Feb 29, 2024
1, Basic tooth profile of ordinary threads for
The geometric parameters of fastener threads depend on the basic tooth shape within the axial profile of the fastener thread. The basic tooth shape is the theoretical tooth shape shared by the inner and outer threads formed by cutting off H/8 at the top and H/4 at the bottom of the original triangle (equilateral triangle). This tooth profile has the basic dimensions of a thread.
Figure 1 Basic tooth profile of ordinary thread for fasteners
(1) Major diameter D or d
(2) Trail D1 or d1
Minor diameter refers to the hypothetical cylindrical diameter that coincides with the top or bottom of the internal or external thread. The minor diameter of the internal thread is represented by D1; The minor diameter of the external thread is represented by d1.
(3) Mid diameter D2 or d2
Mid diameter refers to the diameter of an imaginary cylinder or cone, whose generatrix passes through the groove and protrusion width on the thread profile, and this imaginary cylinder is called a mid diameter cylinder. The generatrix of a diameter cylinder is called the diameter line, and its axis is the thread axis. The basic dimensions of the combined inner and outer thread diameters are equal, that is, D2=d2.
(4) Single pitch diameter
(5) Pitch P
(6) Half angle of tooth shape
The tooth profile half angle refers to the angle between the tooth side on the thread profile and the vertical line of the thread axis. The half angle of the tooth profile of a regular thread is 30 degree .
(7) Thread turning length
1. The influence of pitch error on the interchangeability of fastener threads
Pitch error includes both individual pitch error and cumulative pitch error. The individual pitch error is independent of the screw length, while the cumulative pitch error is related to the screw length or working distance. The cumulative error of pitch refers to the maximum difference between the actual distance between any two teeth with the same name and the nominal value within a given length range. The influence of pitch error on the interchangeability of fastener threads is shown in Figure 2.
Figure 2 Influence of pitch error on the interchangeability of fastener threads
2. The influence of tooth profile half angle error
3. The impact of single pitch diameter error
4. Principles for determining the qualification of the effective pitch diameter and thread pitch diameter
