A threaded connection is a detachable connection that uses threaded parts to firmly connect two or more parts. In the processing of precision parts, threaded connection has the advantages of simple structure, reliable connection, convenient assembly and disassembly, and low cost, so it is widely used. In addition to connection, the thread can also be used for fixing, adjusting and transmitting.
For the general knowledge of threads, first of all, let’s first understand the function, structure and formation of threads in the processing of precision parts. (1) The formation of thread: a triangle is wound on a cylinder, and the base of the triangle coincides with the circumference of the cylinder. The hypotenuse of the triangle forms a spiral on the surface of the cylinder. If you use a turning tool of a different shape to rotate along the spiral, you can cut triangular, rectangular, trapezoidal and zigzag threads.
Thread profile: The thread profile can be seen as a plan view (for example, triangle, trapezoid, rectangle, etc.), which is generated by moving along a cylindrical spiral. The plan is the thread profile, and different thread profiles have the same purpose.
According to different directions of the helix, threads can be divided into two types: clockwise right-handed threads and counterclockwise left-handed threads. You can also use your right hand to judge the direction of the line when machining precision parts. When judging, the palm is facing you and the four fingers are along the center line of the screw. Then look at the direction of the thread: if the direction of the thread is the same as the direction of the right thumb, then the thread is a right-hand thread. In contrast, left-handed threads are usually used for right-handed threads.
According to different purposes, threads can be divided into connecting threads and driving threads. The connecting thread adopts triangular thread, such as the thread on the screw and nut, and the driving thread adopts trapezoidal, serrated and rectangular thread, such as the thread on the lathe screw. In addition, the threads are divided into internal threads and external threads, which together form a thread pair.