Tapping & Threading

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------------------------------------------------- Tapping and Threading Tapping Taps (a hearty thank you to wikipedia) A tap cuts a thread on the inside surface of a hole, creating a female surface which functions like a nut. There are three basic types of tap commonly used in the shop: * Bottoming Tap: has a continuous cutting edge with no taper. This feature enables a bottoming tap to cut threads to the bottom of a blind hole. A bottoming tap is never used to cut threads in an unthreaded hole, as the cutting edges lack the taper required to successfully start into such a hole. * Plug Tap: Also known as an intermediate tap, it has tapered cutting edges, which assist in aligning and starting the tap into an untapped hole. Plug taps are the most commonly used type of tap in the shop and can be found out on the shop floor in various sizes at all times. * Taper Tap: very similar to a plug tap but has a more pronounced taper to the cutting edges. This feature gives the taper tap a very gradual cutting action that is less aggressive than that of the plug tap. A taper tap is most often used when the material to be tapped is difficult to work (e.g., alloy steel) or the tap is of a very small diameter and thus prone to breakage. The taps used in the shop are all hand taps, since they are, by design, intended to be manually operated. During operation, it is necessary with a hand tap to periodically reverse rotation to break the chip formed during the cutting process, thus preventing an effect called "crowding" that may cause tap breakage. Using a tap Tapping begins with drilling a hole with a diameter slightly smaller than the tap's major diameter. The correct hole diameter may be determined by consulting the chart further down on this page. If the hole is to be drilled, the proper diameter is called the tap drill size. To calculate the tap drill size by

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