Justification of the Application of Tightening Elements in the Shaft- Hub Joint

Standardized methods of power transmission and motion transfer use different elements, such as keys, wedge-shaped shafts, polygonal shafts, and lateral pins to join the hub of driving or driven elements with the shaft, or make use of friction connections (cylindrical tightening connection, conical connection, tightening elements). Nowadays, the key is accepted as a universal joining method most frequently used in the production of single items and in the small-series production. A machine industry survey has shown that approximately 60% of all hub-shaft joints are based on the keys. Although the analysis of the hub-shaft joints should be impartial and objective, we cannot avoid the impact of engineering tradition. The choice of the joint type in practice is typically reduced to copying old solutions, adopting someone else’s standards, using solutions without a thorough analysis or “ad hoc” solutions which are appropriate to the current technical and economic situation and to the available time. Such choice can be hard to justify because a consequence of such an impulsive approach is the fact that the designer’s creativity is reduced, his/her independence is lost, and it may even create a lack of confidence 1-3 . The joints based on keys are often inadequate in meeting increasing demands for higher durability, material savings, energy and labour savings or assembly simplification. The keyway created on both elements of the joint reduces the load-bearing cross-section of the joint and increases the production cost. Its sharp curvatures increase stress due to the cutting effect. Thus, in order to achieve sufficient joint strength, the diameter and the length of both the shaft and the hub have to be increased.