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Tapping tools, or taps, are cutting tools that are used to cut or form a thread in a nut or a hole. The process where the threads are formed by tapping tools is called tapping whereas the process of creating threads is performed by dies is called threading. To compare the tapping tools and dies, dies are designed to cut the male part of the mating pair such as a bolt, and tapping tools can form the female part like a nut.
With threads like bolts, tapping tools are screw-like cutting tools that have the design of multiple flutes and grooves that are responsible for creating a unique profile of gears. The spiraled flutes interrupted the continuity of cutting of thread, resulting in the sharp cutting edge. Tapping is either performed by hand tapping with a series of tapping tools like a first tap, intermediate tap, and final tap, or by machine tapping that utilizes machines when tapping a high volume of holes.
Typically, tapping tools are made of high-speed steel or carbon tool steel. High-speed steel is the most common and popular material, it is cost-effective however shortest-lived.
Two main methods of tapping are hand tapping and machine tapping. Rather than using a set of tapping tools in hand tapping, machine tapping utilizes machines such as radial drilling machines, lathes, bench type, and pillar type drilling machines, vertical drilling machines, VMCs, HMCs, and so on. Machine tapping is done on these machines with a special attachment. Nuts tapping machines use long machining taps which have larger radius right-angle bends. On the other hand, the shanks of the taps have a smaller diameter, allowing tapped nuts to slide up. The nuts can keep the machining taps at the center position, after completing the tapping, the nuts will slide off and eject from the end of the shanks.
While the machining taps work against the workpieces, the incorporation of the friction clutch and bevel gear makes the taps rotated in the cutting direction. When pulling back the feed lever, another bevel gear and reverse clutch will make the machining tap work in the opposite direction. Machine tapping is preferred today since it performs rapid, high precision tapping work due to the removal of human error. It is ideal for high-volume production.
Although the development of machine tapping and tapping tools enhances the accuracy and efficiency significantly in industrial applications, inevitable problems still occur during tapping such as tap breakage. The common operation failure or tap-related causes for tap breakage include the wear of tapping tools, improper tap geometry, inferior quality machining taps, clogging with chips, misalignment between the tools and the holes, improper lubricant, and improper rotating speed. Advanced tool holders are designed to minimize tap breakage in machine tapping, such as CNC tool holders.
Tapping tools can be divided but not limited to the following 5 types. All of them have the function of cutting the inside surface of a hole and forming the female surface like nuts.
It has a continuous cutting edge and typically has 1 or 1.5 threads of taper. Bottoming taps are ideal tapping tools for efficiently cutting the bottom of blind holes. Usually, they are used to tap the holes that have already been partially threaded since bottoming taps are relatively short.
It is also known as a second tap or plug tap. Generally, it has 3 to 5 tapered threads. They are mostly responsible for supporting the alignment and starting the tap for untapped holes.
Taper tap: The tapping tools are similar to the second tape but have 8 to 10 tapered threads. The feature makes the cutting gradual and suitable for difficult materials such as alloy steel. Taper taps usually have very small diameters which more likely lead to breakage.
Unlike the above-mentioned manually operated hand taps, power taps are driven by a power source. The most common type of power tapping tool is spiral point taps, which are also known as gun taps. The spiral point taps are capable of continuously breaking the metal chips and ejecting them forward, preventing the chips from crowding and breaking the devices.
Forming taps are also known as flueless taps or roll taps, which are quite different types of tapping tools. Unlike other tapping tools that rotate into the holes to create threads, they forcefully displace the workpieces into the thread shape. Without flutes and chips that are created during tapping, forming taps require no time and adjustment to pause the operation and clear away the chips. The feature and tougher tapping of the forming tap make it suitable for cutting blind holes.
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