Tap wrench

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

A tap wrench is a hand tool used to operate any small tool that has a square driving head as part of its body. These are usually cutting tools, of which the most common are taps. Other small hand tools, such as hand reamers, might employ a tap wrench.

[edit] Types of tap wrenches

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, 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.

[edit] Proper use and safety

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.

Taps and reamers are hardened by heat treatment during manufacture. Although this hardness promotes long tool life, it also induces brittleness, so the tool must be used with more care than other hand tools.

Unlike drills, taps don't automatically remove the chips they create. A tap cannot cut its threads in a single rotation because it creates long chips which quickly jam the tap, possibly breaking it. Therefore, in 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" (closed bottom) hole is threaded.

Reamers, on the other hand, are never reversed in use. To clear any chips, the whole tool is withdrawn and the chips carefully removed from the hole and between the reamer's flutes. Withdrawals must be often enough to prevent packing of the chips. The likelihood of breakage is reduced considerably if there is space for the chips to move out of the way. Reamers may be manufactured with either straight or spiral flutes to assist the cutting action as well as the movement of chips.

Even though the tap wrench and its tools are operated at low speed, the use of safety glasses is highly recommended. Tool breakage can cause metal shards to be released at high speed. Also, when a tap is used to thread a blind hole, compressed air may be used to clear chips from the workpiece, and this absolutely requires the use of protective equipment.