Keyed Versus Keyless Connection

Utilizing a key and keyway to fix rotating shafts to power transmission components, such as gears, sprockets, and lever arms is a traditional connection method. Sometimes, a setscrew is used to prevent axial movement during operation. This connection, while relatively simple and reliable when transmitting smooth, consistent power, proves to be inadequate when vibratory, shock, or reversing loads are present. The setscrews used to lock the shaft in a bore can damage the shaft.

Many engineers have turned to keyless connections to handle applications with inconsistent power. Keyless locking devices are the preferred choice in Europe. Keyless connections rely on a clamping force to hold a shaft in a bore. With the advances in motion control, higher levels of precision and compactness, reduced backlash, smaller shafts and more secure connections have become critical.

Some of the advantages for utilizing a keyed connection include:

  • A keyed connection will provide a positive stop until failure, whereas a keyless connection could allow slippage between the two mating parts if it is not assembled correctly or the design torque is exceeded.
  • A keyed connection provides a visual that the mating parts are locked in place. A keyless connection could only do so if the two mating parts were inscribed with a timing mark.
  • A keyed connection will allow for more tolerance between the two mating parts. The mating parts for keyless connections must be cleaned and machined to precise tolerances.
A keyless connection can transmit more torque than a keyed shaft due to more shaft surface contact.  Figures 1 and 2 compare the contact area of a shrink fit connection to a keyed connection.
Figure 1: Keyless
Figure 2: Keyed






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