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How to Size a Key for a Coupling

time2011/10/08

A key is a tool that mechanically connects a part such as gear to a shaft. The most common type is a flat key. However, there are different types of keys. They are parallel keys which can be square or rectangular, tapered and gib head keys, pin keys and woodruff keys. A equal coupling is a device used to connect the end of one shaft to the end of another.
To determine the size of a key for a coupling, you have to do some math. Information needed to work out the equations are the shaft diameter, torque and force.
You can also use a table to determine the size of the key based on the shaft diameter of the equal coupling.
Determine the force of the shaft of the key. This equals two times the torque divided by the diameter of the shaft.
Divide the force by the width of the key times the length of the key to determine the shear stress.
The length of the key should equal coupling two times the torque divide by the width of the key times the shaft diameter times the shear stress.