A keyway is a square channel machined in a round steel bar that holds a square key to lock pulleys or sprockets to the bar. It is used in various components such as axles, crankshafts, and drive shafts. The size of the key must match the channel, and there are different styles of keys for different applications. Half-round keys are also used in some engine key applications.
A keyway is a square channel machined in the round on a steel bar. The channel, or keyway, provides a place for a square piece of metal known as a key to lock a pulley or sprocket to the round bar. The square key fits into both the keyway and a square slot machined in the pinion or gear. By fitting tightly between the round bar and the gear, the wrench creates a strong connection in the assembly. Typically, the keyway is machined into a piece of steel prior to any heat treating or hardening of the piece.
Many components use a keyway to produce a non-slip method of attaching rotating parts. Axles, crankshafts, and drive shafts all use a keyway to hold other components in place as they turn, and provide power to drive other mechanisms. In some critical components such as the propeller shafts, a special soft key stock is used which allows the key to detach if it contacts a hard surface. By using a shear pin or key, shaft damage is eliminated as the propeller can rotate freely without damaging the shaft.
In automobile engines, the crankshaft has a keyway machined into the nose end that holds the harmonic balancer in place. All engine accessories such as the alternator, air conditioning compressor and power steering pump are driven by belts fed by this balancer. Some of these accessories, such as the power steering pump, commonly use a keyway machined into the pump shaft to also hold the drive pulley in place.
Typically offered in many sizes, the size of the channel in the shaft and the key must be properly matched. Failure to match the properly sized wrench with the correct sized channel would result in a rough fit between the gear or pulley and the shaft. Any resulting skew could lead to a broken key or a damaged gear, pulley or shaft. There are also different styles of key that can be used for different applications.
While square key stock is the most commonly used key material, half round keys are used in many engine key applications. This half-round style of key is popular in applications where the entire key is placed under a single gear or pulley. With this key, the shaft is milled to receive the round part of the key. The remaining key emerges from the shaft as a flat, square key that slides into the groove of a gear or pulley.
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