CNC software includes "canned cycles", that is, preprogrammed subroutines, that obviate the manual programming of a single-point threading cycle. On CNC machines, the process is quick and easy (relative to manual control) due to the machine's ability to constantly track the relationship of the tool position and spindle position (called "spindle synchronization"). Today engine lathes and CNC lathes are the commonly used machines for single-point threading. The coordination of various machine elements including leadscrew, slide rest, and change gears was the technological advance that allowed the invention of the screw-cutting lathe, which was the origin of single-point threading as we know it today. Usually 5 to 7 light cuts create the correct depth of the thread. The tool moves across the piece linearly, taking chips off the workpiece with each pass. With internal thread cutting, the piece is held in a chuck. In external thread cutting, the piece can either be held in a chuck or mounted between two centers. The process can be done to create external or internal threads (male or female). The tool moves linearly while the precise rotation of the workpiece determines the lead of the thread. Single-point threading, also colloquially called single-pointing (or just thread cutting when the context is implicit), is an operation that uses a single-point tool to produce a thread form on a cylinder or cone. It may be necessary to periodically remove the tap from the hole to clear the chips, especially when a blind hole is threaded.įor continuous tapping operations (i.e., power tapping) specialized spiral point or "gun" taps are used to eject the chips and prevent crowding. Therefore, in manual thread cutting, normal wrench usage is to cut the threads 1/2 to 2/3 of a turn (180 to 240 degree rotation), then reverse the tap for about 1/6 of a turn (60 degrees) until the chips are broken by the back edges of the cutters. A hand tap cannot cut its threads in a single rotation because it creates long chips which quickly jam the tap (an effect known as "crowding" ), possibly breaking it. Unlike drill bits, hand taps do not automatically remove the chips they create. Taps and dies Ī common method of threading is cutting with taps and dies. Thread cutting, as compared to thread forming and rolling, is used when full thread depth is required, when the quantity is small, when the blank is not very accurate, when threading up to a shoulder is required, when threading a tapered thread, or when the material is brittle. Tapping uses a tool the same size as the thread, forcing the chip through the thread for evacuation. Thread Milling has a better thread quality than tapping as it offers better chip evacuation. Rolled threads are stronger than cut threads, with increases of 10% to 20% in tensile strength and possibly more in fatigue resistance and wear resistance. They may also be cut with a lathe, tap or die. Threads of metal fasteners are usually created on a thread rolling machine. For example, thread lapping following thread grinding would fall only on the extreme toolroom end of the spectrum, while thread rolling is a large and diverse area of practice that is used for everything from microlathe leadscrews (somewhat pricey and very precise) to the cheapest deck screws (very affordable and with precision to spare). In general, certain thread-generating processes tend to fall along certain portions of the spectrum from toolroom-made parts to mass-produced parts, although there can be considerable overlap. The method for any one application is chosen based on constraints-time, money, degree of precision needed (or not needed), what equipment is already available, what equipment purchases could be justified based on resulting unit price of the threaded part (which depends on how many parts are planned), etc. There are various methods for generating screw threads. Overview of methods (comparison, selection, etc.) There are many methods of generating threads, including subtractive methods (many kinds of thread cutting and grinding, as detailed below) deformative or transformative methods (rolling and forming molding and casting) additive methods (such as 3D printing) or combinations thereof. More screw threads are produced each year than any other machine element. In manufacturing, threading is the process of creating a screw thread.
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