Threading

Threads are most commonly produced by cutting or forming. Internal threads can be made with either a cutting tap or a forming tool, also known as a forming tap. Cutting taps are available for blind and through holes, with the blind tap typically equipped with a spiral flute to allow the chips formed during threading to be lifted out of the hole during the threading process, while the through tap is typically equipped with a straight flute, causing the chips formed during threading to break into short pieces and exit through the through hole. In the forming threading process, the thread is shaped in the pre-hole using a tool that does not cut material but rather molds the material into the desired shape. Threads produced by forming are of higher quality in terms of both dimensions and surface finish compared to the cutting threading method, and they form a structurally stronger thread without problems related to chip removal in the forming threading process. Thread milling can use solid carbide or indexable thread mills. Thread mills are typically used for large threads and threads in hard materials, but modern thread mills are also an efficient method for producing all external and internal threads. Thread milling does not require much power from the machine tool, and the size of the thread can be adjusted by the machine tool. External threads can also be made with thread dies (thread pack) made of high-speed steel, but this method is nowadays mainly used only for thread cleaning.

Taps are primarily attached to the machine tool with a synchronized tap holder, which has a small "micro-floating" (+/- 0.5mm) movement range. Using a synchronized tap chuck enables a longer tool life and better-quality threads. Synchronized tap holders can also use internal high-pressure cooling systems up to 80 bar.

Floating tap chucks with a traditional quick change have significantly more flexibility than synchronized holders and enable threading also in machines where the spindle synchronization to the feed motion is not precise.

When using a fixed tap holder, such as an ER collet chuck, a special ER collet for threading must be used, which has a square shank at the back suitable for each tap size to prevent the tool from rotating in the collet during threading.

When using forming taps, particular attention should be paid to the cutting fluid, to ensure it is sufficiently lubricating and thus suitable for form threading on the desired material.

The most common measuring tools used in thread production are the thread micrometer and thread caliper, which are used to measure the flank diameter of the thread. In large series, thread gauges are also used to verify whether the produced thread meets the upper and lower limit requirements.

Important dimensional data for thread production can be found in the Camcut thread tables, which contain all the necessary dimensions for the most common thread standards, such as ISO Metric coarse and fine thread (ISO 261 and SFS-ISO 965-1), MJ threads (ISO 5855), Inch UNC, UNF, and UNEF threads (ASME/ANSI B1.1), G, BSF, Ww, and NPT pipe threads (SFS-ISO 288-1 and ANSI/ASME B1.20.1), TR trapezoidal thread (DIN 103 and ISO 2904), Rd round thread (DIN 405-1 and DIN 20400, PG conduit thread (DIN 40430), BA thread and S thread (DIN 513)