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What is a Jaw Coupling?

M. McGee
M. McGee

A jaw coupling is a device that connects two shafts together. This style of coupling is primarily designed as a method of reducing vibrations caused by minor misalignments in the two shafts. In addition to its vibration reduction, a jaw coupling is nearly fail-proof, as it connects together in a gear-like manner. A jaw coupling will transmit torque well, but the loose middle area of the coupling prevents it from safely transferring large bursts of energy.

All couplings are used to connect shafts together. These devices are generally found connecting a powered system, the driver, to a non-powered system, the driven. Couplings connect the end of the drive shaft to the end of the driven shaft in order to move power from one system to the other. Using a coupling allows the shafts to have slight misalignments and variation without damaging the system. In addition, they allow the piece to separate from one another for repair or replacement.

Man with a drill
Man with a drill

The construction of a jaw coupling is quite simple. The coupling consists of three parts; two metal pieces that connect to the drive and driven shafts and an elastic centerpiece called a spider. The two metal pieces look like a nut-style fastener with a couple of blocky teeth. These teeth connect the two halves of the connector together like the teeth on a gear. It is the appearance of these interlocking teeth that gives the coupling its name.

The spider is what makes a jaw coupling different from other couplings. This elastic piece sits in between the two metallic jaws. This piece looks like a disk with a number of small arms, giving it a spider-like appearance. These arms fit in between the teeth on the metallic jaw parts of the coupling, creating cushions for the teeth.

As the drive shaft turns, the interconnected teeth of the coupling cause the motion to transfer to the driven shaft. The spider protects the teeth and reduces wear and vibration. The elastic center also gives the coupling a significant freedom of movement, allowing shafts that are misaligned to work together properly.

In general, a jaw coupling can transfer significant amounts of torque without failure. Since the coupling works via a physical connection, the interlocking teeth, very little energy is lost during the transfer. On the other hand, the elastic connection makes transferring burst power difficult, as the sudden deformation of the coupling can burst the elastic spider.

The spider is the greatest weakness of the coupling. Even though it is the portion that gives it its superior vibration-dampening capabilities, it is also physically weak. Since the jaw coupling is physically connected, it will continue to work if the spider comes apart. The connection will become looser, and the coupling loses several of its strengths, possibly causing trouble in the system if not repaired.

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