4. Stress on the Feather Key Joints

Feather key joints are positive connections - the feather key sticks in a keyway that matches its form, without any preload.

As long as the machine parts are at rest, no forces are acting on the feather key, only when the rotary movement is started the rotary power is transmitted via the flanks of the feather key from one machine part to the other. The unit pressure at the flanks of the feather key acts on approximately half the height of the feather key. Opposite forces that are applied cause shear stresses at the level of the shaft circumference, which - with too high or discontinuously changing stress - may lead to the feather key shearing off.

Figure 9 Stress applied to the feather key joint

1 shearing stress, 2 applied forces, 3 rotary power

Changing rotary directions have to be avoided, because this may cause a wearing out of the keyway, so that the feather key does no more stick.

If highly stressed joints for alternating rotary directions are to be manufactured through, profile shafts must be used.

What kinds of feather key joints are distinguished?
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What kind of stress is a feather key in a joint exposed to during the transmission of power?
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