Threads, which are the ridges or grooves along the insides or outsides of cylindrical objects, are a key part of many components in various industries. These threads provide secure joining capabilities for multiple pieces together as well as the ability to hold down an item in place or to seal a joint that transports fluid. Metric threads, Whitworth, and American National – with their specific UNC, UNF, and 8UN characteristics – are the most popular varieties of threads used in industry.
In most parts of the world, the go-to threading system is the metric thread. With its standardized designations from the International Organization for Standardization (ISO), this type of thread has become a global phenomenon apart from United States, Canada, and Mexico. This type of thread is indicated by an ‘M’ followed by the major diameter in millimeter along with its pitch represented by millimeters. For instance, an M10 x 1.5 thread has a major diameter of 10 mm and a pitch of 1.5 mm.
In the mid-1800s, Joseph Whitworth, a British engineer, created the Whitworth thread. This thread pattern is still used today in interchangeable parts that follow the same system devised by Whitworth himself. The British Standard Whitworth (BSW) labels this type of thread and it is also referred to as British Standard Fine (BSF). Following a certain format, each Whitworth thread is designated with a letter ‘W’ and two numbers. These numbers indicate the major diameter in inches and the number of threads per inch respectively. To illustrate, W10 x 1.5 has a major diameter of 10 inches and 1.5 threads for every inch.
In the first years of the 20th century, the American National thread system was created and persists in its utilization today. According to the American National Standard Institute (ANSI), this type of thread is predominantly used for applications in which requisites such as compatibility with other American National threads are not mandatory. American National threads are identified by the abbreviation UN plus the major diameter of the thread size in inches and its class. Taking, for instance, UN10 x 1.5, this would represent a thread with a major diameter of 10 inches and class 1.
To generate a thread of the desirable relationship, a hole of required dimensions must first be punched. The caliber of the orifice is contingent on the major diameter of the thread; for instance, an M10 x 1.5 thread necessitates a 10 mm aperture. Once this hole has satisfactorily been spurred, the thread itself may be hewn.
Threads can be cut in two major ways – manually with a tap and die set or automatically with a lathe. For manual thread cutting, the type of taper (e.g. plug, taper, or bottom) and the diameter constitute the basis of classification for both taps and dies that are tasked with producing internal and external threads respectively. Conversely, the same criteria are applied to determine the variety of size suitable for each tool when using a lathe for thread-cutting.
The intricate process of external thread cutting demands the deployment of a lathe machine, best used for its accurate and precise speed and feed. This, however, is preceded by the necessary grinding of the tool bit to appropriate angles and shapes. This specialised technique is called turning, during which the workpiece’s outer diameter (OD) is scenically scored without falter.
When it comes to yarn-cutting, there are three familiar methods available: manual threading with a tap and die set, turning via a lathe, or drilling with an appropriate tool. All of these methods have their own benefits as well as drawbacks.
Hand thread-cutting can be accomplished most easily using taps and dies. It is advantageous to utilize this method because any thread size can be accurately cut. On the downside, taps and dies take an extended period of time and require a great deal of dexterity.
Threads on the outside diameter of a part can be effectively cut through the use of lathes, which have been a popular choice for their speed and ease of use. Though cutting threads that are small in diameter can pose a challenge for lathes, they remain a dependable option for many applications.
A drill is the go-to instrument for crafting threads inside a workpiece; it is fast and setup is reasonably uncomplicated. Unfortunately, it’s a challenge to cut out threads with wider diameters.