncation
              The Helix Angle of the Thread Can Be Defined by Unraveling
              the Helix from the Thread, Representing the Section As a                     truncation
              Right Triangle and Calculating the Angle That Is Formed.

                               P
              φ= arctan   (  π×Dpitch   )









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