Tap wrench

Two "Bar" tap wrenches and a "T" style tap wrench

A tap and "T" wrench

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A tap wrench is a hand tool used to operate any small tool that has a square drive as part of its body. These are usually cutting tools, the most common being taps, but also including hand reamers and screw extractors.

Types

The image shows three tap wrenches. All have two handles with the cutting tool connection in the center. This helps balance the torquing forces and reduces lateral forces which could snap the hardened cutting tool.

The two left tap wrenches in the image are Bar style which are distinguished by the cutting tool securing method. One of the handles is threaded so tightening the handle exerts pressure on the head of the cutting tool. In the case of the lower bar tap wrench, this moves a jaw to apply clamping pressure.

The third wrench pictured is a '"T"' tap wrench. This model uses a collet design which uses a threaded nosecap to close several collet fingers, which exert clamping pressure on the cutting tool's drive head. This style is useful where restricted clearances or extra reach is required. T tap wrenches vary in length (reach) of the main body and the diameter of the body to accommodate various sizes of cutting tool. The hole which forms the collet fingers may be stepped (have multiple diameters, usually two) to increase the range of cutting tools which may be held by one wrench size.

Use

Numerous sizes of bar tap wrenches are required to cover the available size range of tool heads. Generally speaking, the smallest size which accommodates the tool head is recommended because it reduces the risk of breakage from excessive force.

Unlike drill bits, hand taps do not automatically remove the chips they create. 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"^{[citation needed]}), possibly breaking it. 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 60 degrees until the chips are broken by the back edges of the cutters. It may be necessary to periodically remove the tap from the hole to clear the chips, especially when a blind hole is threaded.

For continuous tapping operations (i.e., power tapping) specialized spiral point or "gun" taps are used to eject the chips and prevent crowding.

References

This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate. (March 2009)

• Krar, Steve; Arthur Gill, Peter Smid and Paul Wanner (2003). "Tap Wrenches". Machine Tool Technology Basics. New York City: Industrial Press. 12–3. ISBN 0-8311-3134-9. OCLC 54363563. http://books.google.com/books?id=ZVXjUc-BCbYC&pg=PT130. 
• Moltrecht, Karl Hans (1981). "Tapping". Machine shop practice. New York City: Industrial Press. p. 367. ISBN 0-8311-1126-7. OCLC 5829600. http://books.google.com/books?id=7eaCQoBKFnkC&pg=PA376. 

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