Threading is the process of creating a screw thread. More screw threads are produced each year than any other machine element. There are many threading processes including, cutting threads with a tap or die, thread milling, single-point thread cutting, thread rolling and forming, and thread grinding. A tap is used to cut a female thread on the inside surface of a pre-drilled hole, while a die cuts a male thread on a preformed cylindrical rod. A metalcutting tool used to form a thread on a part. Threading tools include thread cutters, taps, threading dies, threading heads, thread-milling cutters, and thread-cutting abrasive disks.
The various types of threading tools used are discussed here. Threading Taps and Dies, are common method of threading is cutting with taps and dies. Hand taps do not automatically remove the chips they create as in case of drill bits. A hand tap cannot cut its threads in a single rotation because it creates long chips which quickly jam the tap, possibly breaking it. Single-point threading, also known as single-pointing, is an operation that uses a single-point tool to produce a thread form on a cylinder or cone. The tool moves linearly while the precise rotation of the workpiece determines the lead of the thread.
Thread forming and rolling, are processes for forming screw threads, with the former referring to creating internal threads and the latter external threads. In both of these processes a threads are formed into a blank by pressing a shaped die against the blank. These processes are used for large production runs because typical production rates are around one piece per second. A rolled thread can often be easily recognized because the thread has a larger diameter than the blank rod from which it has been made, however, necks and undercuts can be cut or rolled onto blanks with threads that are not rolled.
Thread casting and moulding, the threads are directly formed by the geometry of the mold cavity in the mold or die. When the material freezes in the mold, it retains the shape after the mold is removed. Thread grinding, is done on a grinding machine using specially dressed grinding wheels matching the shape of the threads. The process is usually used to produce accurate threads or threads in hard materials. Thread lapping, rarely, thread grinding will be followed by thread lapping in order to achieve the highest precision and surface finish achievable. This is a toolroom practice when the highest precision is required, rarely employed except for the leadscrews or ballscrews of high-end machine tools.
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